98 Bonneville, real low oil pressure - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 03-18-2010, 09:13 AM   #1
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Default 98 Bonneville, real low oil pressure

I found out that when you hit 10 psi the dash dinger goes off.

This motor had always been lower on oil pressure that the original motor but I never paid any attention to it. Going down the road it was just under 40 psi, idle was just above the red line. I always assumed that the gauge was wrong. Saturday I changed the oil and I added some Restore, Monday I drove the car 160 miles with no problem, Tuesday the pressure dropped to 5-10 psi at idle when warm. This motor has about 95k on it.

I replaced the pressure sender and the pressure is the same. When I removed the sender I got probably 2 spoonfulls of oil that leaked out and then it stopped. Is it possible that the pressure port is clogged?

The odd part is that even at 5psi at idle the motor runs fine and no overheating. I expected a day that this thing would die and I bought another car, this car is currently a backup, I'm just not ready to let it go. I'd keep driving it until it blows if it werent for the darn dinger driving me nuts. I'm just not sure that the pressure reading is correct.

This could even be an electrical problem, the other odd thing is that when I rev the motor I can see the check washer fluid and check gauges lights start to brighten up. They don't come on strong, it'* just kind of a ghosting in the background.

Last edited by hotrod53; 03-18-2010 at 06:02 PM.
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Old 03-18-2010, 09:57 AM   #2
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The only true way to know is with a mechanical gauge. Clusters can lie and gauges in the cluster can have bad contacts. Chances are that the bearings are wearing out though.
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Old 03-18-2010, 08:53 PM   #3
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My engine has 250K, but the same symptoms as yours. I've lost confidence plus the miles are high so it is coming out this w/e to start a bottom end & oil pump rebuild. The R&P is starting to leak & it is easier to get to with the engine out.
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Old 03-18-2010, 09:29 PM   #4
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Update: I removed the gauge cluster and cleaned and resoldered everything.... no change!

I'm going to throw some Lucas oil treatment at it just for fun.

This motor has already been changed, the tranny has 141K on it, it'* starting to rust and peal, it may be the ruination of the Bonneville....

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Old 03-22-2010, 09:37 PM   #5
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Update again: I removed the oil filter assembly to expose the pressure bypass valve. Everything in there was clean, I don't think that the bypass valve was stuck but its hard to tell. I did notice that there were some scratches in the side of the bypass valve so that at least indicates that it had bound at one time.

The gasket looks like it was glued as part of the replacement assembly that was used when the motor was replaced, it'* a real PITA to remove. I have is soaking in the parts washer and the local auto parts said that the replacement gasket was a dealer only item. I don't want to buy a new assembly since I'm thinking that this motor may be junk.
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Old 03-22-2010, 10:22 PM   #6
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Does you oil pressure drop, as the engine heats up ?. Example say Cold eng idle pressure say 40 psi then drops way down. I have 2000 Z-24 with a 2.4l and at cold Idle it 55 psi, then drop to 12 psi after 1/2 hr of running at 195 deg engine temp, (idle rpms 750 ). this is with a mechanical gauge. I have tried thicker weight oils and got hot eng idle pressure to 18 psi. But it'* funny how it take 1/2hr of driving a hot engine for the pressure to drop. I feel my problem is worn bearing or a pump ? but, it'* been this way for 30k and I drive this car on highway mostly, hot engine at 2500 rpm reads 37psi for pressure when I get off the interstate drops to 12psi at 750rps , the minute the engine hits 1200rpms i am over 25psi.
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Old 03-22-2010, 10:44 PM   #7
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This engine has always had just above the red at worst and as high as 38. Lately it drops to 5-10 when it warms up just like you said. I have no knocks or taps but that dinger will drive you crazy every time I come to a stop sign. 10 psi sets off the dinger.
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Old 03-25-2010, 07:49 PM   #8
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UPDATE: reinstalled the oil filter assemble and bypass valve, no difference. Removed the oil pan and checked the pickup tube and gasket. I then removed the pickup tube and cleaned it in the parts washer and installed a new gasket, no difference.

I still have the problem of the oil pressure and volt meter dropping slightly with the increase of RPM and the check washer fluid and check gauges illuminating slightly the higher the RPMs get.

The crank and bearings all looked clean and there was no crap in the pan.

All that I have to do is put a mechanical gauge on it, I have to aquire a few parts and pieces first.
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Old 03-25-2010, 08:59 PM   #9
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Another Update: Removed all grounds connected to the fender, drivers side looked like ECU grounds, who knows what the passenger side was. I cleaned all and reconnected... no change.
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Old 03-26-2010, 08:24 AM   #10
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That kills my post in the other thread. .......whichis why we should probably have kept this all in one thread...
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