If you have been told your car has a “wet belt”, you are not alone in wondering what that means. It is one of the most common questions we get, usually from drivers who have just seen an oil pressure warning or read a worrying headline. Here is the short version, without the jargon.
A timing belt that lives in oil
Every engine needs its camshafts and crankshaft to turn in perfect time with each other. On many engines a toothed rubber belt does that job. Traditionally it sits on the outside of the engine, behind a plastic cover, and stays dry. That is the conventional cambelt most people have heard of.
A wet belt does the same job but runs inside the engine, permanently bathed in engine oil. Some engines also use a wet belt to drive the oil pump, separate from the main timing belt.
Why do manufacturers use them?
Running the belt in oil reduces friction and noise, and it can be packaged into a smaller, lighter engine. That helps with fuel economy and emissions figures, which is why wet belts appeared on popular engines such as the Ford 1.0 EcoBoost and the PureTech 1.2 used by Peugeot, Citroën and Vauxhall.
So what goes wrong?
Rubber and hot oil are not natural friends. Over the years the belt softens, swells and starts to break down. Short journeys make it worse, because the oil never gets hot enough to burn off moisture and fuel, and those contaminants attack the rubber. Using oil that is not to the manufacturer’s specification speeds it up too.
As the belt degrades it sheds fragments into the oil. Those fragments are carried round the engine and collect on the oil pickup strainer, the mesh that the oil pump draws through. As the strainer clogs, oil pressure falls. Eventually the engine is starved of oil, or the belt itself jumps a tooth or snaps. On most of these engines that means serious damage and often a replacement engine.
How do I know if my car has one?
The easiest way is to use our wet belt checker, or browse every make and model. The most common examples in the UK are Ford EcoBoost and EcoBlue engines and the Stellantis PureTech engines. If you are still not sure, send us your registration and we will check it for you.
What should I do about it?
- Know your interval. It is set by the engine and is usually given in years and miles, whichever comes first.
- Use the right oil and stick to the service schedule. Good oil is the best protection the belt has.
- Do not ignore warnings. An oil pressure light, a rattle on start-up or black specks on the dipstick all deserve a call.
- Have it replaced properly. A wet belt change should include cleaning the sump and oil pickup, not just a new belt. Here is what a proper wet belt change involves.
Replacing a wet belt on time costs a fraction of a new engine. If yours is close to its interval, or you simply do not know, it is worth finding out now rather than when the warning light comes on.