Pontiac Bonneville low oil pressure

1990 Pontiac Bonneville with 3800 engine. After driving several hours, pulled into traffic and wound the engine up a little to about 3000 rpm
maybe. Noticed the oil light on and no pressure on the gauge. Shut it down checked the oil etc. Started it back up and didn't hear any rattling or clanking. Revved it up to around 2000 rpm and the oil light would just go out and the gauge would just move. I had just had the pressure sender replaced before we left so I thought it was probably a bad sender again. Drove it home with the oil light on all the way, about 100 miles in the sticks. Took it to a garage at home and he put a regular gauge on it and found about 3 lbs at idle and about 15 lbs at 2000 rpm. Normal pressure should be around 40 lbs.
The 3 lbs. and 15 lbs. oil pressure was with the engine not fully warmed up. Before this happened the pressure gauge would be right at mid scale when running on the highway and not drop at all at idle. After it warmed up well the gauge would show a little below midway at highway speeds and drop slightly at idle.
The sudden drop to 3 lbs happened all at once. The car has only 60 thousand miles on it and the oil was just changed a few hundred miles ago.
Any thoughts where to start looking?
Thanks! Gary
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I'd say you're pretty well going to have to look at the bottom end bearings and the oil pump. Sometimes it just doesn't take much to wreck one.
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I've heard of oil filters causing problems like this. It wouldn't take much to try a new one of good quality.

bearings
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well my bet is on the bearings are shot

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The first thing I did when I got back was to put another new oil filter on. No difference.
Thanks Gary
On Thu, 4 Jan 2007 20:58:07 -0800, "Scott Buchanan"

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Gary Schafer wrote:

Any place that sells new engines. ;-)
You didn't mention the mileage. If it's over 150k, I wouldn't bother trying to decide if it was just an oil pump problem, cuz it's moot. GW
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On Thu, 04 Jan 2007 22:45:33 -1000, Geoff Welsh

It has only 60,000 miles and the car is in excellent shape but for the oil pressure problem.
I don't think it is worth a new engine though at that age.
Thanks Gary
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Assuming you had decent oil in it and drove it home "carefully" (no heavy acceleration, no high rpm, etc) then there's a pretty good chance that nothing got hurt. If it were mine, I would send an oil sample in for analysis before I spent any time or money trying to fix the oil pressure problem. If the oil analysis comes back without a lot of bearing material... you probably got away with it. In that case, just fix the oil pressure problem (probably a relief spring in the filter adaptor) and rock on. Perhaps have another analysis done at the next oil change to confirm that nothing is "coming apart" on you. I found this on another site,
"Titan has an "Engine Oil Analysis" kit sold at AutoZone stores. Ask for the "PPM" analysis instead of the standard "ABC" analysis as it is more detailed. Look for high silicon levels, wear metals, low TBN (reduced oil viscosity), and engine oil contamination, especially excessive fuel and glycol presence (sodium and potassium elevation). Connect with other owners to compare results. Do several analyses over time to show the changes."
There is info on the Titan kit at the bottom of this page, in case you don't have an AutoZone nearby: http://s2.pegasusautoracing.com/2006/066.pdf
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Titan Lab website: http://www.titanlab.com/content/inside/products/Oil.html
message

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Gary Schafer wrote:

A 1990 with 60K?!?!?! Are you the original owner?
GW
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On Fri, 05 Jan 2007 22:57:04 -1000, Geoff Welsh

No, I guess I am the second owner. Just got it this summer from some older people that went to a nursing home. I didn't get to drive it but a few hundered miles before the oil pressure problem. It ran fine and worked well when I got it.
Gary
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Gary Schafer wrote:

Hmm. If it's not making noise, I'd just drive it. You'll have to rebuild the engine anyway. GW
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GW wrote: A 1990 with 60K?!?!?! Are you the original owner?
GW, I'm the original owner of a 91 with 308,345 miles. Original oil pump too!!
harryface
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Harry Face wrote:

Duh. I've known you for five years. GW
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Harry Face wrote:

My 91 Regal has the same engine, btw, GW
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Well from what you are describing it sounds like the oil pump is blocked up or broken. I would bet that the bearing are shot too if the pressure drops to zero. From personal experience, if the car is not all rusted out, I would go buy a long block, pull the engine, and start with the new long block. Take all the parts off your old engine that you need to complete the install and have a new engine to drive with.
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Is the oil pressure verified, or is it just the factory guage showing zero? MANY GM "guages" are really a disguised "idiot lite" - they read "proper" pressure or zero. Put a master guage on to verify pressure if you have not already done so. What oil are you using? When was it changed? and a dozen other questions after those are answered.
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On Sun, 07 Jan 2007 20:37:31 -0500, clare at snyder.on.ca wrote:

I pasted the following from my original post where I tried to list what all happened. Yes a mechanical gauge was put on to verify the cars gauge.
Took it to a garage at home and he put a regular gauge on it and found about 3 lbs at idle and about 15 lbs at 2000 rpm. Normal pressure should be around 40 lbs.
The 3 lbs. and 15 lbs. oil pressure was with the engine not fully warmed up. Before this happened the pressure gauge would be right at mid scale when running on the highway and not drop at all at idle. After it warmed up well the gauge would show a little below midway at highway speeds and drop slightly at idle.
The sudden drop to 3 lbs happened all at once. The car has only 60 thousand miles on it and the oil was just changed a few hundred miles ago.
Thanks for any help! Gary
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On Sun, 07 Jan 2007 21:18:19 -0500, Gary Schafer

You didn't answer what oil. I would do a mild flush (put in some MMO for about 20 minites of idling, then dump the oil) and then put in a fresh fill of a good quality oil like Castrol 10W30 or 10W40 (preferred) and see what happens. I'm suspecting a gummed oil pressure relief or crappy oil (not Penzoil perchance?)
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On Sun, 07 Jan 2007 22:07:26 -0500, clare at snyder.on.ca wrote:

I don't know what kind of oil was put in at the oil change. I believe that engine calls for 5w-30 oil.
I know that people have their favorite oils but what is wrong with penzoil?
I had thought of the pressure relief valve being the culprit but I don't know these engines at all.
I guess it is worth an oil change and the mmo to see if that might do anything. How much of a job is it to pull the pressure relief valve out to check it?
Thanks Gary
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