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Questions and Answers

A Hot Cougar

Q. Hello Vincent, I have a 1991 Mercury Cougar LS 3.8 liter V-6 with 140,000 kms. It's an auto transmission with fuel injection. My question is concerning an odd overheating problem that continuously occurs.

Approximately 6 months ago we (my sisters boyfriend with help from a licensed mechanic) replaced my head gaskets because they were obviously blown. When we started it up it had a rough, vibrating idle and the check engine light comes on randomly through a drive. That wasn't happening before.

That's not really my concern because it is now stalling out frequently when ever I come to a full stop and try to accelerate. Didn't have problems with that until after the "repair". That too is not my concern, just a little background information.

My main concern is the overheating, it will overheat, or say it is and I'll turn on the heat to full and it'll blow out cold air. It will just spike up all of a sudden to hot while I'm driving. I'll take my foot off the gas pedal and let it cruise along and it will calm down to just above mid range. I then just nurse my car around for a bit and it will eventually start blowing hot air again and drop down to near cold. What's going on with my car Vincent? I have no clue.


P.S. (My fuel gauge sometime goes up to full even when it's close to empty in reality and my speedometer sometimes gets stuck and doesn't work properly. Could maybe my cars temperature gauge just be lying to me? I don't really want to risk it.)

A. As for the fuel gauge, if you car was built between 6/1/91 and 6/30/92 the problem is probably caused by a distorted fuel tank. If the distortion can be confirmed then you will need to replace the fuel tank. If not, the most likely cause is a bad sending unit.

As for the temperature gauge, if it reads HOT and cold air is being blown out, you do not have enough coolant in the system. I would make sure the coolant is topped off and the cooling system bled of all air. I'm assuming they put a new thermostat in when they did the head gaskets. If not, go ahead and replace it. It may be sticking.

You might want to look at the temperature sending unit. If the number is less than 2774, replace it. That run of sending units was bad. Any unit with the number 2774 or higher are okay.

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