A wet timing belt is a timing belt that stays submerged in engine oil and synchronizes the crankshaft and the camshaft. This page covers what that belt is, why the oil matters, how a wet belt fails, and how the service decision is made. It applies to engines whose maker specifies a belt running in oil.
It is often called a wet belt or a belt in oil. Not every engine has one, so check the owner’s manual.
Key Takeaways
- A wet timing belt synchronizes the crankshaft and camshaft while submerged in engine oil.
- Not every engine has a wet belt; the owner’s manual says which drive an engine uses.
- A dry timing belt must stay clear of oil. Oil can delaminate it or snap it.
- Use the oil grade and specification in the owner’s manual, and change the oil on time.
- Mileage figures differ by source. The maker’s service information for the specific engine decides.
Table of Contents
- What a wet timing belt is
- Wet belt versus dry belt
- Why the oil matters to a wet belt
- How wet belts fail and what the signs are
- How to inspect a wet belt
- Replacement interval and service
- If you are sourcing dry timing belts
- FAQ
- About Longyi Rubber Products Factory
What a wet timing belt is
A wet belt is a timing belt, also called a cambelt, that synchronizes the crankshaft and the camshaft and is submerged in the engine oil. A conventional cambelt doesn’t run in that oil. It is also called a wet cambelt (RAC on wet belts).
The same technology is also called a wet belt, an oil pump drive belt or a belt in oil (Tomorrow’s Technician on oil system (belt-in-oil) belts). A timing belt in oil is the timing application of that technology. A wet belt does the same timing job as a dry belt: it keeps the crankshaft and the camshaft in step.
Belt in oil is used in two applications: a timing belt, and a belt that turns the oil pump. The same US trade source reports these belts in Asian, European and domestic engines, including diesels.
Wet belt versus dry belt
A dry belt must stay clear of oil. Oil contamination has been a death sentence for a traditional timing belt because of its rubber and fiber construction. Oil attacks the rubber and the raw edge, where fibers are exposed, until the belt delaminates or snaps (Tomorrow’s Technician on belt-in-oil timing drives).
Compared with a conventional cambelt, running in oil helps reduce friction, engine noise and fuel consumption, and wet belts are increasingly popular in new cars (RAC on wet belts). Belt-in-oil belts are described as more temperature-resistant and less prone to stretching than conventional dry belts because of improved materials (Tomorrow’s Technician on belt-in-oil timing drives).
Belt-in-oil makers claim up to a 30% reduction in friction loss compared with chains or dry belts, which can increase fuel economy by a little more than 1% (Tomorrow’s Technician on belt-in-oil timing drives). That is a maker claim.
Why the oil matters to a wet belt
On a wet belt engine, oil is the fluid the belt runs in. Wet belt engines need the exact oil grade and specification the manufacturer recommends, which is in the owner’s manual (RAC on wet belts). Using the wrong oil leads to issues with the belt and the engine.
OEMs have changed oil specifications to protect these belts, and oil or additives that are not approved can cause the belt to swell and degrade (Tomorrow’s Technician on oil system (belt-in-oil) belts). The quality and condition of the oil affect how long a belt in oil lasts. Missed oil changes, or running past the recommended interval, can leave oil that no longer protects the belt. Leave an unapproved additive out of the oil.
If oil changes are neglected, the degraded oil cannot protect the belt. When the elastomers and fibers break down, the teeth can separate from the backing cords, and ignoring the oil life monitor can end with the belt shredding itself (Tomorrow’s Technician on belt-in-oil timing drives).
Oil can be contaminated and diluted by unburned fuel that reaches the crankcase through misfires or a leaking high-pressure fuel pump, and short drive cycles can leave condensation in the oil (Tomorrow’s Technician on oil system (belt-in-oil) belts).
How wet belts fail and what the signs are
The usual failure is teeth breaking off the belt, and these belts rarely snap (Tomorrow’s Technician on oil system (belt-in-oil) belts). On a timing drive, lost teeth can set correlation codes and cause valve damage. On an oil pump drive, missing teeth can stop the pump turning. Broken teeth end up in the oil pan and can clog the oil pickup.
When a belt is damaged, the debris goes into the crankcase. The oil filter traps small pieces, but large chunks can clog the oil pickup in the pan, causing low oil pressure and starvation at higher engine speeds (Tomorrow’s Technician on belt-in-oil timing drives).
