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oil pressure drops

Discussion in 'Chevy Trucks' started by 350305, May 25, 2002.

  1. 350305

    350305 Junior Member
    Messages: 3

    I have a 1985 gmc W/ a 1971 camaro 350, 400 trans.
    What would cause it to have no oil pressure at idle and about 30psi at speed. When Istart it up, it goes to 60psi then drops as it warms up. The engine never gets hot. Changed gauge and oil press. sensor. No visible oil leaks.
  2. Chuck Smith

    Chuck Smith 2000 Club Member
    from NJ
    Messages: 2,317

    Worn connecting rod bearings. It won't be long before the motor develops a rod knock. Do an oil change, I bet the oil has a metallic look to it....

  3. scalawag

    scalawag Junior Member
    from 39740
    Messages: 7

    oil pressure 2

    hi fellas, like the other oil pressure discussion below, mine is exactly like his but i have 150psi compression and i believe the motor was a short block. so the builder may have put in an old oil pump. i cant hear any timing chain slap, a sure sign of alot of miles it runs like a sewing machine. my question is what is normal oil pressure at idle and after warmup. i was told 10 psi for every 1000 rpm. if thats the case the it would be just below 10 psi at idle. shouldnt it?
  4. DarinRay

    DarinRay Junior Member
    Messages: 20

    Well bump to the top.

    I wanted to throw this in---put a real oil pressure gauge (no electric) because I am having this voltage trouble with my 91 GMC just at the gauges so my volt gauge reads 14 v and then will drop down to 12.5 this causes all my gauges to read lower. When I come to a stop at idle the oil gauge falls off and my check gauges like comes on,,,give it some rpm and back to norm. I haven't found exactly what is up here but wanted to share. Any suggestions on my voltage?

  5. MTCK

    MTCK Senior Member
    Messages: 346

    Darin - Does your engine temp drop also? I'll bet not. 12.5 volts is normal for a truck at idle. Your alternator will bump it up to 14.4 volts when you're cruising, but isn't spinning enough to produce this much voltage at idle, a lot of times. Try turning off all your accessories, fan, lights, ect. and it will creep up a bit from 12.5. The reason the oil pressure gauge drops and goes up with the volt meter, is that you have lower oil pressure at idle, and it builds with RPM, and it just happens to coincide with the increase in voltage. I could be totally wrong, but that's my guess. Both my 83 and 91 do exactly that. 2000 doesn't fluctuate much, but it's still really new. Hope that helps a little.

  6. DarinRay

    DarinRay Junior Member
    Messages: 20

    Actually Marcus the voltage drop doesn't happen all the time but when it does I can be driving down the road at 55 mph and all my gauges start reading lower- water temp too. Come to think of it my interior lights will fade too and then brighten up again while driving. Thats why I don't have my gauge lights on - all the way dim for awhile now and just hope I'm not speeding. lol. As far as the voltage reading at idle and engine speed being lower I check my voltage with a volt meter at idle not going down the road at 55mph :) :eek: and with nothing on it reads over 14.2 and up. I have a dual battery system for my dump and plow and am wondering if there is some sort of sharing problem or something or a bad wire but haven't figured it out.:realmad: Hopefully we can find out here. Thanks

  7. joecampy

    joecampy Junior Member
    Messages: 2

    Check the connection at the starter termial. they feed the fuse panel inside from the main lug on the starter.

    had the same problem on my 86 sub.
  8. Mick

    Mick PlowSite.com Veteran
    from Maine
    Messages: 5,546

    Concerning oil pressure drop - I've got a '96 Chevy 3500 with a 6.5 TD. Normal pressure is 40, but it drops to 30 for awhile after hard acceleration, then back to 40 after about half a minute. It seems to stay at 40 any other time, including carrying a 9' plow and loaded 2 yd sander. Should I be overly concerned at this point?
  9. Pelican

    Pelican 2000 Club Member
    Messages: 2,075

    Mick, this may sound silly, but is your oil level correct? The conditions you describe are symptoms of a low oil level.

    Your oil pressure should rise with RPM, regardless of engine load. You will see higher pressures at start up until the oil warms up and thins out. Normal pressures in a good engine are 20 to 30 psi at idle and 30 to 45 psi at speed.
  10. Mick

    Mick PlowSite.com Veteran
    from Maine
    Messages: 5,546

    Thanks, Pelican. No, it doesn't really sound silly. That's the first thing I thought of. The "30 to 45" is where it is, I guess I'm just paranoid about any drop below 40 which is the middle mark. It does fluctuate above the 40 mark too. I've only owned gassers before, this is my first diesel so maybe I'm just "looking for something to go wrong".

    I had the dealer who sold it to me last summer check it out thouroghly (whole front end, drive train and rear axles) at the start of last winter, then again last week when I got the State inspection. They said I might need a new pitman arm before the inspection next year, so had that done. Otherwise, they're assuring me that there is nothing wrong with the truck.
  11. plowking35

    plowking35 2000 Club Member
    from SE CT
    Messages: 2,923

    At start up my truck has at idle 45 psi, when warm around 25 psi, after running real hard( like when towing) at idle it will be around 20 psi. But as soon as the rpms come up, pressure is back up above 40psi, and never drops when at running rpms.
  12. Jake00

    Jake00 Junior Member
    from Maine
    Messages: 19

    I just had to have my 94 350ci engine replaced with an AC-Delco long block. The old engine would have an idle oil pressure of 0, and at normal cruising speed would have maybe 15 or 20 pounds. She then developed the lower-end knock. Fortunately it was still under warranty, and the dealership paid for the replacement. The rebuilt engine has a low of about 20 psi. The Chevy dealership told me that Chevy says that 7 psi is normal, anything more is gravy ... and to not worry about it. Of course you have to keep up with oil changes, and make sure the level stays up in between.

  13. Knightcrawler

    Knightcrawler Junior Member
    from ohio
    Messages: 28

    your 94 was still under warranty, i thought it was 3/36000
  14. Jake00

    Jake00 Junior Member
    from Maine
    Messages: 19

    No ... the dealer I bought it from (used) knew the engine was bad, and he bought the 6 month/6000 mile warranty when I bought the truck ... and the engine was replaced under that warranty. It helps to know someone!