Dear Tom and Ray:

I have a 1985 Buick Somerset. Everytime the coolant gauge reaches the mid point between cold and hot, the oil light comes on. If I then stop and turn off the car, it won't restart. Meanwhile, the temperature gauge continues to slowly rise while I sit there, approaching, but never reaching the "hot" mark. The oil level is correct. Can you explain this? Rosa

Ray: Sure we can, Rosa. You've either got low oil pressure or--if you've led a good, clean life--just a bad oil pressure sending unit, which is just a switch.

Tom: Here's what happens. When the engine heats up, the oil naturally thins out. That lowers the oil pressure and makes the light come on. You--appropriately--stop and shut off the engine.

Ray: When the engine is turned off, the cooling system also shuts off, so heat continues to build up in the engine for a while (this is perfectly normal).

Tom: But on this car, the oil pressure switch is connected to the electric fuel pump. And when the switch indicates low oil pressure (whether there actually IS low pressure, or the switch is just broken), the fuel pump is automatically shut off to protect the engine. That's why you can't restart the car right away.

Ray: So you've got to determine whether you really have low oil pressure. And the best way to do this is by getting an oil pressure test.

Tom: If the pressure is good and all you have is a bad switch, you should get down on your hands and knees and thank your lucky stars for your incredible good fortune.

Ray: If the oil pressure is actually low, you should get down on your hands and knees and pray that you got to it early and all you need is a new oil pump.

Tom: If a new oil pump won't fix it and the engine is kaputski, then you might as well get down on your hands and knees anyway and pray for a good finance rate from your Buick dealer. Good luck, Rosa.

How can you tell if a used car is in good condition -- or even OK, for that matter? Find out by ordering Tom and Ray's pamphlet "How to Buy a Great Used Car: Things That Detroit and Tokyo Don't Want You to Know." Send $3 and a stamped (55 cents), self-addressed, No. 10 envelope to Used Car, PO Box 536475, Orlando, FL 32853-6475.

© 1996 by Tom and Ray Magliozzi and Doug Berman Distributed by King Features Syndicate, Inc.

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