Watch for carbon build-up in Cadillac STS's piston rings

Q: I have a Cadillac STS 1999 4.6 L DOHC V8 with 97,000 km on it that I purchased about a year ago. My experience has been quite positive, save for the fact the engine seems to consume about 1 to 1.5 L of oil between scheduled oil changes. This vehicle is not abused and is driven with care.

Is more progressive oil consumption to be expected?

Technician Peter Lokun replies:

A litre and a half of oil between oil changes is well below normal oil consumption for this engine. With this fact in mind, there are no maintenance issues requiring attention.

This engine has a poor track record for oil consumption due to excessive carbon build-up on the piston rings. If your engine consumes more than a litre of oil per 800 kilometres, a decarbonization treatment is the usual remedy for this concern. This treatment involves adding liquid carbon remover into each cylinder and allowing it to soak for a period of time. Once the carbon is dissolved, the oil is changed to remove the additive and carbon.

An engine overhaul may be necessary only if the decarbonization treatment does not resolve the oil consumption issue.

In your case, the oil consumption results that you've quoted indicate your engine is in good health.

Inside information from experienced technicians indicate that this engine will build up carbon if babied.

With this in mind, don't be afraid to "put your foot into it" and get this engine revving when accelerating. As well, take your car for a good highway-speed run periodically.

Q: I have a 1994 Oldsmobile 88 with 224,000 km on it. It has a dual gas/propane engine. Who do I take it to for service?

Technician Peter Lokun replies:

You will have to find a technician qualified to work on your propane fuel system.

The Automotive Service Technician licence qualification in Ontario does not cover propane fuel systems with enough depth to qualify a "licensed technician" to install or service these systems.

To find qualified technicians, check the Yellow Pages or Superior Propane at 1-877-873-7467.

Service Centre technician Peter Lokun is an automotive instructor at Centennial College, Scarborough.

Email your mechanical questions to wheels@thestar.ca.

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