I have a Buick Somerset Everytime the coolant gauge reaches...

Dear Car Talk

Dear Car Talk | Apr 01, 1996

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?

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

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.

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