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  • EV conversions – a code of practice

    Code Of Practice for Repowering / Converting Vehicles to Electric propulsion (EV)

    We wrote this as a guide for those thinking about designing their own EV conversion, it’s based on OEM methods and UK requirements. It’s not definitive, but worth understanding.

    Code Of Practice Version 4. 13/03/2024

    A. Process management

    1. Keep a build register which records the vehicle ID, the serial numbers of removed engines and fitted motors, the type, condition and location of battery cells/modules, type of contactors and type and location of MSD/isolator switches. This helps registration of the vehicle and may help if you have to make warrantee claims in the future.
    2. Keep a register of approved suppliers and a record of supplier approvals which should include how they maintain quality, their returns policy, guarantees/warranties and how continuity of supply is maintained. Just in case something goes wrong and you need to show you were responsible about buying the right parts.
    3. Write a document giving clear instructions on safe usage of the vehicle, charging procedure, and what to do if it breaks down. Make it clear where the safe jacking points are and where a lifting jack must not be placed. Also give clear instructions on how to recover a vehicle, whether it can be towed and if there are towing restrictions such as maximum speed or duration of the tow. This is helpful if you sell the vehicle, or keep it yourself and need reminding in years to come.
    4. On completion of the conversion make a final vehicle Sign Off document, include evidence and results of tests on the HVIL, earth bonding faults, isolation tests, isolation monitoring etc.
    5. All road-going converted EV must have all the relevant documents submitted to DVLA to allow them to update the V5 document to show fuel type as electric.
    6. All parts should be sourced from reputable suppliers with quality standards such as ISO9001 to ensure parts meet the described specification.
    7. Guidance contained in ECE R 100 (latest version) should be followed. The functional guidance in ECE R 100 Part 1 is a minimum requirement, the guidance in Part 2 should be followed.

    B. Warnings

    1. Labels should be fitted in the engine bay or a similar location which clearly shows jacking points, prohibited jacking areas, towing restrictions for vehicle recovery and location of HV isolators.
    2. HV components including inverters, HV junction boxes and battery packs must be clearly labelled as High Voltage. Where covers are fitted over such parts the cover must have a label indicating that HV parts are behind.
    3. All HV cables must be have an orange coloured outer insulation or conduit. Where covers are fitted over such cables the cover must have a label indicating that HV parts are behind.

    C. Location of HV components

    1. No battery packs may be placed in primary crumple zones, or in vulnerable areas on vehicles without identifiable crumple zones. As a guide packs should not be in front of the forward edge of the front tyres or behind the rear edge of the rear tyres.
    2. Packs mounted under the vehicle must not be the lowest part of the vehicle structure and must have protection against road debris hitting the packs, such as robust under-trays.
    3. No HV components including cables may pass through the occupied areas of the vehicle unless fully protected by a solid cover that cannot be removed without specialist tools.

    D. High Voltage safety

    1. All HV parts must have a High Voltage Interlock Loop fitted such that if any part of the HV system is physically exposed the the packs will not energise. The HVIL must pass through all HV connectors. It is recommended that cover plates on HV junction boxes or inspection points with HV behind them are also in the HVIL by use of micro switches or connectors.
    2. All packs must switch off when the ignition is switched off or when a crash is detected. If you implement smart charging, where the VH pack and DC/DC converter cut in to keep the chassis battery charged, then ensure that there are clear warnings to let any service tech, first responder or MOT tester know that the system may turn on.
    3. Crash detections, either by G sensor and calibrated ECU or by mechanical inertia switch should be fitted to all road going vehicles such that the HV system will de-energise and isolate in a crash where you would normally expect airbags to go off.
    4. All HV parts should be sealed to IP67 standard unless it can be shown to be safe with lesser protection. It must be assumed the vehicle will be driven through flood waters up to the level of the top of the tyre and all components must be resilient to water ingress from standing water at that level and also from water splash generated by driving at speed through standing water.
    5. It must not be possible to touch HV live components with hands, fingers or small tools such as screwdrivers without removing secure panels or fixings that require tools to remove.

