What are 'wet' timing belts and why are they bad?

What are 'wet' timing belts that I hear are being used in cars recently and why do mechanics not favour them?

Tom Nelson (Maynooth)

Nov 2025 Filed under: timing belt or chain

---

Expert answer

Hi Tom,

A traditional 'dry' timing belt, mostly made of rubber, runs in air behind dust covers. A 'wet' belt is of similar construction but actually runs in oil behind sealed covers. The theory is that this reduces heat, friction and noise while enhancing reliability.

Unfortunately, the material of the belt can be damaged by contaminants in the oil itself, causing premature failure of the belt or other engine damage caused by bits of the belt clogging up other components.

Not every car that has a wet belt has an issue, but they certainly have a bad reputation.

Shane O' Donoghue - Complete Car Advisor