Low oil pressure in 87 GW

[mattski]

Hello, my 87 GW with a V8 gets normal oil pressure of ~40 psi until it it warms up. Then at idle, the pressure drops to 0 and increases to 30 when I rev the engine. I plan on rebuilding the oil pump tomorrow. I am thinking to also check the pick up screen but if that was clogged, I would expect the pressure to increase once the oil thinned out.

Any thoughts on my approach and problem?

Thanks in advance.

Matt

[joe]

For one thing these gauges aren't very accurate in the first place. Second, oil pressure drops as the oil gets hot and thins out.
When it drops to 0 when warm/at idle are you getting any lifter noise? Does the eng temp go up significantly if it idles awhile? I would plug in a mech gauge first and see what your oil pressure really is...then go from there. Generally low oil pressure in these motors indicates worn cam and/or main bearings but if you're really getting 30 psi going down the road that's plenty(10 PSI/1000 RPM is fine). How many miles are on the motor?

[turtlejoe]

Checking/cleaning the pan and pick-up wouldn't hurt anything either, so at least you can check that off the list of possible issues. -joe is right, our stock FSJ guages are for entertainment only and there is no substitute for a good mechanical reading of what's happening.

I think it was the Preacher who was having a similar problem, and cleaning out the sludge in his pan and screen solved the issue.

[mattski]

The motor has 62k on it. I don't really hear any noise from it but I will double check. What kind of gauge would I use and where do I plug it into?

Other posts speak of the oil pump cover having some wear as a possible culprit for low pressure. I hope that you are wrong on the worn bearings.

[andy d]

its kind of a chicken and egg thing. low oil pressure causes bearing wear which causes low oil pressure. i would start by verifying the pressure with a reliable guage. then buff the oil pump cvr. then drop the pan and clean the pickup screen. BTW, the grey sludge on the bottom of the pan tells the tale, its bearing material

[jaz459]

does replacing the main bearing require a complete rebuild?

[mattski]

How do I check the oil pressure with a reliable gauge?

[Josh D]

Also, after checking the above items, switch to 20-50W oil and see if that makes a difference. A heavier oil really helps high mileage or high clearanced motors. Good luck!

[reddog]

It may be your sending unit for the factory gauge. 62K miles are not much assumming that you have a quality rebuild. No noise from the valve train is a good sign.

Was the timing cover replaced when the rebuild was done? The timing cover is also the oil pump body and being aluminum the pump body gets worn/scored with age. The oil pump on these things is sensitive to clearance on the pump cover and scoring in the pump body itself. When you pull the pump gears out check for said scoring in the pump body and the pump cover. You can try to cleanup any scoring with some wet/dry sandpaper and some type of flat material (inside the pump cover) and a thick glass plate with the wet/dry for the cover. Flatness is important. When reassembling the pump go with the tight side (the higher number - .006) of the clearance spec. Don't use any sealant on the pump cover. Only the correct gasket.

Kerry

[ December 06, 2002, 12:49 PM: Message edited by: reddog ]

[TheGossert]

I'd throw a can of STP in right away. That should increase your viscosity and bring your idling oil pressure to about 12 psi. It ain't great, but it's a good start.

Larry

[mattski]

The engine has not been rebuilt as far as I know, only the tranny. The 20-50 oil suggestion is good but I only use this vehicle in the winter to plow my road and I would be concerned with being able to crank over in very cold weather.

I am going to install a mechanical oil pressure gauge first ($10 plus my labor) and see what the true pressure is. If it is still low, then I will rebuild the oil pump and replace the pick up screen.

Thank you all for the advice and wish me good luck.

Matt

[Josh D]

Originally posted by mattski:
The engine has not been rebuilt as far as I know, only the tranny. The 20-50 oil suggestion is good but I only use this vehicle in the winter to plow my road and I would be concerned with being able to crank over in very cold weather.I live in Colorado and run 20-50W in my high mileage motor year round. It starts fine down to single digits. I haven't had to try it below zero yet. My 'rebuilt' engine will get 10-40W year round.

[mdill]

One problem on engines that only run for short periods during cold weather is that
the oil gets thinned out by the extra fuel from running on choke most of the time.
Change the oil often and go the next thicker muti-viscosity oil, that should help out.

Mike D.

[gwdawg]

My 87 GW was oil pressure was dropping down
to about 5psi, according to the factory gauge.
This after replacing the pump with the high
pressure Melling rebuild. At highway speeds
it was running about 35 PSI.

I just changed oil over to Shell 5w-40 semi-
synthetic and now at idle I'm getting about
15psi at idle and 45PSI at hiway speeds. I'm
sold. Granted at $12/gallon it ain't cheap,
but I like the insurance.