oil pressure problem
 

I have a 434 sbc. with a motown block. i ran this car last year and when i let off at the end of the track my oil pressure would drop to 10lbs. so i put a new pump in this year with a copper gasket and it wouldnt hardly carry any pressure at all when it warmed up. so i put another new pump in and removed the gasket. same problem still. i was using a bolt on pump screen, so i removed this pump and brazed the screen. i dont think its sealed 100% but its prob pretty close. so today i take it out and it will carry 60lbs of pressure for a good while, if i get on it or cont. quick reving it it will drop down to almost 0 then climb back up to 20lbs and may hit 40 but if i rev on it it drops down as soon as i let off the throttle. im stumped. i run 20/w50 lucas oil with a wix racing filter. and yes ive tried a different gauge. any help will be greatly appreciated

Re: oil pressure problem
 

A couple of things come to mind after reading your post.
1. Have you tried a different oil filter. I know it sounds crazy but there are people who let a car sit all winter without changing the oil and filter. If the filter was collapsed and you never changed it just pumps well you get the idea
2. Did you remove the bypass spring before you brazed the pickup on? If it gets too much heat while brazing the inlet on it will get weak and can cause low oil pressure
3. Define pretty close. If there is a leak couldnt it pull air instead of oil? I could be wrong but I would think it would be easier to pull air through a gap than 20W50 through the pick up.
4. How old is the engine? could it have been built with loose bearing clearances and now that its got some wear on it its way too loose. Sounds kind of like when the oil is cold its ok but when the oil gets hot and thins out a bit its loosing oil pressure couldnt that be a sign of too much clearnace somewhere.
I am no engine builder by any means but thought I would throw it on here. I am sure if I am a idiot someone will tell you in a minute. LOL

Re: oil pressure problem
 

the engine has prob 75 passes on it. it is a new filter just put it on at the initial start up this year. no the bypass spring was still in it when we brazed it. it is the same problem as before the brazing though. i ordered a new pump from competition products with a bolt on pick up i guess i will try this to. im sure it would suck air easier than pulling the oil. when we brazed it we sprayed some soapy water and shot air into the pump to see how well it was sealed and it only had a couple of small leaks. but im for sure not ruling that out. im honestly stumped.

Re: oil pressure problem
 

Have you pulled some caps and looked at the rods and mains to see how they look and check some clearances? Another thing that comes to mind is this scenario.

Something was not right from the get go (IE not enoughf oil in the pan, pan that could not controll the oil ect) So when you crossed the finish line the pan was already low on oil or the pan could not controll it. You hit the brakes to slow down and whats in the pan goes forward away from the pickup uncovering it and oil pressure went low and hurt one or more bearings.

Re: oil pressure problem
 

I have had exactly what Rob is desribing. It hurt 1 rod bearing and was very low on pressure once warm at a idle. Never made any noise just lost oil pressure and this on a car with exhaust so I would have heard it knocking. When I dropped the pan the bearings all looked fine but one had lost it's tension in the cap, I almost reused it it looked that good. I put new bearings in with the old pump and it was back to idling hot at 40psi in gear again just new and went all last season like that.

Re: oil pressure problem
 

X2

Yeah, I'd be pulling some caps and checking bearings and crank. I had a Z28 that did that very same thing about 3 months after a rebuild with a new crank. I pulled the motor out and apparently the crank had not been tuftrided. It looked like it had 200,000 miles on it. GM warrantied the crank and I was back in business.

Re: oil pressure problem
 

i checked the bearings over the winter, just visually when i put the first new pump in. they all still looked brand new. i didnt get this motor in my car until late in the season and it still looked great.

Re: oil pressure problem
 

You might want to check the cam bearings. Have seen the same problem after it warms up goes low on pressure. Phil

Re: oil pressure problem
 

cut the old filter open and see whats in it. See If there is bearing material in it. If there is pull it apart and start looking for where it came from. If a cam bearing was coming apart there would be some in the filter.

Re: oil pressure problem
 

Since you're pulling the pan again anyways I would plastigauge all the bearings. High (good) pressure while cold falling off to little pressure warm is a sure sign of excess bearing clearance.