As a wet belt ages, rubber particles can get into the oil and cause further problems, potentially serious engine damage. RAC on wet belts links premature wear to lack of servicing, incorrect oil, poor maintenance and constant high temperatures.
Wet belt signs of failure named by these sources are:
- A low oil pressure warning light will likely signal an issue with the wet belt.
- Debris in the oil: small particles in the drained oil and rubber particles as the belt ages.
- Timing or correlation codes, with a risk of valve damage on a timing drive.
How to inspect a wet belt
The belt sits behind a cover, so the practical checks are the oil and any inspection point the maker provides. Tomorrow’s Technician on oil system (belt-in-oil) belts says the belt is hidden behind a front cover or the oil pan. Some makers made it visible through the oil filler cap or an inspection cover. If you can see the back, cracks, delamination or other damage on the back are grounds for replacement.
Look for small debris particles in the drained oil. Use the oil filler cap or the inspection cover when the engine has one.
Check the owner’s manual or the manufacturer’s website to learn whether the car has a wet belt and how often it should be serviced and replaced. RAC on wet belts gives that instruction, and not all cars use one.
Replacement interval and service
The wet belt replacement interval is set engine by engine. Tomorrow’s Technician on oil system (belt-in-oil) belts gives up to 150,000 miles for some belts, and the service interval depends on the manufacturer. Check the service information for the engine and the operating conditions.
RAC on wet belts gives up to 100,000 miles and up to a decade for many belts. That figure depends on the vehicle manufacturer and on how well the engine has been serviced. The maker’s service information for the specific engine decides.
Wet belt replacement is not a minor job. Replace all seals and gaskets, because oil leaks after replacement are common, and extra labor is needed to seal the front cover or the oil pan. The camshafts and the crankshaft still have to be locked. The biggest installation error is not reviewing the installation procedure in the service information (Tomorrow’s Technician on oil system (belt-in-oil) belts).
For a dry timing belt the logic is different, because oil damages that belt; the timing belt replacement interval page covers it.
If you are sourcing dry timing belts
This page is about belts in oil. For a dry automotive or industrial synchronous belt, send LYBELT the belt code, drawing or size. The timing belt tensioning guide covers tension for a dry belt, and timing belt squeal causes and fixes covers noise. If the code uses an HTD profile name, see the HTD timing belt meaning page.
FAQ
What is a wet timing belt?
A wet timing belt is a cambelt submerged in engine oil that synchronizes the crankshaft and the camshaft, unlike a conventional cambelt. It is not a conventional dry cambelt.
How is a wet belt different from a normal timing belt?
A dry belt must stay clear of oil, because oil attacks the rubber and the exposed fibers until the belt delaminates or snaps. A wet belt runs in oil, which helps reduce friction, engine noise and fuel consumption compared with a conventional cambelt.
What are the signs of a failing wet belt?
The signs are a low oil pressure warning light, debris or rubber particles in the oil, and correlation codes with a risk of valve damage. Teeth break off and can clog the oil pickup, and these belts rarely snap.
How often should a wet timing belt be replaced?
It depends on the engine. Some belts are rated up to 150,000 miles (Tomorrow’s Technician on oil system (belt-in-oil) belts), and another source says many last up to 100,000 miles and up to a decade (RAC on wet belts), so follow the maker’s service information for your engine.
Does the engine oil matter for a wet belt?
Yes. Use the exact oil grade and specification in the owner’s manual, or the wrong oil can swell and degrade the belt. Neglected oil changes let the teeth separate from the backing cords.
Can you inspect a wet belt without taking the engine apart?
Sometimes. If your engine has an oil filler cap or an inspection cover that exposes the belt, check the back for cracks or delamination; damage there means replacement. If the belt is hidden, check the drained oil for small debris and read the owner’s manual, because not every car uses a wet belt.
Sources
- RAC on wet belts
- Tomorrow's Technician on oil system (belt-in-oil) belts
- Tomorrow's Technician on belt-in-oil timing drives
Source names appear here only as references. LYBELT is not affiliated with them.
About Longyi Rubber Products Factory
LYBELT is the brand of Longyao County Longyi Rubber Products Factory (General Partnership), based in Longyao County, Xingtai, Hebei, China, and making rubber belts since 1999. The factory holds IATF 16949 and ISO 9001 certification and works from 130+ rubber compounds.
The range covers automotive, industrial, agricultural, ATV/UTV and motorcycle belts. For OEM and ODM orders, belts are made to the customer’s part number, drawing or size, with private label and packaging. Email: luxin@lybelt.com.