Oil Pressure Concerns


Old 01-09-06, 12:08 PM
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Oil Pressure Concerns

Got some GREAT help over in plumbing, so I'm here in Automotive for more guidance.

I've got a '98 Jeep Cherokee Sport (6 cyl) with a 120,000 miles on it. The thing has always run good (bought it used 5 years ago with 48k on it), but I'm noticing the oil pressure guage acting strange lately. Here's the story:

40 psi is mid-guage. I noticed a MUCH lower reading after warm-up when I switched to high mileage oil. Not being a techie, I might expect this with thinner oil...mechanic said it was nothing to worry about. I've been fine running like that for approximately a year.

About a month ago I had driven for a while, all ok, then stopped and turned off the engine for several minutes. At startup I got a "check engine" light and noticed ZERO oil pressure! I turned the engine off and re-started...the light came on again, but a quick rev of the engine and I got some pressure. I was concerned enough to have it looked at. Mechanic said it was probably the sensor (I read online where they'll reflexivley replace those and that it often IS the sensor) and, given the age and miles I let 'em replace it and had 'em change the oil (Penz high mileage 10/30). My guage remaind low (as it has been at idle since I started using the high mileage) but the light didnt' come on again...until two days ago...very same scenario. It's also time for another oil change.

So, to make a long story short, my pressue is fine while I'm driving (up to around 40 PSI) and drops to just under 10 at idle when the engine is warm; however, where as before the pressure ALWAYS increased when I "gave 'er the gas", I'm noticing now that sometimes the guage is actually reversed and decreases when I rev up. I know that high pressure isn't always something to be too concerened about, but LOW pressure is bad...very bad. I need to keep driving this thing for another year or two if at all possible, so I'm wondering what I should have done/replaced/looked at.

All thoughts are welcome!
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Old 01-09-06, 02:16 PM
Join Date: Nov 2005
Location: North Carolina
Posts: 948
you most likely have an electronic gauge. i hate them. if it were mine i would have your mechanic install a mechanical gauge under the hood. (less work than inside the vehicle) and observe the results. many older engines will show less at idle because of increasing clearances, but at higher rpm's the oil pump can compensate
Old 01-09-06, 02:46 PM
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Join Date: Jan 2001
Location: Kansas City, Missouri.
Posts: 1,172
You will need to measure the pressure under the hood to see if the pressure is really low or not.

If it is, then, uh, mmmm, heck, just for fun, call your local auto parts store and ask if they have the oil pump "on the shelf" at the store. The auto parts industry has a keen insight into what parts to stock and what parts to keep at the warehouse. I would just be curious to hear their answer.

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