Engine oiling issue

[chevellejoe]

I am looking at buying an 87 GN. While driving the car I noticed the oil pressure to be low. 10psi at idle and will level off around 30psi while cruising. The motor has about 10k since a complete rebuild. It was getting 10psi for every 1000 RMP. I checked it up to 4000 RPM. Also the car was running hot, around 210 to 220. It has some motor work and a large front mount, so I figure a larger radiator will cure this and bring up to oil pressure. The owner stated the oil grade was 10w30 Mobil 1. Another issue is the pressure gauge shows a slow response when increasing RPM. I’m not sure if it is a mechanical or electric gauge. Anyway he took the car over to the shop where he gets all the work done (the shop is a very reputable Buick guy) and cut open the oil filter and changed the oil to a thicker grade 20w50 Mobil 1. The filter was clean, no signs of a bearing going. Any ideas of why the pressure has a slow response to the RMP increase? Thanks

 

[Just a Six??]

Worn oil pump gears? bearing clearanaces? As long as it goes up 10 psi per 1000 rpm thats good but 10 is low. Altho, GM figured the cutoff was 4 lbs. maybe the guage isnt great?
Since a rebuild I gotta wonder about bearing clearance?

 

[aminga]

It could be the gauge. I had an older VDO that read 10lbs at idle swapped it and it was closer to 15-20.

Still seems OK to me.

 

[earlbrown]

Sounds like a combination of sloppy pump coupled with potentially loose engine tolerances.

Even if the gauge is suspect, the needle should jump pretty quick when coming off idle.

Are you running a biggie oil filter?

 

[chevellejoe]

The engine builder said he clearanced the motor between .020 and .030. This was about 8 years ago and 10k miles. So he was just going off top of his head but he said it was to stock tolerances. The Gauge looks like an old VDO. I was figuring there may be some build up in the gauge pickup causing the slow reaction. As for the oil filter I believe its stock size. The pump has a plate. Thanks for the comments. I am going to bring my own mech. gauge and try that before i buy it.

 

[earlbrown]

If you mean .002~.003" on the rods and mains, there's the oil issues.

Stock specs are right at half that.

 

[chevellejoe]

Yeah lol, .002 and .003 thousandths. On my Small block Chevy I run between .002 and .0025 with no issues. 20+ PSI at idle with 10w40. All engine builders that I have spoken to like to run no tighter then .002 unless it’s a stock application.

I have found out it is a mechanical gauge with a copper line. The engine builder said the copper line has more restriction compared to the nylon line and that will cause the gauge to have a slower increase in pressure. Has anyone ever herd of that? I do understand a restriction will cause that, but is a 1/8 copper line a different size then the nylon and have greater resistance?

 

[earlbrown]

Does this GN have a small block in it?

 

[mikestertwo]

The first thing you will learn is these motors are not small block Chevys. They like tight bearing clearances .001-.0015. Copper line does have a smaller I.D than nylon line.

 

[chevellejoe]

Ok so since the bearing clearance maybe loose, it still doesn't explain the oil pressure to increase slowly compared to the RPMs.

 

[theCATman]

Everyone is so hung up on oil pressure.

Oil volume is WAY more important that oil pressure. Excessive oil pressure (more than 10 PSI/1,000RPM) does nothing other than rob power & put unnecessary stress on components.

A little loose on the bearing clearances sure won't hurt anything. As long as the pressure is 10/1,000 I wouldn't worry about it.

 

[Nick Micale]

Yeah lol, .002 and .003 thousandths. On my Small block Chevy I run between .002 and .0025 with no issues. 20+ PSI at idle with 10w40. All engine builders that I have spoken to like to run no tighter then .002 unless it’s a stock application.............

Most of the engines we build are in that range also, street engines on the tighter side, race engines on the higher number.

Race engines idle between 25-35 psi with a race filter, and 10-40 or 20-50 when in summer conditions.

Before anything is done to your engine, I would install a good filter like a Wix and change to regular oil like plain 30W.

It is possible that flow, like mentioned above, is restricted because of the filter, and Mobil I oil will almost always give lower oil pressure than regular oil.

 

[chevellejoe]

Thanks everyone for all your help.

 

[chevellejoe]

Like is said before this is a car that i am looking to purchase. The car is a good deal for the price, just want to look at all options to what could be causing this before i buy it and find that i am pulling the motor. The feeling i am getting, is the issue sounds minor which i have no problem fixing (Gauge, Oil filter, Oil, Oil Pump,ext). Of coarse you never truly know what you are going to get until you look into it. But i guess ill find out next week. Thanks again

 

[machinegun]

since this is a car you are going to purchase, it might be worthwile to find your closest Buick guru and if nothing else have them pull the fileter and cut it and possibly drop the oil pan to inspect. These are not hard and will cost a few dollars but if the owner and you agree to this it is a good way to help protect you both. I personally would not have a problem with this but sometimes others are less receptive. Somethign to look at though.