oil pressure drops when sitting with foot on brake - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 04-07-2005, 08:31 PM   #1
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Default oil pressure drops when sitting with foot on brake

:(
Ok in the morning I have great pressure over 40 psi on my gage,after car is hot and you stop at a light with your foot on the brake the reading drops to almost the red line,car has 153k miles and other than lifter ticking runs great. I run 10w30 but did run 5w30 with the same results ?? thanks
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Old 04-07-2005, 09:04 PM   #2
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Yes, it will. This is a natural result of aging internals and isn't much to worry about.

If you plan to keep the car, start saving for a Targetmaster short block or begin planning for a rebuild.
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Old 04-07-2005, 09:14 PM   #3
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And thank the Bonnie god for letting your gauges work... I'm dying of old age waiting for my new cluster to come in so I can tell heat and oil pressure. Not sure if the old fan relay is working. Works on ac...lol
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Old 04-08-2005, 04:30 PM   #4
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run a 20-w50 oil since summer is coming.

On super sloppy engines, I've run 20w50 castrol with two cans of stp. It keeps a 318 going that I have in a truck... it is so loose on the main bearings that if you came down a steep hill and take your foot off the gas, the oil pressure goes up 10-15 lbs. Yes, it was that bad 10 years ago and yes, its still running. 4.10s and no OD will wear an engine out big time.
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Old 04-08-2005, 07:33 PM   #5
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My grandfather'* bonneville did the same thing. Its a '95 with 120,000 miles. I poured 1/2 can of seafoam into the crank, and drained the oil about a month later. Problem gone. Pressure does not really drop below 40 psi ever. I think that these engines are real sludge monsters, but the seafoam cleaned it up. Slowed his oil consumption down considerably also probably by freeing up the oil rings. I seriously suggest you at least try this so that you don't have to rebuild as soon.
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Old 04-08-2005, 09:42 PM   #6
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Quote:
Originally Posted by BillBost37
Not sure if the old fan relay is working. Works on ac...lol
Both fans, or just one? I think one of them is used mainly by the cooling system when the temperature sender kicks it on; the other runs whenever the A/C comes on.

Somebody around here was an expert on those fans (Fuddy, maybe?). It ain't me...
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Old 04-09-2005, 01:56 AM   #7
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Acg....No more fan problems. BTW both come on fast when you kick the a/c.

Buzzed up and hung out with my best buddy...aka mechanic Dan. He let me borrow Fisher Price til Sunday night. (Fisher price is the secret identity of his really expensive Snap on Scanner)

Needless to say I was able to see real temps...my fans kick and work just fine. No problems....no worries...just ignoring that red zone and depending on computer to tell me check gauges if something serious happens until new gauges arrive.
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Old 04-09-2005, 04:01 PM   #8
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Quote:
Originally Posted by sputnik767
My grandfather'* bonneville did the same thing. Its a '95 with 120,000 miles. I poured 1/2 can of seafoam into the crank, and drained the oil about a month later. Problem gone. Pressure does not really drop below 40 psi ever. I think that these engines are real sludge monsters, but the seafoam cleaned it up. Slowed his oil consumption down considerably also probably by freeing up the oil rings. I seriously suggest you at least try this so that you don't have to rebuild as soon.
Sludge monsters...??

I have yet to see a 3800 beat the crapp out of any oil, thats unless these engine didn't have many oil changes which will kill or make a mess of any engine...

And at 138,000 miles on 10w-30 oil I still cold start at 80 psi, and hot idle at 35-40 psi... I have never used any cleaner in the engine... Just routine oil changes...

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Old 04-09-2005, 04:49 PM   #9
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Originally Posted by jr's3800
And at 138,000 miles on 10w-30 oil I still cold start at 80 psi, and hot idle at 35-40 psi... I have never used any cleaner in the engine... Just routine oil changes...
Me, too, at 115K right now. I change oil and filter (Valvoline 10W-30 and AC filter) every 1500 miles, which for my car works out to about every 4-6 months. Absolutely no problems with oil pressure, no leaks, no gunk, nothing. The oil is dark when I change it, but it'* not black.

I would say if you can't remember when you changed it last, or if you just bought the car used or whatever, change oil and filter now, then do both again after 500 (five hundred) miles. It'll be black already; trust me on that. After 500 miles, do it once more. Again, it will be filthy black already, but by this point the engine will be running smoother, and your next lot of oil won't go black anywhere nearly as quick.

Let the detergents in the oil do their job, and as the oil picks up the dirt and keeps it in suspension for filtering, a couple of short term changes like this will help get the worst of it completely out of the system. In 1000 miles you'll have removed a large portion of what took 100,000+ miles to accumulate, so as you can see, it'* pretty easy to get ahead of the curve on sludge buildup, and then stay there.
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Old 04-09-2005, 08:36 PM   #10
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Well, when he bought the car it had about 112,000 miles on it, and the guy who had the car before seemed to take good care of it. He was an older guy and had his own mechanic and everything. Anyways, we change his oil about every 6 months which works out to be about 2500 miles, and the oil comes out black. During that time period he has to add about 1.25 quarts of oil to maintain his oil level (no visible leaks so its probably burning due to stuck oil rings), and his oil pressure dropped into the red zone when stopped at a traffic light. Now, after I used SeaFoam, the pressure and burn-off seems to have improved. That is what led me to believe that these engines tend to sludge up. Now, i've never dropped the pan on that car to look.
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