    E. Vehicle structure

    1. When modifying a vehicle its strength should not be compromised, hopefully this is fairly obvious.
    2. Where modifications are needed to chassis or structural parts then adequate reinforcement must be made based on a thorough understanding of the magnitude and direction of applied forces. Consider extreme driving conditions and crash situations.
    3. Only those with the correct level of mechanical engineering skills and knowledge should attempt structural modifications.
    4. Where structural modifications are made the force vector calculations, static and dynamic loadings, moments of inertial etc. that have been calculated should be entered in the build book. If there is any doubt then do not modify any structural part.
    5. When fitting packs or motors the forces must be fed in to the vehicle structure in such as way that the mounting will not fatigue or break in repeated heavy usage or in a crash.
    6. Consideration must be given the the weight of the items and force generated in a crash with particular emphasis on protecting occupants of the vehicle and ensuring no heavy parts rip out of the vehicle and hit other vehicles or people.
    7. It is recommended to use existing engine and gearbox mounting points where possible and appropriate.

    F. High Voltage cables

    1. All HV cables and parts must be isolated from the low voltage system and chassis/body, this must be tested at a voltage above the maximum system voltage.
    2. All cables must be Automotive grade with a temperature range of -30 to +50C or better. They should be tolerant of solvents and fuels as well as vibration. Domestic cabling or welding cables do not have weather and temperature protection needed in a vehicle.
    3. HV cables must have an orange outer.
    4. HV cables must be supported every 400mm or as recommended by the cable manufacturer in such a way that thermal expansion and contraction will not strain the cables and that the cables cannot fret or wear against any other part of the vehicle.
    5. Cables must not rest on surfaces loosely, such as inside of closed chassis sections, such that they could rub and wear. Cables passing through panels must be supported by a cable gland or fitting such that fretting and wear is prevented.
    6. All HV cables must be protected from impact from road debris, fitting in wheel arches should be avoided unless adequate shielding is in place. Cables routed under the vehicle floor must be protected by shielding of robust material that would reasonably stop road debris damaging the cables.
    7. HV cables outside of battery boxes and conductive enclosures such as metal distribution boxes must be shielded with one end of the shielding connected to the vehicle chassis ground.

    G. Pack construction

    1. All battery boxes on a vehicle must be adequately strong so as to remain intact in the event of a vehicle collision. Pack structure must be adequately strong, such as EN220 Steel or CR6050 aluminium. Fragile materials such as wood and soft plastics should not be used. Strong plastics and composites may be used for pack panelling but only in non structural parts of the pack unless it can be shown that they provide adequate crash protection.
    2. The pack must be constructed such that it could reasonably be expected to resist external fire (spilt fuel on the road) for at least 130 seconds to allow evacuation of the vehicle.
    3. Battery pack must have a semi-sealed ventilation system, usually containing a method of restricting moisture ingress, which is rated for the size of the pack but allows safe venting in the case of cell failures.
    4. All battery packs must have contactors on all High Voltage (HV) connections such that neither the positive nor negative cables from the pack may be live when the pack is switched off.
    5. Functional Insulation monitoring must be fitted such that any breakdown in insulation of any HV component to the body or any non HV component is detected and the system is prevented from energising, or if the fault is found whilst running a safe shutdown procedure is initiated.
    6. Bonding straps or cables must be fitted on all HV units, packs, inverter etc, to ensure there can be no potential difference between any conductive surface that can be touched.
    7. Battery packs must have a Battery Management System that prevents over and under voltage on a cell level, ensuring the cells are balanced to the cell manufacturer’s specification.
    8. Battery packs must have a Battery Management Systems that prevents over temperature by reducing available power and shutting down if an upper limit, as proscribed by the cell manufacturer, is reached. Typically this will de-rate above 50C and shut down at 60C for lithium cells.
    9. The Battery Management System must be able to detect welded contactors. If detected then it must prevent start up and show a warning of EV Failure on the dash.
    10. The BMS must be able to detect excessive current and force a safe shutdown.
    11. All HV battery packs must have a suitable HRC fuse of automotive grade which is rated for the voltages and current expected.
    12. Cell tapping wires must be protected by a low current fuse (typically 0.2A) as close to the cells as possible such that the vast majority of the cell tapping wire from the BMS is protected. Cutting an modifying existing cell tapping wires should be avoided due to the risk of shorting wires, OEM module connections should be used where possible.
    13. All packs must have a means of isolating the HV, separate to the service contactors, to allow safe removal and handling of packs in the workshop or in emergency situations. It is highly recommended to use a Manual Service Disconnect which physically removes a link in the HV battery chain. Alternatively an additional contactor may be fitted to provide the same function, this will be powered via an isolator switch with a lockout mechanism (provision for padlocking etc.) or a removable link, the isolator may disable multiple packs where more than one pack is fitted in a vehicle.
    14. The location of MSDs or isolator switches must be clearly labelled on the vehicle in a location that is reasonable to expect emergency services to look, such as under the bonnet. The location information should also be logged in the build book and also in the information pack handed to the customer, it may also be issued to emergency services.

