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Oil pressure, how low is too low?

Discussion in 'The Hokey Ass Message Board' started by 63comet, Aug 7, 2013.

  1. 63comet
    Joined: Jan 31, 2006
    Posts: 508

    63comet
    Member

    At what point do you decide that the engine is a time bomb? Not going down the road and your pressure drops, but average oil pressure. Old, worn out motor that has seen better days type of oil pressure.


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  2. trollst
    Joined: Jan 27, 2012
    Posts: 1,783

    trollst
    ALLIANCE MEMBER

    Drive her till she makes noise, then it's too low, meantime, switch to a heavier grade.
     
  3. 63comet
    Joined: Jan 31, 2006
    Posts: 508

    63comet
    Member

    What kind of noise and how loud does it have to be?

    There is always some new ticking clicking rattle that drives me nuts until I just decide its not going away and live with it.

    When I was working at Neil's we had a lady drive her MGB in for a tune up. Didn't seem to be hitting on all four.

    Upon opening the hood we figured out why. Number three said "Screw you guys! I'm gone!" and left through a hole in the block.

    I did my brakes and suspension this past spring. Next years plan is engine.


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  4. 29AVEE8
    Joined: Jun 28, 2008
    Posts: 1,384

    29AVEE8
    Member

    Rule of thumb, 10 PSI per 1000 RPM.
     

  5. mechanic58
    Joined: Mar 21, 2010
    Posts: 681

    mechanic58
    Member

    I remember one time when I was just a kid, working at a local shadetree repair shop - a guy drove up in a '74 model Trans Am with a 455 in it. I could hear it knocking as he was coming down the road before he even pulled into our parking lot. He pulled up and asked if he could get his oil changed - he had his own oil and filter. So I pulled it into the shop and he gets his oil out of the trunk and hands it to me - NINE pints of STP and ONE quart of 50w motor oil. LMFAO!!! He said "that'll keep the light off for a few days".

    I also had a 302 Ford one time that ran on very low oil pressure for a very long time. I nursed it along for about 6 months on 90w gear oil. The timing chain finally failed and I had to shutter it. When it took it out of the car (it was in a pinto) I had it hanging on a hoist with the ass end of it pointed down at an angle. Oil began to run out of the rear main in a stream. I was just planning to throw the entire engine away because I already had another motor to go in it - but when I saw the oil running out like that I just had to investigate it further. When I got it apart I discovered that the lower halves of all 5 mains were completely gone and the crank was riding in the caps. You could move the crank up and down probably 3/8". That was one wore out sob!
     
  6. AlbuqF-1
    Joined: Mar 2, 2006
    Posts: 910

    AlbuqF-1
    Member
    from NM

    I've had a couple of engines with low pressure that would become sensitive to drive/coast conditions. The oil pressure would be low on drive (under load) and if I eased off the gas just a little, the pressure would climb 10 psi. About 100 miles later I threw a rod in both of them. I assume that kind of behavior is due to the thrust bearing loading/unloading.
     
  7. BOBCRMAN
    Joined: Nov 10, 2005
    Posts: 846

    BOBCRMAN
    Member
    from Holly

    Had a beater 69 Buick with a 350 in it. Light would stay on till 20 mph and never had more than 12 psi. oil pressure max on a gauge. Lasted over a year and then only died because girlfriend hit a deer with the car..:eek:
     
  8. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    had a old 225 slant six that when it idled the light would flicker on and off , slapped a sensitive gauge we had in the plant on there and it had 3 pounds of pressure , and had a slight knock , when you revved it it had 15 psi of pressure , I drove it that way for 4 years and when I pulled the engine at 260K miles I gave it t a freind and he still has it , still clacking away in a homemade tractor , says he will rebuild it when it starts to really knock .
     
  9. 63comet
    Joined: Jan 31, 2006
    Posts: 508

    63comet
    Member

    Fwiw... Ford 250 I6

    It was worn out when I swapped ten years ago.

    Warmed up my oil pressure hangs out around 20 psi going down the road, drops to like 5 at idle.

    I've been running 10-30 still, but suppose I'll see how it likes it if I change my trunk stash to something heavier. She also burns at least a quart every hundred miles.


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  10. stimpy
    Joined: Apr 16, 2006
    Posts: 3,547

    stimpy

    IMo its about due 10 psi warm should be the min . o ra slight knocking noise
     
  11. Fighter-of-Wars
    Joined: Nov 3, 2008
    Posts: 294

    Fighter-of-Wars
    Member

    Im with the old run it till it makes noise sorta deal.

    A little ot but years ago we had an old CAT D13000 diesel engine. One of the old chug a lug chug a lug 700rpm rigs on a well pump. Well it didn't make good oil pressure so they ran half STP and half 40 wt in the engine and finally decided to call the catman to look at it. He shows up looks at a bolt on the engine, gives it a turn and says "That should give ya another 30 lbs of pressure" Turns out that old engine had an adjustable oil pressure valve on it. Engine finally chunked a rod at about 13000 hours
     
  12. Automotive oil pumps put out an amazingly high volume of fluid. Pull the pan and clean the pick up tube screen and see what you get.
     
  13. I'd say it depends.....

    Different motors react to low oil pressure differently. And how low is low? If the motor isn't making too many noises (particularly low frequency ones that generally mean bad main bearings) and has running pressure of about 15 lbs or more, it could run a very long time if you don't beat it. My personal experience is that Ford motors will tolerate very low pressure, Mopar is next best, and GM least of all. If the motor has suffered poor maintenance, sometime a new oil pump will breath new life into them.

    I had a buddy who ran a 312 with essentially no oil pressure (it would show about 10 lbs when first started, then drop to zero as soon as the temp gauge moved) for over six months before he blew it up street racing (the one and only time...). Sounded like a dryer full of ball bearings, but it kept going....
     
  14. tfeverfred
    Joined: Nov 11, 2006
    Posts: 15,793

    tfeverfred
    Member

    My old 305 SBC ran at 10psi @ idle and 30psi under load for a few years. Never made a knock, until it let go one day. My new 350 SBC runs at 25psi under load, 50 at idle. Cruising, about 10 for every 1,000 RPM. I could almost use my oil gauge as a speedometer.
     
  15. 63comet
    Joined: Jan 31, 2006
    Posts: 508

    63comet
    Member

    You know, I hadn't even thought about investigating that. Thanks!

    If only I can get to doing it before I blow up the engine!


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  16. 1971BB427
    Joined: Mar 6, 2010
    Posts: 5,870

    1971BB427
    Member
    from Oregon

    The 10 per 1000 works OK as a rule, but under 10 is too low, and often engines run more than 10 per 1000 at higher rpm's. My 350 in my Suburban runs 20 at idle warm, and 50 cruising. My 327 in my Austin runs a steady 50-60 lbs. idling or cruising down the highway. The 454 in my Falcon never gets below 55 lbs. idling, and it gets up around 80 cold at over 2500 rpm's, so it exceeds the 10-1000 ratio.
     

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