Thread: bad oil pressure

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i have a 77 gmc with a very modified engine after the last rebuild the oil pressure was fine today it seems a little lower than normal.
does anybody know what kind of oil pump i should use to raise the pressure over stock its the only thing still stock.

thank you

changed the oil a week ago, it a stock oil pump hocked to a mechanical oil pressure gage factory for 77, filter was changed with oil. way to much money in this to loose lees than 3 weeks old. both engine and tranny.

nice cobra by the way.

gam, how much of a drop have you noticed? Are you using the same viscosity oil, and the same brand filter? Are you comparing to the first start up after rebuild, or after the second oil charge after first flush? Are you comparing oil pressure at the same engine temp both times?

Oil pressure is not a "more is better" situation. A dramatic drop is a flag of a potential problem, but a higher pressure number is not an indicator of proper lubrication.

when the engin is cold the oil pressure is great when it is warm and ideling the gauge says abou 7-9. i just thought it should be higher

Hey Gam, My Mitchell system only goes back to 83 but 83 pickup with a 350 says normal oil preasure should be 35 to 40 lbs at 30 to 40 mile an hour (whatever the hell that means LOL) good rule of thumb
is 10 lbs for every 1000 rpm, of course if ya got 5w30 in it It'll be lower specially when it builds some heat......

so you think i should not worry runs great killer hp need to dino it to figure out what i got.it idles at 600-650 at 7-9psi oil pressure i just put a bottle of marvel mystery oil in it.

I would put a test guage on it, 7-9 psi would worry me. Cold to warm I generally like to see may be at most a 10 psi drop on a broke in motor 50psi cold 40 hot something like that. Sounds like a clearence issue what does the pump have on it miles wise or is it a new stock one? were the cam bearings replaced during the rebuild?

new stock replacement.the bearings were replaced so was the cam but the pump run off of the distributor drive gear. has allways had somewhat low pressure though.
you think i should put a high pressure pump in its place and if so what would you recomend.

You want a high volume oil pump, not a high pressure. Yes, your oil pressure is way to low according to what your saying, it should be at 40 psi for a new engine even if the gauge is wrong I would never rebuild an engine without putting in a new oil pump. You could have metal in the old oil pump that could wash through your bearings even if you clean it out some could get caught in one of the pockets or ports. Hope everything works out.

Vegas

P.S. Melling or TRW makes a really good oil pump.

THE PUMP IS NEW ITS A STOCK REPLACEMENT SORRY IF I SAID THAT WRONG I MUST HAVE.

I would first get an alternate gauge borrow one etc and see if there is a difference, if not I would worry there is a clearance issue somewhere crank rod cam etc possible oil gallery is cracked I have seen several things that cause this. Oil pumps are cheap probly 30 bucks can score you a hp hv melling unit a new screen and a pinned drive rod, note a lot of people would say to stick with a stocker because it take less hp to drive it essentially more horse power, I have had good luck with the stock replacement it should hold a good 40psi unless one of the aboves is a problem. just my 2 cents I have built a few chevy motors before and have owned several with teribble oil pressure and most of the time its crank and cam bearings that cause it and one that had a bunch of orange formagasket stuck in the pick up too, but mostly clearance once hot lets the oil just fly past it starving the rest of the motor.

Originally posted by gam41480
...after the last rebuild the oil pressure was fine today it seems a little lower than normal.

...new stock replacement. the bearings were replaced so was the cam

Did you check clearances on the bearings when you replaced them? Was the crank machined? If you've got a little too much clearance, you'll get low oil pressure at lower RPM's... just a thought.

Dan J

Gram,
I wasn't saying that you did't replace your oil pump I was just saying that I wouldn't rebuild an engine without replacing your oil pump. I have seen some people just clean out their oil pumps and put them on a new motor. I don't know if you misstated high pressure oil pump or you meant to say that because I used to think that a high performance oil pump was high pressure when thats not what you want at all, you want a high volume because too much pressure could cause other problems. Another thing you have to take into mind to is what type of bearings you are uing because, fully grooved bearings could cause a drop in oil pressure, especially if there is some type of clearance problem. Sorry for any misunderstandings hope everything works out for you and Happy New Year.

Vegas

bought a moroso mor-22110 fixed the problem thanks guysoil pressure is 30 psi at idle 60psi at about 6500 rpm