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Oil Pressure..

Discussion in 'The Garage' started by 78Suburban, Oct 20, 2005.

  1. 78Suburban

    78Suburban 1/2 ton status

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    Well, I had a chance to drive my truck around today, and once it warmed up, the oil psi at idle was a 5. and full throttle, it didn't go much higher than 30. This is a bad thing I assume. :o

    Gas wouldn't be detectable on the dip stick would it? I'm thinking maybe the old fuel pump actually had bled some into the crankcase... I just changed my fuel pump, but haven't changed my oil yet... but I'm not sure that its gas in the oil causeing the problem, because the oil doesn't really look abnormally high on the dipstick.. maybe a little high.. :confused:


    On a happier note, I flexed the burb out today at the maximum of what stock suspension will do... pics to come later tonight.. :D
     
  2. pauly383

    pauly383 Daddy383 Staff Member Moderator

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    Try putting a mechanical gauge on it , and see what it says , if you have any handy . The gauge could just be old . Had that happen before , where the gauge ( well the resistor behind gauge ) was bad and read low . Or the actual sender could be bad . Otherwise it could just be an old motor .
     
  3. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Good suggestion on the guage. Sending units are cheap if you don't have a mechanical handy, or just buy a mechanical for the tool kit.

    I had a truck with roughly 100k miles that idled well below 10 psi for another 50k until I got rid of it. I had 292 in a 68 GMC that barely registered at idle, maybe 5 psi, for about 5 years working as a car hauler.

    But that's not to say it won't fall on it's face tonight. It can also be symptomatic of washed out main or cam bearings, which means your getting no flow to anything down line as the oil all goes out the path of least resistance.

    I would replace the oil and filter before anything else. If it's still way low, check for oil flow at the rockers. If you're getting oil up the push rods on both sides, it should be fine for reasonable duty for some time, but you never know. It's definitely not something I would go across the country in like that…
     
  4. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    think he is running mechanical and new gauge fellas iirc...

    dude, change that oil asap..

    gassy oil = bad things
     
  5. 78Suburban

    78Suburban 1/2 ton status

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    I am running brand new mechanical gauges... I've got my finger crossed that the old fuel pump was sptting gas into the oil (man thats not something to be hoping for).. but if thats the case, then I may have it fixed.... I'll change the oil and see if its gassy after a few miles.. if it is, where should I go from there?
     
  6. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    that sounds almost exactly like my buddies truck, we pulled the motor out and pulled the pan and the pickup was laying in the bottom of the pan. i pulled the main and rod caps to check the bearings, and they were toast, took the crank with it. he drove it alot after we noticed it and im almost positive thats why he did so much damage. so fix it before you kill your bearings.
     
  7. 78Suburban

    78Suburban 1/2 ton status

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    Well, that was encouraging :eek1: ... So exactly how do I fix it? I'm not exactly a master mechanic :(
     
  8. big83chevy4x4

    big83chevy4x4 3/4 ton status

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    we are replaceing the crank, bearings, oil pump and pickup, this time welding the pickup to the pump. cost about $250 with a gasket set.
     
  9. 78Suburban

    78Suburban 1/2 ton status

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    I'm starting to think this motor is a waste to throw money into.. I bet I could find something with oodles more power for less than it would cost me to rebuild or make this motor good... Perhaps I should go on a hunt for a BBC... hmm........ I dunno, I feel like anything I do with this motor is simply fumbling in the dark, I might fix a problem, then again I might not... I just had a thought:

    Would an obserdly low idle speed cause low oil pressure?
     
  10. jhellwig

    jhellwig 1/2 ton status

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  11. 78Suburban

    78Suburban 1/2 ton status

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    idle speed

    maybe its just my idle speed causing the low pressure??? I'm pretty sure I have a vaccume leak and/or carb issues.... So if I address these, is it possible that my oil pressure will be fixed too?

    How much should the oil pressure be under hard throttle... it was getting into the high 30s, maybe 40.....

    :bow:
     
  12. Beast388

    Beast388 1/2 ton status

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    James.......as a general rule of thumb, you need 10psi for every 1000rpm when warmed up. Just as an FYI, I have 25psi at 800rpm idle and 65psi everywhere above 2000 rpm.

    I would definately change the oil and see if those readings improve. :eek1:
     
  13. 78Suburban

    78Suburban 1/2 ton status

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    wow thats discouraging.. will change asap, but I doubt if it will change my results.. :mad:
     
  14. mtn. burb

    mtn. burb 1/2 ton status

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    It takes 5 lbs. pressure to make a chevy motor live.

    After you change the oil, if it's still low at idle after warm, probably main bearings, like they said.

    You can band aid it with Lucas oil stabilizer, 50 wt, it will last ...who knows...months or years. Then just get a new motor. Unless you want to pull the pan now, and measure the bearings. You can have them fixed. Not easy though in the truck.
     
  15. diesel4me

    diesel4me 1 ton status Premium Member

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    listen to the bearings...shhhhh!...

    If you hear a woodpecker type noise when you start it in the morning after sitting overnight,then it quiets down,that's a sure sign of loose bearings.(tappets can do the same thing,but sound more "tinny" than a bearing knock).--but I had more than one Chevy,and a Buick too,that did that for many years,they had similar pressure readings as yours....never had any engine failures..

    As long as you don't rev the snot out of it,(especially on a cold start!)-and use thicker oil or additives like Lucas as suggested,I doubt it will pop on you for a long time (don't go TOO thick in the winter if its cold where you are,that will make it worse,not better!)--many engines have low oil pressure period,especially at idle..5-10 lbs is not uncommon on a high mileage motor at idle in drive,,and many never go over 30 psi even at highway speeds... it could even just be the oil passage to the sending unit or gauge is partly clogged with sludge,and isn't getting full pressure!. :thinking:

    Having 30 psi at idle and 45-60 psi is under ideal conditions on a tight new motor..if its 10-15 lbs lower or more,its not good,but it does not nessasarily mean impending disaster either.. :crazy:

    It might help to put a new oil pump on,maybe the pump is worn some,or the pressure relief valve in it is leaking..its not expensive,a stock pump for my 305 was 12.99 at Autozone..it won't help much if the bearings are worn,but more pressure won't hurt either..Personally,if it doesn't knock upon cold startup,I'd just drive it and not worry about it,and keep the right weight oil and Lucas in it and enjoy.. :crazy:
     
  16. 78Suburban

    78Suburban 1/2 ton status

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    so the 10w40 in it now needs to go huh? or can I use that type with an additive?
    How hard is it to replace an oil pump, could a mentally retarded noob do it? :p:
    thanks :bow:
     
  17. 4xcrazy

    4xcrazy 3/4 ton status

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    Yeah, thats what i kinda told him in the instant messenger thingy, i get that knocking every morning as well, with 240k on the motor, but i still have 30-45psi of pressure,,,all the time, more when driving down the road.

    running 20/50 oil,,all the time too.
     
  18. 78Suburban

    78Suburban 1/2 ton status

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    I went and looked. I have 3 new quarts of 10w30... So I'm gonna pick up 2 more quarts and a filter, and maybe some lucas additive. then drive it till it dies I suppose :(
     

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