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Carbon lies?
I have a 1996 SAAB 900SE 2.3 turbo convertible with only 56,000 miles from new and serviced once every year by a SAAB dealer or SAAB specialist. A report on the latest service this week says that a common problem on these engines is complete failure due to carbon particles in the oil, that happens when the sump strainer gets a sludge build-up due to the pick up pipe being very close to the sump. As this is a common problem, the garage says they always pass some used oil through a muslin to check when doing oil changes too look for the carbon particles. As the particles were found It is therefore recommended that the car is taken back as soon as possible and the sump is taken off and the strainer cleaned. There is never any need to top up between services. Have you heard of this on these engines and do you agree this is reasonable preventative maintenance or is it padding out the bill?
Asked on 29 August 2009 by
Answered by
Honest John
I can understand it. Did no one ever tell you about 'simmering' a petrol turbo? A turbo on a petrol engine can get red hot. Literally glowing. If you switch the engine off when the turbo is red hot, the turbo vanes continue to turn as they spool down and the engine oil that both cools and lubricates the turbo bearings carbonises. You should never switch off a petrol turbo engine when the turbo is red
hot, which it will be after high speed running, after running on the
motorway, after a long ascent, and after towing. After this sort of running, you should always idle the engine for a couple of minutes before switching off, as that will both cool and lubricate the turbo bearings. Alternatively, if your journey ends with low speed running
for 5 - 10 minutes through a town, that will do the job and you will not
need to simmer before switching off. You must also always use 'fully' synthetic oil in the engine. If sumps are drained by siphoning old oil from the dipstick tube instead of by adding a flushing oil to the hot oil and removing the sump plug, the sticky mess in the bottom of the sump will remain there and lead to the sump strainer problem you describe.
hot, which it will be after high speed running, after running on the
motorway, after a long ascent, and after towing. After this sort of running, you should always idle the engine for a couple of minutes before switching off, as that will both cool and lubricate the turbo bearings. Alternatively, if your journey ends with low speed running
for 5 - 10 minutes through a town, that will do the job and you will not
need to simmer before switching off. You must also always use 'fully' synthetic oil in the engine. If sumps are drained by siphoning old oil from the dipstick tube instead of by adding a flushing oil to the hot oil and removing the sump plug, the sticky mess in the bottom of the sump will remain there and lead to the sump strainer problem you describe.
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