Oil pressure problem!

[Hawssie]

I have a 1970 c10 with a sort of crate motor in it. The motor was one of those newer design 1 piece oil seal 330 hp crate motors GM dealerships used to sell a lot of years ago with the then new "VORTEC HEADS" on a carburetor motor. This crate motor had a warranty problem and was replaced with a new one, in which time the parts counter guy ended up with it and had it fixed by a machine shop that did work for the dealership. He was going to use it but ended up trading it to me. This all happened about 10 years ago. I had the motor sitting around for 9 years and last year I put it in my 1970. Well I set it up and the oil pressure was fine as I remember but I never really drove it. That was about 8 months ago. Now I am back working on my truck and I took it out today for a 10 mile drive and I noticed the oil pressure was going to about zero at times. I took it home and put a mechanical gauge on it to confirm. and it seems to be around 25 psi at start up while warm. If I rev it up it will build to about 45 psi tops but after I take my foot off the throttle the oil pressure starts to gradually drop and bottoms out at 5 psi and sometimes lower. I checked the oil plenty of flow getting to the heads.No drivetrain noise. I have never had symptoms like this. It also sometimes jumps around a bit at times. What sets the oil pressure? I know bearing clearance problems will lower it but could it be in the oil pump maybe? Is it time for it to come back apart?

[truckdude239]

Pump just moves oil the bears clesrances are what make your pressure sounds like pick up is either to far off botttom of pan or to far down in the pan and sucking the bottom pan up blocking glow

[Old Truck Man]

Relief valve in oil pump could be sticking or not seating properly?

[LSUMurse]

I am so not the one to go to with a problem like this, but I remember reading a thread on here a while ago and someone was having similar issues. It ended up being the oil filter. Probably not your issue, but something to keep in mind.

[Hawghauler]

I believe you'll find a spring inside the oil pump. This spring regulates the oils pressure. I would pull the pan. Check the pickup on the pump for debris. Check the pan for debris. If it is all clear, take the bottom plate off the pump while in the engine. You can put a beefier spring in if you think it's too low. I would open the bottom of the oil pump and look at the action while it's in the truck. Check for any kind of movement between the lobes on the pump. Tape covered flat blade screw driver should do it. Take the pump out. While you have the pump off, I'd find a way to reach up and try to move pump driver on the dizzy shaft, maybe a 1/4 drive socket on an extension. If not, check the action of the pump. Check for movement between the shaft and the shaft gear, any movement that allows any play. Or just replace the pump and move on.

[LockDoc]

-
Sounds like the screen might have dropped off of the oil pump pickup tube, or the whole tube came off of the pump or it has the wrong dip stick in it and it doesn't have enough oil in it... Just some guesses...

LockDoc

[cwilkie]

Try a different oil filter. Years back when my 396 was new I used a short FRAM filter. No oil pressure. My dad told me to change the filter so I picked up an AC Delco oil filter and my problem was forever resolved.

[Hawssie]

Well at the risk of looking like a fool I will tell you what I found out. I decided to remove the pan to take a look, so I put the truck on the lift and put a 5 gallon bucket under neath. It had maybe a quart of PS fluid in the bucket. I started draining it and it filled the bucket up 1/2 full maybe a little more! That means it had 10 qts of oil in a stock pan small block! It turns out I used a dip stick and a tube that were not matching. I had to use a latter model stick and tube due to the 1 piece block and the tube was about 1 1/2 inches too long. That plus the dip stick was rusted and hard to read and the oil was new so very colorless. Anyways I must have put the 5 plus qts originally and after sitting for 8 mos I must have checked it again and added more because it looked low. Then when I had the oil ps problem I thought maybe the dip stick was off so I added 2 more qts thinking maybe the dip stick was off the other way! After I drained it I decided to refill and change the filter and now when its 105 out with the engine at operating temp it still puts out 25 psi at idle so I think I am alright. Thanks NIck

[leftybass209]

No biggie. Everyone has a moment from time to time. Sounds like you're back to truckin' with no problems. Just remember 5qts is 5qts. If you filled it up and you had no leaks or smoke from the tailpipe, it didn't vanish!

[Hawssie]

Thanks! But does anyone know if the doubling of oil would be a direct cause of the strange oil pressure symptoms I had? I am just curious. I did change the filter too so I guess it could be that maybe. The one little thing I did leave out is that when I put in new oil, being that out of 30 engines I own in different vehicles/equipment only 2 or 3 are gas so I have a lot of 15w-40 around. And since I was planning on just testing to see what would happen with the pressure and really expected on having to remove the pan I figured it would be alright to use what I had instead of going to town. So 15W should be effecting the oil pressure as well.

[truckdude239]

Yes if the oil is over full the crank will hit the oil causeing caviate and foam up allowing the pume to sucks oil.