low oil pressure - 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 07-06-2004, 04:18 PM   #1
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Default low oil pressure

Okay, this one is a head scratcher.


My car works relatively fine (beside it'* little ticks that im ignoring) when i drive in the morning. By the time i drive it home, i notice that my oil pressure and battery voltage are corrolary to the RPMs. That is, if i dont keep it above 3000 than my pressure drops to right above the red. On a normal day in the past it would hold just above 40 and not ever really move. Also my battery generally runs right around 14 volts, but will drop to somewhere around 12.5 when the oil pressure thing is goin on.

Some enviromental notes... its been HOT here and my engine temp has been higher than usual.

Other Notes, my cars A/C doesnt work (one ofthe problems im choosing to ignore). I hooked up a scanner and only pulled the code p0406


any help would be appreciated


THANKS
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Old 07-06-2004, 06:52 PM   #2
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When you mention battery voltage, are you talking about the voltage shown on a stock gauge inside the car? If so, I would suggest using a good secondary voltage meter right at the battery to see if it is in fact dropping to 12.5 volts. If it is dropping, then you most likely need an alternator. You should always have 13.5-14 volts or so when running. The low voltage may be affecting the gauges such that the oil pressure reads lower than it really is. Or you might have two distinct problems, because when hot, the oil pressure will drop down with low rpms.
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Old 07-06-2004, 07:03 PM   #3
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that is exactly the problem i had, the deal is the alternator as stated above was bad in mine and when the alternator would stop charging it would slow the oil pump and would also cause the gauges to fall.
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Old 07-06-2004, 07:05 PM   #4
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The oil pump is run directly off the crankshaft, the alternator can't make it run slower or faster.
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Old 07-06-2004, 08:03 PM   #5
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I'll bet the low oil pressure is caused (or at least aggravated) by the hotter engine temperature. Oil viscosity is sensitive to engine temperature, and when the oil gets thinner, the pressure drops. Without the extra fan that automatically comes on with the AC, these cars can actually run hotter without AC than they do when the AC is running. Once the oil pressure has fallen below the point at which the relief valve opens, it is also normal to see the pressure rise and fall with the engine speed and therefore the speed of the oil pump.

If your car has a lot of miles on it, consider switching to a higher viscosity oil. Straight-weight oils offer the best protection against heat breakdown. That'* why racers use straight 50 weight. I run Valvoline straight 50 Wt in my VW van, keeps it very happy under hot, high-load conditions. And that engine works a lot harder than these 3800'*. A less severe change would be Shell Rotella T 15W-40.
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Old 07-07-2004, 11:05 AM   #6
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I will be getting the Alternator bench tested today, i will post my results. I did JUST change my oil with 10w-30 (full synthetic mobil -1). So i might wait a little before checking that.


-Thanks for the help

EDIT: if i do need a new alternator, this would be number 2 in the past 2 years. last time it died completely and i ended up towing my car to autozone and fixing it in their parking lot. This time i may have some time to buy a good alternator. Any recommendations (keep in mind my sound system -- in my sig)
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Old 07-08-2004, 09:50 AM   #7
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Update:

Alternator is fine i took it in yesterday afternoon and there was no problems with it. I'd like to explore the heavier oil option. Does anyone have a suggestion. Im currently using synthetic, so if i could get a heavier synthetic that would be preferred.

What it looks like is that eventually my oil pump is gonna go. Is it worth putting the heavy oil in, or should i just replace it now--and can anyone tell me if thats something i could/should do myself


thanks
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Old 07-08-2004, 12:05 PM   #8
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Default oil pressure

Try a higher viscosity oil as mentioned.
I don't know if you have room for it on a 94 but I installed the longer Delco
PF-52 filter on my 96 and it seemed to boost pressure around 5 psi.
Every little bit helps.
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Old 07-08-2004, 03:19 PM   #9
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What is the oil pressure when you first start up in the morning? If you can verify that the pressure is low when the engine is cold, you've got mechanical problems-oil pump if you are lucky, bearings if you are not. The pump is an integral part of the timing cover and not particulary cheap or easy to replace, but compared to changing bearings, is a piece of cake. Some better mechanics on this site might be able to tell you whether an oil-pressure relief valve stuck open might cause your symptoms. I have never heard of it, but it seems like a theoretical possibility.

If the pressure only falls when you get over 200F, then I would suspect that temperature is a big part of the problem. You might want to consider a couple of cheap and easy options to lower the temperature. I think I have read on this site about wiring the AC fans so you can turn them on whenever needed. (Willwren might have done this?) The other thing would be to install a cooler running thermostat, as many on this site have already done. Eliminating excess heat is always gonna be good for your engine.

Makes me wonder if the performance of an alternator can be affected by high engine temperature?
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Old 07-09-2004, 02:34 PM   #10
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a Tstat is a good idea, i will be heading down to see if i can pick one up today. Im still curious if anyone can reccommend a good 40-50wt oil.


thanks for all the help
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