    H. Charging systems

    1. Charging ports must be mounted such that they will not bend or break even if the charging cable is tugged. There must be a way for the plug to be locked in place (e.g. solenoid for Type 2 based sockets, latching lug for Type 1) and a detection system such that no current is passing the charging pins when the plug is disconnected. A visible charging indicator must be fitted.
    2. Where DC charging is fitted the cables from the socket to the HV system must be isolated such that under normal drive mode the cables and DC pins in the charging socket are not connected to the HV system, e.g. fitting two contactors to the DC charging cables.

  • Getting better MPG

    I’ve tested a lot of cars over the years, proper scientific tests at vehicle manufacturers and I’ve noticed a few things about fuel consumption, yes it’s a fascinating topic and I regularly enthral audiences at parties with my stories….

    In many test over the years I’ve found the difference between the smoothest driving and harshest driving results in about 30% difference in fuel consumption, even in a convoy of test vehicles all starting at the same time and arriving at the same time. There is a real art to smooth efficient driving, so I’d recommend getting some expert tuition, it also reduced wear on the car and is generally safer. It involves looking ahead, reading the road and driving to a plan. It’s a good skill.

    There is a non-linear relation between speed and fuel consumption, most family cars seem to save up to 11% on motorways by going at 60mph instead of 70mph. But keeping a steady speed is just as important. The less aerodynamic your car is the more dramatic the speed effect is. The power needed to push a car through the air is proportional to the cube of the speed, so if you double the speed you need 8 times more power. That’s one of the reasons why land speed records are so difficult.

    Tyre pressures make a big difference, if you are supposed to have 30psi but you are running 20psi you will be using up to 10% more fuel and wearing them down faster. But going over the recommended pressure makes only a slight difference and can reduce grip. So check your tyres regularly. It’s amazing how many cars are running the wrong pressure, so few drives actually check.

    Tyre type also makes a big difference too, chunkier tread uses more energy. I tested a few options on 4x4s over the years and a chunky AT tyre uses about 20% more fuel than a summer road tyre on an average commute, and really chunky MT tyres can use over 40% more fuel. So look at the energy rating of your tyres next time you buy some.

    You may have heard that your should remove all the unnecessary junk from your boot, well although vehicle weight makes a difference it’s only a very small difference, and taking 50kg out of a 1500kg car is negligible. Unless you are actually on a race track.

    Combustion engines don’t run at their best when cold, modern petrol engine heat up fairly quick but diesels can take a bit longer, so plan ahead and combine several trips in one so you are not starting with a cold engine.

    If you have a manual gearbox then make sure you are in the right gear, which is not necessarily the highest gear. An engine is at it’s best efficiency at the RPM where it makes peak torque, somewhere between that and maybe 1500 RPM works best for many cars, but try a few runs an vary your method to see what works for you.

    It may come as a surprise but servicing is really important, using good oil in the engine and transmission makes a big difference, I once picked up a ‘spares or repairs’ Peugeot 306 which gave 25mpg on my commute until I changed the tar like old oil for new, it jumped to 40mpg, the most dramatic difference I have encountered. Proper servicing is actually an investment that pays for itself.

    The old argument about air-con vs having the window open is a bit complicated as it depends on the weather and how you are driving. The drag of an open window is small compared to overall drag even up to 60mph, above that it becomes more significant. Whilst air con used in the UK can use an average of 3 to 9 bhp on a typical family car, compared to an average of 25bhp used to maintain 60mph on a motorway, so it makes a significant difference. At lower speeds like city traffic where you will use less average power the air con still uses the same power, so the difference is more noticeable, maybe up to 14% more fuel used for a town commute.

