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2002 Pontiac Bonneville High Oil Pressure

My Pontiac also has oil on the engine now with the oil pressure at 120. It started at 40 then went to 60. I had the oil changed and they put 5w30 which they were not supposed to do. I wanted 10w30.

Is this a common problem with Pontiacs? Is there a non engine replacing solution? Will I have to tow it to the mechanic?

The electronic the gauges in modern cars are not always trustworthy. Either the electronic gauge or the sending unit on the engine could be faulty.

The first thing I would do is to have a mechanic hook a proper test gauge to the engine block to get the true pressure that the oil pressure is under.
If he finds that it is still high …then you can discuss the problem further.

As far as the oil change shop putting in 5W30 rather than 10W30 will make no difference. If the engine has over 150000 miles the 10W30 may help but only slightly.


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Thank you for responding. I’m glad it is not my fault, because it was my Maamaa’s car.

They may have installed a defective oil filter when they did the oil change.

The oil filter has a by-pass valve that allows some of the oil to by-pass the filter media. If this by-pass valve is stuck closed, the oil pressure will go thru the roof.


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If the oil pressure is indeed that high I would suspect a scored passage in the timing cover where the oil pressure relief valve is located causing the relief valve to hang up and not relieve the pressure when it gets too high. If that were the case I would expect the oil filter to be blown apart from so much pressure.

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I believe that 5w-30 is the correct oil for that car. Why did you want 10w-30? The usual reason for going with a heavier oil is to increase oil pressure, which is not what you’re looking for, I imagine.

I agree with @Yosemite and @Tester. A faulty sender or oil filter are the most likely causes.

Looks like stepper motors are used in the cluster, the motors are prone too eratic readings, as suggested get a real oil pressure check, if it is ok you can pay $500 for a new cluster and programming, replace all the motors yourself, like 25 bucks, or send the cluster out for $75 or so to replace stepper motors. If your GM is like mine, the oil pressure guage only creates an estimated oil pressure, and there is an idiot light for low oil pressure. Best of luck!

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Agree. Get the real pressure checked then proceed from the results-new gauge, relief valve, filter as determined.

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This is a stock vehicle, right? No racing-style oil pumps installed?

Yes. It is a stock vehicle.

I concur w/the others, absent any other symptoms, probably just a dashboard gauge problem. A shop oil pressure gauge would test that. Next in line is the gadget that regulates the oil pressure in the outflow of the oil pump. Before going down that line though, make sure you are working with clean oil of the correct spec and an oem oil filter.