Reducing Damage to Wet Belt Systems

Timing belt in oil systems, also known as wet belt systems, have been around for over 15 years. Vehicle manufacturers such as Ford, PSA, and Volkswagen use them. Wet belts are fully encased within the engine, whereas ‘dry’ systems are positioned outside of the engine crankcase. Wet belt systems were introduced to reduce the weight of components, reduce the engine size, maximise efficiency and meet emissions targets.

How can a wet belt system be damaged?

• Oil impurities such as soot and other oil oxidation breakdown debris can get between the belt teeth and pulleys, weakening the belt.
• Wear on the outer belt coating exposes the underlying materials directly to the oil, which may contain unburnt or partially combusted fuel that attacks exposed belt materials.
• The teeth can become detached, creating a smooth section on the belt. This causes the pulley to slip and changes the engine timing.
• The side wall of the belt being exposed to oil and oil debris can cause delamination of the belt layers.

Any failure from the belt that creates belt wear debris can cause problems elsewhere in the engine, due to blocked oil pathways, particularly in the oil pick up strainer. This would trigger a low oil pressure warning.

Ways to reduce damage

Belt design

Teeth: The initial design of wet belt systems featured a straight cut tooth design profile. Over time with greater knowledge and advanced manufacturing techniques, the teeth now have a curved design. This makes the teeth less susceptible to wear, improving durability and ensuring a quieter operation of the belt.

Belts: Manufacturers make timing belts from rubber or an elastomer such as nitrile, neoprene, or polyurethane, and they include reinforcing cords to control the belt tension. They also tend to have an oil resistant coating to improve durability, resulting in a longer lifespan than belts found in older vehicles.

Elastomer testing

To reduce the impact of oil on the elastomers used throughout the engine, elastomer testing is now a requirement in many vehicle manufacturers’ oil specifications. PSA have a 1,000 hour test, VW have a 500 hour test and Ford have a 168 hour test, using the material used to manufacture wet belts. Automotive engine oils are also designed to meet these strict requirements in real world driving conditions.

What can you do about it?

Use the correct oil

Ensure that you always use the lubricant specified by the manufacturer for your vehicle, taking into account the viscosity (oil thickness) and the recommended specification to meet the requirements of the engine. To make an informed decision tailored to your vehicle, rely on comprehensive product information, expert advice, and the convenient Millers Oils WhichOil? Oil checker tool which is designed to make the oil selection process as simple and hassle-free as possible. Read more here.

Lower oil drain intervals

The vehicle drive cycle has an impact on the oil drain interval. If the drive cycle is severe, a shorter oil drain period should be followed. This includes: driving short journeys, stop-start driving, carrying and pulling heavy loads, or long periods of idling. In our experience, the oil drain interval should be halved. Ignoring draining intervals, means less oil on the timing belt, degrading the lubricant and shortening the lifespan of the belt.

Reduce belt replacement intervals

Vehicle manufacturers all have different recommended replacement intervals ranging from 100,000 km to over 150,000 km. Some workshops and dealerships are now recommending shorter replacement intervals as belt failures are occurring at much lower mileages.

How to detect issues with the wet belt system

• There is no obvious indicator in the oil to detect issues with the wet belt. However, if the wet belt is wearing, the engine may be difficult to start or is likely to misfire, idle roughly, and perform erratically at high rpm.
• On some vehicles it may be possible to visually check the condition of the belt by viewing through the oil filler and looking for signs of cracking.
• PSA have a tool, which you can purchase online, that measures the width of the belt to check for swelling, which would indicate that the belt needs replacing.
• Further examination would require the removal of the oil sump for a closer look at the belt and other parts of the engine.

Proper maintenance and development of wet belt systems is crucial to reducing damage. These systems offer advantages, particularly in terms of meeting emissions targets, however, various factors can cause damage to the belt and engine. It is vital that the correct oil specification is always used, the oil level is maintained and the vehicle manufacturers recommended oil drain period is never exceeded, and if possible reduced. This applies whether the vehicle is in the warranty period or not. If in doubt always consult a workshop or dealership for direct advice and avoid obtaining anecdotal advice from the internet.

Click here to use the WhichOil? Oil Checker Tool

Oils with specifications requiring the respective OEM elastomer test:

XF Premium Engine Oil C5 VW 0w20

XF Premium Engine Oil C2 ECO 0w30

XF Premium Engine Oil C2 0w30

XF Premium Engine Oil C3 VW 5w30

XF Premium Engine Oil C3 VW 0w30

XF Premium Engine Oil C2 5w30

XF Premium Engine Oil ECO 5w30

Our in-house Technical Support Team are always happy to discuss any further questions you have.

Call on: 01484 475060

Or e-mail at: technical@millersoils.co.uk

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