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Have you got a wet belt under your bonnet?


YOU may think from the headline that this article is about some sort of fetish, but no, it’s about something nasty which could be lurking inside your car engine and about to destroy it with little or no warning.

This so-called innovation has been introduced relatively recently by car manufacturers to reduce costs and fuel consumption, and shave carbon dioxide emissions by a few grams per km. But it could lead to a complete new engine or replacement car far earlier than would otherwise be necessary. Has anyone considered the ‘carbon footprint’ of that?

I consider myself to be mechanically minded, but I had not heard of ‘wet belts’ until last week when my neighbour’s fairly new and expensive (but out of warranty) car had its engine destroyed when its wet belt ‘failed’. This nearly reduced him to tears, so I did a little research and found that this was a far from an isolated case – see here, for example. 

Let me enlighten you as to what this is all about. First I need to cover some basic car mechanical stuff, but I will try to keep it simple. If you have a petrol or diesel car it has pistons in the engine which go up and down. These are connected by a ‘crankshaft’ which lives near the bottom of the engine. Air (and sometimes fuel) which the engine needs for combustion is let into the engine using valves which are located at the top of the engine. There are more valves which let the burnt gases out. These valves are operated by another shaft called the ‘camshaft’. The crankshaft and the camshaft need to work together so they are linked by a rotating belt or chain called the cambelt or camchain.

Here is a link to a more detailed explanation.

A camchain lives inside the engine; it is very strong and normally lasts the life of the engine. You will usually never know anything about it except when it may rattle a bit as the engine is nearing the end of its life. A traditional dry cambelt lives outside the engine, is easy to inspect and is replaced during regular servicing, perhaps every five years or so. Replacement is normal and adds perhaps £300-£700+ to your service bill. Not nice, but tolerable.

About a decade ago, some manufacturers started using a drive belt, running in oil, located not outside the engine, but inside it. This is a consumable component (ie it may need replacement), hidden from view, difficult to inspect, and with catastrophic consequences if it fails. And they do!

The theory is that the belt should last ten years or perhaps 150,000 miles, which is the life of the engine. But many, like my neighbour’s, fail early (and sometimes as low as 30,000 or 40,000 miles) with huge costs for the car owner. An engine rebuild can easily cost £5,000 or more.

There are three main ways these belts can fail:

1)    The belt could snap while the car is being driven (like a traditional dry timing belt). This would mean that in some engines (not all) the pistons would smash into the valves, requiring the cylinder head to be rebuilt with new valves (this is known as an ‘interference engine’). The repairs will be very costly, but not the end of the world.

2)    The second failure mechanism is far more sinister. The belt can degrade and break up over time. As it is running in the engine oil, the bits of belt can contaminate the oil or block the oil strainer which lives in the sump at the bottom of the engine. The engine is slowly starved of oil, destroying components like the turbocharger, camshaft, crankshaft and bearings. This will require a complete engine rebuild.

3)    The third mechanism is a combination of the two: the belt slowly degrades, starving the engine of oil, and then catastrophically fails stripping its teeth and smashing up the pistons and valves. This is pretty fatal for the engine.

Don’t forget that this is all made worse because the belt is hidden away inside the engine. Gradual failure can go undetected until it is too late.

A lot of cars fitted with these ‘wet belts’ are now coming up to ten years old and the belt will need replacing even though the engine may be running well. This means dismantling the engine at a cost of perhaps £1,500 or £2,000+ on what is now an older car. A most unwelcome bill, just to save a few mpg or for the car to have very slightly reduced emissions.

While writing this article, I had huge difficulty in finding out which engines have these hidden horrors. Ford used them in their ‘EcoBoost’ engines fitted in a wide range of vehicles from Fiestas to Transit vans. Peugeot and Citroen have used them in a wide range of models using the 1.2 ‘PureTech’ engine. I could find some references to them in Honda engines too, but I am sure there are others.

A quick look at the Honda Fixed Price Repairs web page reveals an entry for the replacement of the Civic 1.0L timing belt for an eye-watering cost of £1,703! However £1,703 is cheap compared with a destroyed engine. (It would be interesting to hear of readers’ experiences.)

So if your car is out of warranty and you intend to keep it, and it has one of the engines mentioned above, you need to find out if it has a ‘wet timing belt’ or ‘belt in oil’ and when you need to have it changed. If you are buying a used car with one of these engines you may find that the current owner or dealer is selling it because the ‘wet belt’ is shortly due for replacement and it is better to sell the vehicle and avoid the huge service cost.

Finally, don’t confuse the problems detailed above with traditional dry timing belts. These have been used for decades and although they can fail with catastrophic results, they live outside the cylinder block of the engine and are inspected when your car is serviced.

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Matt Terry
Matt Terry
Matt Terry is a lecturer specialising in safety / environmental law, environmental science and wider environmental issues.

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