Car Talk

January 1990

Dear Tom and Ray:
I own a 1984 Toyota Corolla Sedan. The dashboard light for what I think is the amount of oil comes on between gearshifts. There is no evidence of leakage, and I just had the oil and filter changed. What could be causing this?
Michael

TOM: That light does not measure the amount of oil in your engine, it measures the oil pressure. It's possible to have plenty of oil--so the dipstick reads full--and still have no pressure to circulate the oil. If you've been driving around with no oil pressure, Michael, I hope you've been saving your Green Stamps.

RAY: If you've ever tried to clean a frying pan after you've cooked something with no oil, you know what your pistons and cylinders feel like after driving with no oil pressure. You should definitely have it checked right away, but don't assume the worst. A number of simple things could also cause the oil light to come on. We've seen a zillion Toyotas (actually 4 or 5) with faulty oil switches--that's the switch that operates the oil light. If that's all it is, that's a $20 job.

TOM: One other unlikely possibilities come to mind since you just had an oil and filter change. If your brother-in-law did the oil change, he may have accidentally drained out the transmission fluid and added four extra quarts of oil to the crankcase. That would mean you have 8 quarts in there.

RAY: That would make the moving parts of the engine come in contact with the oil--causing it to foam. The oil pump can't pump foam, and again, you'd have no pressure. If that's the case, you'd better hope your brother-in-law has been saving his Green Stamps 'cause he's going to owe you an engine.

Beat up old car

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