Contrary to many posts you may read, this is professional advice and you definitely should act upon what I have to say in this post, and not just because I am a mechanic with over 25 years experience but because it is logical and will save you a shit-ton of money (as you will learn if you carry on reading).

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What is Start/Stop Technology?

Maybe, like me, you drive round in an old banger and don’t have to deal with this troublesome automotive feature, or maybe you have this technology in your car and it has never worked (believe me, with this fickle system that is more likely than you think). Either way you may be someone who has no idea what Start/Stop is or what it does.

The Start/Stop system is built into modern vehicles and automatically turns off your engine whenever you come to a standstill, eg. While waiting at traffic lights or junctions. Under the right circumstances your engine will cut off, and then once a signal is received by the ECU, which could be a press of the brake/clutch pedal, the engine will restart. Without going into the finer details, this is how the Start/Stop system works.

Why do we have a Start/Stop system installed?

As with most engine related modifications you find on modern vehicles, the Start/Stop system offers no advantage to the performance or the comfort of your driving experience. In fact, the exact opposite is true. Worse still, is that this modern day requirement is only there for environmental purposes, which is all good and well for the polar bears but I very much doubt that these magnificent beasts will be replacing your broken inlet valves in an uncanny show of gratitude.

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Of course, the Start/Stop system is sold to customers by telling them it will raise their vehicle’s fuel economy and subsequently save them money. Now the fact that your engine isn’t running while at a stand still makes it hard to deny that the driver is saving money. I mean, if the car isn’t consuming fuel then that must be true, right? Well, maybe so, but I’d say the pennies you’re saving by those momentary pauses are massively outweighed by the astronomical costs you’ll eventually incur because of the damage that is being done to your engine…

Damage? What Damage?

Before we get to the most destructive consequences of the Start/Stop system, let’s begin with the indirect effects it has on your engine.

Modern day vehicles are governed to an absurd level when it comes to the emissions they put out and manufacturers are in a constant battle between performance and emission control. Some of you will remember the emissions scandal that Volkswagen became caught up in a while back and this was solely due to the fact that when you create cars with emission controls, such as EGR(Exhaust Gas Recirculation) and DPF(Diesel Particulate Filter), you sacrifice performance. Volkswagen knew this and instead of sacrificing the performance of their vehicles they decided to fake their test results to make the cars look as if they were going green while somehow increasing their power output. Obviously this pissed off some other manufacturer and whoever that was decided to blow the whistle on VW. Seven years on and Volkswagen are still paying out compensation for this deception.

Before I digress any further, let’s get back on track. So, what’s all this have to do with Start/Stop? Well, especially when it comes to diesel cars and DPF, but also with petrol cars and EGR, the vehicle needs desperately to get up to temperature to work efficiently. DPF relies on high temperatures to burn away the carbon atoms and when this is not achieved they produce soot, you know, that sticky black substance that used to keep so many chimney sweeps in business. EGR valves will only send exhaust gasses back through your engine when temperatures are high enough, but still, when the vehicle isn’t up to temperature or suddenly cools down that soot is going to build up and begin clogging up the EGR valve itself. It’s no wonder why they sell EGR blanking kits for most vehicles on eBay. Likewise, when the DPF isn’t running at optimum temperature or suddenly begins to cool down the soot will build up and over time your DPF will become completely blocked up. Of course, the DPF has what’s called a regeneration process to help clean itself, but this isn’t always going to work and when it fails you’ll probably be non-the-wiser until it’s too late. And by the way, to replace your DPF costs many hundreds of pounds, if not thousands depending on which car you own.

So, let’s consider someone who runs a vehicle in the morning to take their children on a relatively short journey to school. I imagine that much of this journey will take this person through their local town or village and mainly be along small roads with many junctions to navigate through. Do you think this constant cutting out of an engine while stopping at traffic lights and junctions is going to assist in getting it to its optimum temperature? Of course it isn’t! And now you see the first problem with using your Stop/Start feature. Not so keen on going green now, are you? Personally, I think you’d do less harm if you sat at each junctions with your foot to the floor thrashing the bollocks off your engine. At least then your engine will get up to temperature and begin burning the fuel at its most efficient level. And just as an interesting little foot note before we move on, did you know that a perfect working combustion engine would exhaust nothing but water and nitrogen? Only trouble is, there’s no such thing as a perfect working combustion engine. Not yet…

So, we’ve covered the indirect affect of the Stop/Start system which is bad enough, but you wait until you read about the direct affect that Stop/Start has on your vehicle…

The most important part of your entire engine, the one thing that you must ensure you never neglect, is the timing belt or timing chain.