    Roof boxes add drag, but again this becomes increasingly important as the speed rises above 50mph, in city traffic it makes little difference but on the motorway it will definitely consume more fuel, so if you are not using the roof box then either take it off or drive a bit slower to save fuel.

    So basically take it easy, plan ahead, service your car and check the tyres.

  • The future of the past

    Our entire way of life IS going to change. For many of us life is already very different to how it was just a couple of years ago.

    The Anti-Car movement is gaining ground, and with some good reasons such as road deaths, pollution, congestion, noise etc. Climate change is also changing the public mood rapidly and governments are realising that action is needed, and when governments take action the results are often unpredictable.

    Make no mistake; the car and private car ownership is about to get a whole lot more contentious and problematic.

    Classic cars, bikes and trucks are wonderful things, they bring great joy to many people, not just the owner. They also help support a vibrant industry with amazing specialists and incredible skills. There is a bigger picture.

    We all know that classic cars are a very small contributor to climate change, low annual mileages and simple maintenance are crucial points. But even though it’s a small part of the problem, it is still part of the problem and so a very easy target.

    We can, of course, become part of the solution. Making physical changes to our vehicles to avoid the environmental issues, moving to net zero fuels such as synthetic or even pure ethanol, not using our vehicles in congested areas, using vehicles to bring joy and supporting charity events for instance.

    But we have to act now, and we have to gently educate others to show the positives of classics.

    Yes, it means we will have to spend money and modify our classics. But the alternative, where we are seen as a public enemy and legislated out of existence, is not worth thinking about.

  • Classics

    Your Classic car is worth so much more than just money, it is a piece of our engineering heritage, a physical testimony to all the people who designed it, built it and maintained it for all those years. It’s living history.

    We have to value our engineering heritage more than we currently do, not just for perfectly valid nostalgic reasons but for the very practical point that lessons from the past are vital when solving problems of the future. So many times I’ve seen very bright young engineers designing solutions that have basic flaws due to their lack of experience and knowledge of previous ways of solving very similar problems.

    The is a huge wealth of knowledge in our classic vehicle community, methods of machining obscure parts, use of alternative materials, the skill gained from years of experience of being able to look at something and instantly knowing if it will work or not.

    For instance one of the very modern systems in engine management ECU’s uses the change in resistance of the mixture, measured at the spark plug, as it get compressed to indicate compression and hence control spark timing as appropriate, this technique is part of the ignition control on some variable compression ratio engines. This idea came about by observing how trembler ignition works on a Model T Ford.

    And that means we should all cherish our fantastic engineering heritage, and we should also do our best to enlighten those who so far have failed to appreciate it. Car shows are one of the many great places to do this, engaging with people who already appreciate the fantastic lines of a beautiful old vehicle or relish the atmosphere that our classic car community creates, they are already head down the road to enlightenment so let’s all do our bit to share the enthusiasm for great machines and the people who made them.

    If you don’t already know much about the engineering on your classic, which is fine, I’m not suggesting it is something for everyone, it can be fascinating to dig a little deeper and find out more. Look at what makes your car different to other models and ask why did they do that? The answers are often shrouded in myth but often fascinating, sometimes there was a great idea about making a performance or efficiency improvement by doing things in a different way, sometimes it’s down to the complexities of manufacture or simple cost savings. What ever the reason for unique features in your car there is always a story behind it.

    And whether that unique idea worked or failed there is always something very valuable to be learned from it. Some things change because there is a clear advantage to a new method, such as fuel injection or electronic ignition, but sometimes it’s not so clear why old methods died out, such as Trafficators.

  • Brake judder

    Brake judder can be caused by a number of things, sometimes difficult to accurately diagnose. Most often it will be because the disc does not run true in the calliper, this could be because the disc has warped due to excessive use (quite rare) or was fitted incorrectly (more common). Another cause on older car is where the disc has corroded unevenly, particularly if the car has stood for a while, sometime the area under the pads remains untouched whilst the rest of the disc rusts.

    Fitting discs is not just a case of bolting them on and hoping for the best, any slight unevenness where the hub meets the disc can tilt the disc slightly, a small error near the centre makes a big difference near the edge of the disc, anything over 0.1mm of variation is a problem. If there is any slight tilt in the disc it will gradually worsen as it wears unevenly, initially it might feel fine but typically it becomes a big problem between 2000 and 4000 miles after the discs have been changed.

