RallyBoy1

My oil pressure seems kind of low on a new rebuild. At hot idle on an 80 degree day with the water temp at 195 the pressure reads approximately 15-18 pounds. Upon acceleration, the gauge shoots up. I have a stock style oil pump. Using 10w30 oil and I also have a new sending unit.
My bearing clearances are as follows:

Main Bearings .0028 .0030 .0028 .0028 .0029


Rod Bearings .0022 .0023 .0023 .0025 .0023 .0027 .0024 .0025

Do I need to have the engine pulled back out?

JooneJune

that does seem low. Is your gauge working? (Tried using an external gauge?)

did u inspect your pump before you reassembled? That little plastic sleeve on the pump drive tends to break very easily.

My vote is in the oil pump department...

RallyBoy1

I did not assemble the engine. The gauge seems like it is working but I have not tried to use an external gauge.

97 6SPEED Z

No, don't "throw the baby out with the bathwater" just yet. Your main bearing clearences are indeed a little on the "loose" side .... but .... here's what I would do. Next time you change your oil put in a fresh fill of 20w-50, and ... if your oil pump is working okay, you should see your hot (at idle) oil pressure under the conditions you described above, move from 15-18 psi to the 20-23 psi range. This will confirm for you that your oil pump is working fine, and that your lower hot idle oil pressure is due to your "loose" bearing clearences. If your oil pressure stays about the same (i.e. 15-18 psi) with the heavier 20w-50 oil ...... you may have a problem with your oil pump .... or oiling system. Also, if your oil pressure goes up at the rate of approximately 10 psi for every 1,000 rpm above idle speed ...... your oil pump/oiling system is probably NOT your problem.

RallyBoy1

Well, the oil pressure does increase approximately 10 psi for every 1,000 rpm above idle speed. Man, this is the pits. I will try to use a different oil and see if that makes a difference. I have only put 200 miles on it so far. I am hoping that the factory gauge is crap. What are the chances of that happening?

camarobird92

I run 20w50 oil in mine because I set up my bearings a little on the loose side. I like the thicker oil.

RallyBoy1

Anyone else wanna chime in?

WS6T3RROR

Put a heavier spring in the bypass on the oil pump. Unfortunately you would have to pull the oil pan to do this. Your oil pressure would likely go from 20-40psi at hot idle with the same oil. I have done this on junkyard pull out lt1's that only show 20psi at idle before and the oil pressure goes up to 35 or 40 at idle and 65psi wide open.

I am not sure why your builder didnt use a half shell (of a 0.001 undersize bearing) on that rod bearing that is 0.0027 or try moving the bearing around to a different rod. Looks a little goofy to me leaving it big when a half shell woulda put it right in line with the others. Oh well, little late now.

On a side note, as long as there is ANY oil pressure at idle you will likely never see any ill effect from this and the bearings will look fine.

First things first though, check it out with a mechanical gauge.

MachinistOne

Your clearances are loose by a few tenths, like he said above that one rod should have been corrected with a mixed shell combo. Secondly it should have been a high pressure pump installed (M55A) - I agree with what has been said, run a good 20w-50 and see if that puts you in a happier range.

RallyBoy1

Thanks gentlemen, I will check with a mechanical gauge first then go from there. I did talk with the machine shop and asked them what oil pressure i should be at. He responded around 20 or so. It is just the hot idle pressure that has me concerned. When I drive the car the oil pressure at cruise, 1800 rpm, is 40 psi and continues to increase with the increase in rpm's.

87bandit

those numbers aren't out of spec, just a little on the lower side