SBC Oil Pressure Problem

[bob w]

I've got a recently rebuilt (about 1000 miles on it) 350 Chevy engine that has erratic oil pressure. It will go to 40psi when starting and then drift to 20psi even before warming up. Once warm it fluctuates during normal driving and will dip to 5 to 10psi when mildly on the brakes, accelerating or cornering. It doesn't knock. It is full of oil. Has anyone experienced oil pressure problems like this? What was the cause? This engine is in Big Dodge and it is very hard to drop the oil pan because the dummy that built the car (me) put a crossmember very close to the pan. That's why I'm looking for ideas before tearing into it. Thanks.
Bob

 

[Gastrick]

Mechanical or electric gauge? I would try a different gauge before tearing too much apart.

 

[24dodge]

If it`s not the gauge i`d look at the oil pump pickup next.

 

[Unkl Ian]

Pick up,oil pump,by pass spring,etc.

Most likely is the pick up might be loose,or cracked.
Also check the clearance between the pick up and the bottom of the pan.

I've heard of some strange problems directly related to Fram filters.

 

[24dodge]

I was thinking it may have even fallen off , normal pressure at start up , then as the oil level begins to drop the pump starts to cavitate.

 

[Dobber]

I would not be suprised if it is the pump, I did a rebuild on a 350 that was 60 over last year, and the pump that we got from O'rielly's went bad within the first week. Changed it out and the pressure was fine.

 

[24dodge]

if you know someone with a borescope , you could put it thru the oil drain hole and have a look around , gunsmiths , machinists and proctologists should all have one

 

[Unkl Ian]

Some of the "new" pumps are junk.

They cheaped out every step along the way on the design,to increase profits.

 

[bob w]

Tried 2 oil pressure gauges. One didn't work at all. A bad swap meet buy. The other acted the same as the original gauge. So, I shortened the drag link. That didn't help the oil pressure problem but it did reposition the pitman arm. Tomorrow I'll put a new oil filter on it and check the bypass valve on the block. After that doesn't work, it looks like I'll have to "go in". Like Unkl Ian pointed out, there are bad pumps out there. I kind of remember a story about the castings cracking, but I couldn't find the thread over on that other site.

 

[donsrods]

I had a GTO that did exactly that......coming to a stop or cornering the oil pressure dropped. Turned out the pickup fell off into the pan, like 24 Dodge said, and the oil was washing away from the little hole it was now going into.

Is your pump new? I would put a good Melling or similar stock oil pump on it and braze the pickup to the pump in a spot or two. It is something in the pump system I'm pretty sure.........bad bearing behave differently.

I wouldn't use a proctologist probe..........you never know where those things have been.

Don

 

[gasser55]

If it's a recent rebuild and the builder used moly assembly lube you may have a cloged oil filter.If not your oil pickup tube may have fell off the oil pump.Make sure to put a tack weld on the tube were it meets the pump.

 

[R Pope]

Put an extra quart or two of oil in it. If it holds pressure then, it's probably the pickup loose or fallen off.

 

[bob w]

RP,
I'm gonna try that. Thanks for the idea.
Bob

 

[ratty46pickup]

I`m gonna have to go with the crowd on this one. Had this problem on two engines. On both, the pickup had fallen off. If this is the case, weld that sucker!!!