    For this reason after you have removed the old disk it is vital to clean up the mating surface, initially clean off all the dirt from the area then using a flat edge ensure the mating surface is completely flat. It should only take a moment to do but makes a big difference.

    It’s remarkable how many ‘professional’ places don’t do this.

  • The theory of cheap motorsport.

    Motorsport at any level is hugely enthralling, but the costs are prohibitive for the vast majority of enthusiasts. There are, however, a few ways round this and it is possible to do a day’s competition for less than the cost of a full tank of fuel.

    The fastest cars in drag racing accelerate from 0 to 100mph in 0.8 of a second, and exceed 330mph in ¼ of a mile, but they will spend 500 quid on fuel for each run, followed by replacing most of the 50 grand engine. By comparison The Slow Car Club take bangers usually costing less than 500 quid up the track at Santa Pod on Run What Ya Brung days, entry costs 35 quid for a whole day of driving flat out. It doesn’t matter how fast the car is because after the first few runs you start trying to beat your own personal best time, it is highly addictive and lots of fun.

    If you have ever fancied rally driving but haven’t got a rally car and baulk at the £300 entry fee for even the smallest of events then drop down a few gears and look at Production Car Trials. As the name suggests the cars are standard and there are classes for different engine sizes and engine/drive configurations, 4x4s are banned. The set up is simple; take a muddy hill with a few obstacles, mark out a challenging twisty course and see how far you can drive a car up the track before getting stuck. About the only modification you can make to the car is dropping the tyre pressures. The tracks are divided into 10 sections and you get penalty points depending on how badly you do, if you manage to get all the way up then you have no penalties and its a clear run. The skill required is remarkable and it is easy to get utterly immersed in the task of coaxing your banger that extra few inches up the track, it’s just as addictive as high speed track racing and highly recommended.

    Another variant on the rally theme is the 12 Car Event, this is a navigational event run on public roads so speeds are modest. A route is issued to the drivers at the start line and timekeepers are stationed at the end of each section, the skill is in the teamwork between the navigator and driver to ensure the best route is taken and speed optimised to make sure the car arrives at precisely the right time. It’s very competitive and requires self control as much as car control, going to fast is as bad as too slow.

    You have probably seen some footage of cars being expertly drifted round a very tight course laid out with cones in a car park. This is Autotesting and is a measure of drivers skill against the clock whilst negotiating hairpin bends, reverse parking and tight slaloms. You’ll need good tyres to get the best out of the car but for road car classes that’s about the only thing you can change. Precision and pace are needed in bucket loads, you think you can handle a car – this will make you think again!

    But if driving flat out round corners is high on your needs list then consider Hill Climb or Sprints, this is usually on race tracks and does require a race licence so the costs start mounting but it does mean you can drive at high speeds on real circuits. The idea is simple – to get fro the start line to the finish line as fast as possible and its wonderful to watch as there is often old F1 machinery operating in the upper classes. If you wonder what the difference is a Hill climb is up hill and a sprint is on the flat, more or less.

    In fact there is a surprising wealth of cheap motorsport opportunities in this country, if you are handy with the spanners then there is Grass Track (sprint races in a field), Comp Safari (rallying for grown ups), economy runs (more fun than you might think) and even real circuit racing can be done on a budget of less than £10000.

    What would you like to race?

  • Know your engines

    The engine- throbbing heart of the car, and it gives the car soul too. But how many of us really know anything about it?

    The basics of how your engine work are fairly simple, but modern engines have little details that would scramble the brains of Einstein. Luckily I will gloss over them and keep it simple!

    Basic principal.

    Mix fuel with air and set fire to it, it goes bang and expands damn fast. Now that’s fine for pyro effects in films but doesn’t push a car along. The engine converts the explosion energy into a twisting motion that can eventually drive the wheels using some fairly simple mechanics.

    It works by keeping the explosions in cylinders, usually about the size of beer cans. The top of the cylinder is sealed with the cylinder head which has valves in to let air in, and some more to let exhaust gas out. The other end of the cylinder has a piston in which is pushed down by the exploding gas.

