my oil presher drops - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-22-2007, 04:00 AM   #1
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So I have a problem. when my engine heats up my oil presher drops when my car is at a idle but when im driving its fine. Is it my oil pump, I went to go pick 1 up and the guy at Napa send theses oil pumps donít go bad. Can eny 1 help me. My trany went out and I already poled my motor and Trans out. I got my new trany but donít know what to do about my motor and its oil presher. In sted of my normal 5w30 I tried using a 10w30 and it was no better. My car is a 92 SE hellp?
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Old 03-22-2007, 04:29 AM   #2
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What are the readings you're getting at idle, and while driving? Try to notice what pressure at what RPM'* while you're driving, if you can. Just want to see how much of an issue we have here.

You say you switched from 5w30 to 10w30. Was that a complete oil change and filter change? If you haven't changed the oil filter, may want to do that. Then cut your filter in half and take a picture of it to post here if you can.

When you removed the 5w30, what did the oil look like? Any wierd discoloration at all? Any water or antifreeze in it?
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Old 03-22-2007, 05:05 AM   #3
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My car idles at like 900rpm give or take now when its hot and im at a stand still for over like ~30sec it drops and u can hear the lifters start to nock ever slitily. Now what the pressure was at when its itild down is ~15-25, It also happens if I just let off the gas and coast a ways. Than when I take off at like 1500-2000rmps and up its just fine the pressure is like ~80. About my oil I had strait 10w30 in it last filter and all. I drained my oil last week when I poled my motor and Trans out and all my fluids were fine, besides my burnt trany fluid but thatí* besides the point. The oil was always fine, defiantly no antifreeze just the brown from mileage on the oil between changes.
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Old 03-22-2007, 05:47 AM   #4
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well something that could be tried is some kinda engine flush, or some kerosene in the crankcase, something to clear out any gunk that might have built up. If that is not it I'm not sure. But that would be my suggestion.
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Old 03-22-2007, 08:17 AM   #5
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The pumps in the 3800 are driven by the crank and are such that as Napa mentioned, they don't really go bad. It'* a great system.

Oil pressure is created as oil is forced through the crank and out the bearings and other bearing areas. The only pressure regulating item in the car is behind the oil filter adapter. The spring and slide regulate pressure based on spring pressure.

With the motor out, this would be an easy item to inspect and possibly replace. The oil filter adapter gasket (to my knowledge) is only available at the dealer or performance places like Intense/ZZP. Cost is ~$2.50 for the gasket.
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Old 03-22-2007, 06:50 PM   #6
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Try what BillBoost said.
Otherwise, -how many miles are on your car?
This type of symptom is typical of a worn-out engine, and you're pushing 15 years on yours. You might just have a worn-out engine. The problem will only get worse with time, however your car might remain drivable for some time even with this situation. My wife'* old 88 Grand Prix 2.8L V6 continued driving for a few years on 20W50 oil. Ultimately it blew a head gasket and I had a new engine put in it.

A compression test on your cylinders can give you some indication of worn rings & cylinders.

For your 3800, your options would include rebuilding your existing engine, or getting a remanufactured or new engine, or a used engine at a salvage yard.

Also, and this is a long shot, your oil pressure sending unit could be wonky, but if not, then it'* just doing its job and showing you the actual oil pressure problems that are typical of a worn out engine.
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Old 03-22-2007, 07:05 PM   #7
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While a compression test might point to wear.. the oil pressure is not reliant on the rings/compression.
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Old 03-22-2007, 07:07 PM   #8
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Quote:
Originally Posted by Bugsi
Try what BillBoost said.
Otherwise, -how many miles are on your car?
This type of symptom is typical of a worn-out engine, and you're pushing 15 years on yours. You might just have a worn-out engine. The problem will only get worse with time, however your car might remain drivable for some time even with this situation. My wife'* old 88 Grand Prix 2.8L V6 continued driving for a few years on 20W50 oil. Ultimately it blew a head gasket and I had a new engine put in it.

A compression test on your cylinders can give you some indication of worn rings & cylinders.

For your 3800, your options would include rebuilding your existing engine, or getting a remanufactured or new engine, or a used engine at a salvage yard.

Also, and this is a long shot, your oil pressure sending unit could be wonky, but if not, then it'* just doing its job and showing you the actual oil pressure problems that are typical of a worn out engine.
This doesn't seem as likely for a 3800. My '93 had over 225,000 miles on it, and the oil pressure was just fine. And I'm definitely not an isolated case. There are plenty of cars on this forum with high mileage that doesn't have low oil pressure.

That'* why we love these engines, they're darned near bullet-proof. I would almost bet that what BillBoost mentioned will be the case.
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Old 03-22-2007, 09:57 PM   #9
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Quote:
Originally Posted by TrueWildMan
This doesn't seem as likely for a 3800. My '93 had over 225,000 miles on it, and the oil pressure was just fine. And I'm definitely not an isolated case. There are plenty of cars on this forum with high mileage that doesn't have low oil pressure.

That'* why we love these engines, they're darned near bullet-proof. I would almost bet that what BillBoost mentioned will be the case.
I'm in agreement that these engines often go a very long time with little to no wear; there have been plenty of reports here from people that have torn down their high-mileage engines and the cross-hatch hone marks are still visible on the inside of the cylinder walls. But despite your 93 going 225,000 miles with your oil pressure fine, this guy is reporting fluctuating oil pressure readings. If the pressure readings are actually accurate, instead of being the result of a failure in the measuring and indicating instruments, the number one cause that I am aware of for fluctuating oil pressure in a car is a worn engine block, and that'* what I want to make him aware of. It might just be exactly what it'* indicating.
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Old 03-22-2007, 11:53 PM   #10
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Worn bearings on the crank, as Boosty pointed out, is more likely to be the problem, if not the other cause that he mentioned. A worn block will affect compression, but will not affect oil pressure.
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