1991 Regal multiple issues

[buickmastermind]

Okay, I don't have the time to figure out what the problems behind these symptoms are, so hopefully others here have had them and been able to get them fixed.

1. Gas mileage mediocre at best. 24 was the highest I ever got, and that was cruising the entire trip at about 85mph. Usually only gets 20-21 on brand new plugs and wires, even highway speeds of 60-70mph. A guy I work with has one, same year same engine, and he gets about 30-32 freeway going ~70-80mph. I noticed that compared to the 3.8l in my '86 LeSabre, this one doesn't have as much power in the higher rpm range and not as much as I think it should overall. Idle is starting to get a little unsteady as well, fluxuating between 600 and 750 slowly.

2. Oil pressure now exceeds 100 psi at cold idle according to guage. When warm, it's about 70. When cruising cold the needle is almost dead on 120 psi, and when it warms up it still hovers at 100 psi. Usually is between 40 and 80 depending on how I'm driving. Using the same oil as before, and I've ruled out the filter as the cause. I had noticed on occation a burning plastic smell from under the hood, and traced the cause to a small oil leak that seems to be coming from the head gasket and definitely leaks onto the exhaust pipe on the front. This was leaking/smelling longer than the pressure issue, but made more noticable by it.

3. A 195 degree thermostat is opening at 150 according to my temp guage. The fan switch sensor stopped working when I replaced it for turning the fan on and off every 3 seconds. The heater never seems to get warm on a cool morning ~35 degrees, but 10 degree differance in the outside temp to about 45 degrees will make it get really hot. I think that the control unit is messed up, as it won't light up with the rest of the dash lights and stereo lights.



So what it seems to me is that head gaskets are leaking, therefor compression is low. Also, the coolant temp is not being properly reported to the guage and likely the computer which may be causing a bad fuel mixture. This could explain the poor gas mileage. However, based on how smooth the engine runs I can rule out timing and spark quality, but can't verify that there is spark advance.

Thanks again,

[GTP Dad]

First of all I think the majority of your problems are related to the thermostat. If it is opening at 150 degrees then you need to replace it. The computer is reading too cold an engine and forcing it to run rich. That is also why you don't have any heat.

As for the oil pressure problem get a manual guage and check it. The oil pressure sensor may be bad and giving you false readings as it is if the pressure is truly that high you have a major restriction somewhere and are probably going to end up blowing one of the main seals.

If you suspect a bad head gasket, I would do a compression test to see what kind of compression the car actually has. If it is low then that could account for the decrease in performance.

Finally, the oil leak you describe is probably a valve cover gasket. Common problem and easily solved. Especially if it is leaking onto the exhaust manifold.