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I am driving a 1995 Bonneville and, lately, whenever I am idle, at a stoplight for example, my oil pressure drops and my check engine light comes on. Any ideas on why this could be happening?

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What color is the check engine light? –  Larry May 31 '11 at 18:58
It is the standard orange color. –  Gryphoenix Jun 1 '11 at 13:32
Check the codes if you have a code reader, or take to a local parts store that will do it for free. I asked to color because some vehicles have a "check engine" or "check gauges" that is usually red in color and is basically an idiot light. The light you described sounds like the check engine light that is turned on by the ECM and should have a code associated with it. With all that being said, I am not aware of low oil pressure turning on that light, so you may have more that one problem, or at least a different problem. –  Larry Jun 1 '11 at 13:43
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2 Answers

Sounds like your oil pressure is dropping at low RPM, which could be one of the following: low oil level, a bad oil pump, low viscosity oil, or worn bearings.

First step after checking the oil level is to check the oil pressure with a manual gauge.

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I've also seen this happen with Mobile 1 synthetic oil in a newly rebuilt Volkswagen Vanagon (water cooled) engine. Switching to a traditional oil solved it. I suspect what you are listing is much more likely, but wanted to throw it out there. –  Sean Reifschneider Jun 1 '11 at 7:15
I will do that, thanks! –  Gryphoenix Jun 1 '11 at 13:34
@Gryp you don't need an expensive pressure gauge, I just have an aftermarket oil pressure gauge I bought from a parts store. One like you would add to a car, most come with multiple adapters and can be used on many cars. –  Larry Jun 1 '11 at 13:47
To expand on the low viscosity statement, your owners manual will specify what viscosity oil to use in your vehicle and some (like mine) has a chart that shows what to use for different ranges of ambient temperature. The viscosity are the numbers you see on the bottles (5w30, 5w20, 10w30, 20w50, etc) When going from winter to summer months, I have to move to a heavier weight oil to keep my pressure up and engine properly lubricated. If I used that same oil in the colder months, it'd be like sludge. –  ManiacZX Jun 1 '11 at 23:29
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May even be a failing oil pressure switch...

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