    Now if that was all there was then the explosion would just launch the piston into the ground like a badly aimed cannon ball, so the piston is connected to some mechanical links, which as it turns out are exactly like the ones on a bicycle. No, really they are. When you pedal a bike, your legs move up and down, imagine your knee is the piston and your lower leg is the

    connecting rod (con rod) which moves the pedals which are on a simple crank, and that’s how up and down is turned in to round and round. Two pedals on a bike are like two cylinders of an engine, engines with more cylinders just use a longer crank with more pedals on.

    All that lot needs to be held in place by something pretty solid, this big lump of metal is called the engine block. Some engines separate this into two bits, the cylinders in a cylinder block and the crank in a crank case. The bottom end with the crank in is sealed off underneath with a glorified bucket called a sump, which catches all the oil running out of all the well lubricated rotating parts.

    Valves.

    Each cylinder needs a valve to let air in from the intake system, and another one to let the burnt gas out into the exhaust system. The valves are usually like the stem of a wine glass, or a penny on a stick if your not posh. The cylinder head has holes cast through it to let gas pass, called ports. The valves are stuffed into the ports so that the valve head blocks the port off at the cylinder end. Pushing the stick part of the valve down lifts the valve head off the valve seat in the cylinder head so that the gas can pass. It only lifts a few mm so the shape of the valve seat makes a big difference to how much flow there is, and so power. Its these little details that the really good tuners sort out.

    Stroke.

    The valves have to be opened and closed at just the right point in the cycle, a four stroke engine opens the intake valve so that as the piston moves down it drags air and fuel mix into the cylinder, that’s the first piston stroke. Then the intake valve is shut and the piston comes back up on the second stroke, squashing the mixture. If you compare the size of the mixture at the bottom of the stroke to how small it is at the top of the stroke you usually find that its been compressed by roughly ten times, this is the compression ratio. The compressed mixture is set fire to near the top of the stroke, which forces the piston back down on its third stroke which is the one stroke that makes any power and pushes the car along, all the other strokes actually use power. Then when that’s done the exhaust valve opens and the piston comes back up, the fourth stroke, pushing the exhaust gas out. Then it all starts again, at full chat it might repeat 100 times a second.

    Cams.

    So what makes the valves go up and down then? That’d be the cam shaft, its a long stick with lumps on, its located above the valves (usually) and spun round in sync with the crank and pistons so that the lumps hit the top of the valve stems and force them open at just the right moment. The valve then returns shut again because it has a very stiff valve spring pushing it shut, unless its a ‘Desmo’ engine, but that’s another storey for another time!

    The cam is designed to open and close the valves to give the right performance, its a complex subject but the design of the came lobe shape has a massive effect on how well the engine breaths and is one of the top tuning parts.

    There are loads of variations on this theme, most modern engines double up on valves and have two for intake and two for exhaust in each cylinder, just to get more gas flow and power. Many use two cam shafts (twin cam), one for all the inlet valves and another one for the exhaust valves.

    Cams don’t directly touch the valves, the follower reduces friction and can be either a steel disk, called a shim, which sits in a little bucket, or sometimes there is a little lever, called a rocker, and sometimes its a little hydraulic cylinder, called a tappet, which is pumped up with oil so that it automatically sets just the right valve clearance, which is crucial to getting good performance and reliability. This clearance has to be great enough that when the valve is shut it sits hard against its seat, otherwise there is a chance high pressure hot exhaust will be pushed through and burn the seat out. But if the clearance is to large then the valve won’t fully open and it will make a clattering sound as the lobe hits the follower with a thump, which can be damaging.

    The cams are driven by either a chain or a toothed belt that is driven by the crank, which has to go round twice for the pistons to do the four strokes, so the cams are driven at half the speed of the crank y having a drive pulley twice as big as the one on the crank .

    The cam and crank pulleys are usually linked by a belt or chain which is aligned so that the cam opens the valves at just the right moment, this is cam timing. If the valve opens too soon or too late then less gas is pumped through the engine and power drops, and if the timing is way out the valve might hit the piston at the top of the stroke and that means big engine damage. Adjustable Vernier pulleys are available to fine tune the timing on race engines.