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Whether you have a chain or a belt doesn’t matter, this part does exactly the same job and as the name suggests that job is to keep your engine in time with itself. Now, bare in mind that you have at least 3 large cylindrical hunks of metal(aka your pistons) constantly moving up and down at mind-boggling speeds within your engine chambers. And now imagine that at precise moments there are little metal valves that need to open up to allow fuel in the the chamber and to allow exhaust gasses to escape. The timing of this process is crucial, not only to allow for correct and efficient combustion, but also to ensure that a valve doesn’t open at the wrong time, which would result in the piston colliding with the valve head and destroying your engine.

(Gif created by @omotorshow)

Without a correctly installed and well maintained timing belt catastrophe would most definitely be the outcome. However, there are always times when your timing belt/chain are under stress and in danger of failing. A weak, damaged, or old timing belt is highly likely to snap or at the very least loose some of its teeth. In either scenario this will result in your engine pulverising itself. As for a timing chain, it isn’t often you’ll get one to snap, but that doesn’t mean it can’t be stretched. A stretched belt may not lead to a complete destruction but it can certainly allow for your cam or crank sprockets to move out of time by a tooth or two. The results of jumping a tooth may not add up to belt valves but it will still lead to an disabled vehicle and a costly visit to the local garage.

I hope this helps you to understand how important your timing belt/chain is and why it should be treated with the utmost care. And with that in mind, I will now explain why your Stop/Start system is in direct conflict with this important rule…

Any mechanic who knows what they are taking about will tell you that the most likely time you timing belt will fail is when you turn the key to start your engine. This is because the force required to rotate and engine is at its highest when the engine is motionless. Think of it like pushing a car. Once the car is moving it’s quite easy to keep it moving, but to actually get it to move to begin with takes a much greater effort. Your starter motor has to overcome this same problem when starting the engine. And just to labour the point, take a look at the label on your car battery the next time you open the bonnet(or “hood” if you’re from the USA). You’ll see that on your battery there is a sticker which details the power of your battery. In one section it will state the CCA(Cold Cranking Amps). You’ll notice that this number will be in the hundreds, somewhere between 300A and 900A depending on the size of your engine. This amperage is drawn by the starter motor from the battery to turn your engine over fast enough for it to be able to fire up and begin the combustion cycle. As you see in the diagram below, the amperage being drawn by the starter motor is at its highest during the first few moments. After this the engine is rotating and momentum allows for much less effort to be required.

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Being that the starter motor acts upon the flywheel which is directly connected to the crankshaft sprocket, you can appreciate the force that is initially applied. This force is then transferred to the camshaft sprockets via the timing belt and this initial effort to get the engine rotating is what puts the timing belt/chain under it biggest strain. Now, for those who have been following this, you will understand that increasing the number of times you start your vehicle from stand still increases the number of times your timing belt/chain is at its highest risk of failing. In the case of a timing chain this simply shortens the lifespan of the chain due to the increased strain on its links which inevitably causes it to stretch.

It is said that on average a typical engine can handle around 50,000 start up cycles. The Stop/Start system in modern vehicles can increase this count to 500,000…

That’s a pretty big increase, don’t you think? And with manufacturers still quoting the same lifespan for the timing belt and timing chain replacement intervals, it’s left to you, the owner, to evaluate when to replace this integral part of your vehicle. But more importantly, it’s up to you to decide whether or not you switch your stop/start on or off. The choice is yours…

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Thanks for reading and while you’re still here I’ll take this opportunity to tell you about my beer quiz! I’m giving away 10 Hive to the winner and the quiz prize rolls over each #beersaturday! So come on and test you knowledge 🍺