Maintaining belt in oil (BIO) timing belt

Car manufacturers have been under immense pressure to reduce CO2 emissions and increase their cars' fuel efficiency. This has introduced innovations and complications, which include split cooling systems to facilitate speedy warm-up times, variable displacement oil pumps to reduce drag and timing belts that run in oil within the crankcase.

What is a BIO timing belt?

A Belt In Oil timing belt system comprises a kit of parts including tensioners, idlers and a fibrous belt that runs inside the engine. They provide an easy way of reducing CO2 emissions. Our earlier blog on the topic provides more information.

What goes wrong with BIO belts?

As with conventional timing belts that run outside the engine, the BIO belt can fail, resulting in severe mechanical engine damage. Yet, particles are breaking off the main belt, before total failure. These particles circulate around the engine, until they restrict the oil pump inlet, starving the engine of lubricant and resulting in higher wear levels. They also can affect the braking system, too, so check your make-and-model for any resultant safety recalls.

Do short journeys and low mileages wear out BIO timing belts?

Yes. Engine oil that has been contaminated with petrol poses a serious threat to BIO longevity. This is a particular problem with cars that are used on short start-stop

trips, especially when their engines have had little chance to reach their normal operating temperatures. One BIO belt manufacturer told us that a 5% increase in petrol within the oil reduces BIO life by 30%, because this contamination produces abrasive crystals.

How can I prevent BIO failure?

While many people blame poor design, owner neglect can be a factor in premature BIO timing belt failure. Therefore, GEM recommends that all owners of BIO-equipped cars take precautions, by following our top tips:

Check your manufacturer for updates

Enquire with your car manufacturer about your BIO belt change interval, especially if it has been revised, since your car was built.

Such intervals are set by time and mileage - do not exceed them and conduct whichever interval comes first, even if your car has a low mileage.

Never ignore warnings

Attend to any warnings, regarding low oil levels. Should your low oil pressure lamp flicker, or illuminate, stop driving immediately and have the engine checked.

Never allow the engine oil to drop below the 'minimum' level on the dipstick. Low oil levels cause the oil to overheat, hastening BIO degradation.

Engine oil that contains incompatible additives can attack the BIO. Use oil only that meets the carmaker's specification code, details of which will be in your handbook, or service schedule.

Never skip servicing, especially oil changes

Engine oil quality is vital to BIO reliability. It must be changed on time. Again, time and mileage intervals will be specified; carry out the service whichever arrives first.

We have heard of incompatible oils being used to save money, to the detriment of BIO life. Again, make doubly sure that the manufacturer-approved oil is used.

Check also if any belt checks are required at service time. For instance, certain Peugeot/Citroën 1.2-litre engines in the PureTech range require that the belt thickness is measured with a special tool, to check for excessive swelling.

You can also check the BIO visually. Remove the oil filler cap and inspect the belt, as pictured. It should possess a shiny black surface. A rough, cord-like texture, such as that pictured, especially if accompanied by cracks, indicates that the belt structure is deteriorating and depositing particles into the engine. Consult a garage for advice.

Should you be looking to buy a BIO-equipped car, negotiate hard on the purchase price, if it has less than perfect service history, including engine oil changes, or walk away.

What BIO timing belt should I buy?

We have heard that BIO belt specifications continue to evolve. Therefore, buy the latest belt kit you can, which will incorporate all of the latest enhancements.

What extra work is required, when changing a BIO timing belt?

Like conventional timing belts, you do not change the belt alone. You must replace ancillary parts that are supplied in a kit. These include tensioner and idler pulleys. We recommend that you change any ancillary belts, too.

Yet, as BIO belts reside within the engine, you should have any trace of old belt particles removed. This involves removing the oil sump and, possibly, the oil pump

and turbocharger strainers, and cleaning/renewing them. This is in addition to any extra operations that either your garage, or your carmaker, deems essential to obtain maximum engine life, after the belt is replaced.

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