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80+ oil PSI in new SBC

13K views 37 replies 10 participants last post by  lg1969 
#1 ·
Fired up my rebuilt 388 chevy (350 bored .060 over and 3.75 crank) and it ran prefect but the oil pressure at 2500 was at 80 psi and would keep climbing the higher the rpms went. Got up to 4000 and she was close to 100lbs! we shut the motor down after this and had no leaks or other problems. Oil pump is in a package from summit which came with a 7 quart pan and a pickup. oil is straight 30w. no oil leaks or gaskets blowing out. just wondering if the relief spring isnt working or whats going on. bearing clearances are around .02-.03
 
#5 ·
Straight 30w oil is thicker when cold than multigrade motor oil (like 10 or 15w-30 or 40, like you'll presumably be using after it's broken in).

And the engine is spanking fresh. Likely once the cam's broken in and you are running the oil you'll normally be using, you'll see a reduction in the hot oil pressure.

If not, then I'd be looking into the pump bypass spring being too stiff or piston sticking shut. Also be sure the gauge is accurate.
 
#7 ·
Never checked oil pressure at idle because the engine was on break in so i tried not to let it idle. oil was never up to operating temp because we only ran it til water temp went to around 160 or so. Hoping that when we change to 10w-30 it will decrease some of the oil pressure.
 
#14 ·
I suppose one big thing to ask is what is the temperature around engine? If it's extremely cold, by that I mean freezing and lower, the oil will be very thick. It could be so thick that even with the bypass open the amount that can pass thorugh the bypass hole is not sufficient to lower pressure inside the engine. If this is in a very cold place I recommend dropping the oil from straight 30 to 5W20. Surprisingly most oils straight, multi, mineral, synthetic all tend to congregate in a fairly tight viscosity range at 200 degrees F, but at freezing and below the viscosity differences are very large. So frozen 30 weight is a lot stiffer than frozen 5W20. But and maybe surprising is that 30 weight and 10W40 follow a pretty similar curve so the heavier multi-weights don't really improve on the very cold viscosity situation over the straight 30.

The other possibility is that the bypass valve is hung up. This could be a spring problem or the valve is physically restricted from opening the bypass hole, this is usually caused by a burr left when the bypass hole was drilled that catches the valve shuttle.

Bogie
 
#15 ·
Temp was in a heated shop kept constantly at 55F. never inspected relief spring in oil pump just looked at the roll pin that was installed so that the spring couldnt be tampered with. screw on filter also is stock style that has bypass in it. should i pull the pan and look at the pump and inspect or continue with break in?
 
#17 ·
Unless you installed a high pressure pump from which you expected a 100 psi cold idle, I'd surely drop the pan and pull the pump. Quality being what it is these days pumps need to be disassembeld and inspected before use, it's become quite a problem.

When using the old (and trusted rule) of 10 PSI per thousand RPM there is little reason for an engine to operate with more than 70 PSI hot and that would be 7000 RPM which most engines can't reach, not to say yours isn't designed for that, I don't know.

I personally like more pressure at idle so work with a variable rate spring and oil viscosity. My Frankenmouse motor with 15-40 in it idles cold at 55 psi, that quickly rises to 70 where the relief opens when the RPMs climb. Hot it idles at 25, cruise RPMs of 2000 in overdrive nets about 55 psi this climbs to 70 at 3000 RPM where the relief opens.

Bogie
 
#18 ·
well i dont know what pressure is like at idle because since it is break-in i tried not to let it idle. took it too about 2500 rpm and pressure was about 80 lbs. only reason i blipped it too 4000 was to see if the bypass would kick on and if the pressure would keep rising. really thinking i should probably drop the pan and look at the pump. what should i look for when i pull it apart so i know if its the spring of whatever is wrong.
 
#19 ·
Finnish your cam break in at 2000 rpm drain that break in oil to get out the contaminants change the filter add some zddp and 10 30 oil restart and see what your oil pressure is If your engine has very close tollerances it might be a little high if you ordered a high volume high pressure pump but forgot to open the pump passage or chamfer the crank oil holes! If its an early block and your getting pressure in the rear move your sending unit to the front of your block and see what the reading is.

Jester
 
#20 ·
hello

I have a 355 that when cold running vr1 10w-30 she is 75psi and will climb higher if im hard on it, but I usually just keep it cool or drive normal for 10-15 minuts until she warms up a lil, prolly when the oil filter bypass kicks off, and pressure drops to 60 even when pushing the car hard, and never gets below 35 real hot at a stop light. I was worried at first but everyone respectable I talked to said those were all ideal numbers and Id be fine. Let her get warmed up and see. I think anything below 100 will be ok youll just no real soon if any gaskets are leaking because youll see blowby or whatnot creeping out. NO biggie tho.:thumbup: Good luck
 
#32 ·
Alrighty! got her all broke in and oil pressure was about 45-50 lbs at 2500 rpm when up to temp. 850 rpm idle oil psi was around 25 or so dont exactly remember. drained the oil and everything looks good so far! just need to cut open the filter and look at that. My first engine build woohoo!
 
#34 ·
Cut filter open and found some very very fine metallic particles. Thinking that's pretty normal since its break in and new bearings and rings need to seat. Or should I be worried about it? Just some very fine metal particles. No chunks or anything noticeable like that.
 
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