Scotty I have a rebuilt Chevy 350 engine that has over 100,000 miles on it. It’s in a 1975 GMC Vandura work van. When the engine is running at idol, the oil pressure gage goes way down, but when it’s driving it’s normal and I’m not low on oil on the dipstick. I have a minor oil leak (only looses half a quart every 5,000 miles). Should I be worried that I have a major engine problem? What could the problem be?
When the oil pressure drops on the gauge, does the engine clatter and make excess noise? If so, then there's an issue with the oil pump. The pump is engine driven and it may not be pumping enough volume at low RPM, but it's making up for it at higher RPMs. If there isn't anything like knocking, pinging, or otherwise metallic sounds coming from the engine and it sounds normal, your pressure sensor may be bad.
There is no noise whatsoever. Thought It could be a camshaft bearing starting to wear? Or the oil pump starting to burn out? Just an engine showing it’s age and wear I suppose.
My initial reaction to it was the oil pump. I'd keep an eye on it, or replace it for peace of mind. Here's a tidbit I just read on an '85 Ford. https://www.chicagotribune.com/news/ct-xpm-2001-01-15-0101150132-story.html
Check that out, apparently there is a tool, even on those old vehicles to check the engine oil pressure from the sending unit. I
half a quart every 5000 miles is not bad at all.
I have the same engine in my 93 k1500 and it somewhat happens to me too but I don't hear any noises and the dipstick has 0 shiny particulates on it I wonder if its just normal.
You said you had a minor oil leak. Where is it leaking from?
Not sure yet. Trying to figure out. Personally, I think it’s either the camshaft bearings wearing out or the oil pump. Just an old engine showing it’s wear I suppose.
I would go with the oil pump. The old 350 small blocks rarely had cam bearing problems.
Actually I’ve heard that the ORIGINAL camshafts on a lot of 350’s back in the 70’s we’re bad and a lot of them had to be replaced. But this is a rebuilt engine so I know that it isn’t original.
I do remember that in the 70s, the cams would round over because of the very strong hydraulic lifters but I never heard of bearing problems. That's why a lot of guys went to roller lifters and cams.