    Oil

    To keep all the rotating parts moving freely, oil is pumped through little tunnels or galleries in the block and head which feed the crank, con rod, cams and valve stems. The oil pump is usually driven off either the crank or the cam and has a pressure regulator and an oil filter to ensure a steady and clean supply of oil. Using the right oil makes a difference to power and reliability.

    Stay cool.

    The explosions generate a hell of a lot of heat, in fact its enough to melt the engine. So coolant, usually an equal mix of glycol and water flows through hollow passages around the cylinders and cylinder head, especially round the valve seats, to let the coolant take the heat away to the radiator. The whole lot is pumped round fairly slowly by the coolant (water) pump.

    So there it is, an engine. Simple in principal but tricky in the details.

  • Lying cars

    Why your car is lying to you.

    We rely on some of the things a car tells us, like speed for instance, in order to stay safe and also to stay on the right side of the law. So it might be odd to hear that many things a modern car tells us are in fact quite deliberately wrong.

    Here’s an experiment for you if you have a flash car; look at the trip computer, fill the fuel tank then make a note of ‘distance to empty’ or ‘range’, and after a long drive when its nearly zero make a note of ‘average MPG’ too. When you fill the tank you can work out the real MPG. What you will probably find is that the reported MPG is rather optimistic, but its not because the system is inaccurate, modern systems are really rather good at being accurate. Most systems are very precisely over optimistic by up to 10%, although I have seen certain Teutonic luxo-barges be out by 20%. Obviously this is to ensure the customer feels better about their consumption of the earth’s natural resources.

    The range calculation has a different story to tell. Again it can be very accurate, but because some customers ‘chance it’ it says zero when the car still has a few miles left in it. This is more a matter of self preservation than conning the driver, if a modern car runs out of fuel all sorts of bad things happen such as catalyst or fuel pump failure. But if you are driving consistently you will probably find that when range has gone down by 10 miles you have in fact actually travelled 10 miles.

    Now here’s the funny thing, if anyone actually compared the MPG and range info they would see the two don’t tally. But of course you would have to be pretty bored to do that.

    You probably know the speedo always reads slightly higher than the real speed, but do you know why? Many years ago when gauges were made of brass and springs, they were not very accurate which is a problem if you don’t want to be arrested for speeding, so laws were introduced to tighten things up. The law had to allow for the inherent inaccuracies of the measurement method, in the UK this means the gauge is allowed to read anywhere between the true speed and 10% higher, but because there are variations in accuracy due to production tolerance manufacturers tend to play it safe and aim for the middle of the allowable range. So most read 5% over.

    But again the gauges don’t agree with each other. On most cars the odometer is fairly accurate, so if in that remarkable moment of boredom you where to divide the change in mileage by the time taken you would find the true speed. Although to be fair it would be a lot easier to look at a GPS unit.

    Other gauges take an even greater liberty with the truth. Years ago some cars had oil pressure gauges, readings were read with the same intensity that a fortune teller reads tea leaves, often adverts for second hand cars read something like ‘good oil pressure’. But oil pressure can vary between one engine and another as they trundle off the production line, there is nothing wrong with this; some engines last a lifetime with really low pressure. Unfortunately some owners became a bit paranoid about the minute flickerings of that little gauge and sent their cars back, so drastic measures were taken. For instance if you bought one of the last Jag V12s the oil pressure gauge was in fact only connected to the pressure switch and a resistor, so as soon as the engine started it stayed pointing resolutely at the middle of the range, very comforting. They were by no means the only manufacturer tackling the problem imaginatively. But as soon as computer controlled dash instruments hit the main stream in the 90’s the standard method became to make all the gauges read something nicely reassuring unless there was an actual real problem that needed the driver to take action.

    Its the same with the temperature gauge, as the real engine temperature fluctuates the gauge reads a nice steady ‘normal’ and only climes out of its comfort zone if the car thinks it’s in immanent danger of exploding.

    Now, you might feel rather cheated by all this, but actually for most drivers its probably for the best. If you don’t happen to understand that oil pressure and coolant temperature do vary a lot then you might get quite anxious as the gauges dance about. By only alerting the driver when there is a genuinely something to worry about allows them to concentrate on driving but still take action when necessary. And if the speedo reads a little high then you wont get flashed by cameras if you stray a few MPH over the indicated limit.

    So although its lying to you, it means well.

    Mostly.

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