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Oil PSI loss/Oil cooling how-to

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by newyorkin, Jun 11, 2001.

  1. newyorkin

    newyorkin 1 ton status

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    Hey y'all, I'm having some concerns about my oil pressure on hot days...

    10w-40 in '88 Chevy 350/TBI: After about 20 minutes of driving, oil pressure gets to zero (yes 0; used 1 electric and 2 hydraulic guages) at complete stops while in gear. Revving will bring it back up, but even then it's low, going to about 25 psi at 1500 RPM in nuetral. When cold/first 15-20 minutes of driving, pressure is about 40-60psi, getting lower as it gets hotter. It also seems like the hotter the weather, the more RPM it takes to get any pressure back up.
    This isn't a pump thing, right?? I switched to synthetic yesterday hoping it was just a sign of oil change time/thermal breakdown, but still had the same problem in a test drive last night. I've also had this problem in 4 other GM engines I've owned and 1 Dodge, without ever blowing one; 3 2.8 Chevy's, 1 350 Chevy before this one, and a 318 Dodge. Wife's 2.8 Pontiac is running the same oil but 5w-30, in same weather, and the pressure never dips below 20 psi in that car, even when half empty.
    Is it possible the oil is thinning out that much, that it's flowing through the engine without pressure?? When I changed the oil, I did it right after a long drive, and it was literally like water coming out of the engine, but the perfect amount (not overfilled), and coolant was at correct level.
    There is no noise when the reading is zero, no lifter, bearing, rocker noise, etc. Coolant temp reads perfectly normal, regardless of weather temp.

    Also, anybody know how to put in an oil cooler if there's not one stock? I mean where to pick up an input/output on the block? Is there some kind of adapter I can pick up and screw on at the filter?

    Ratch
    **<A target="_blank" HREF=http://k5.8m.com>http://k5.8m.com</A> What more is there to life?**
     
  2. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    What is your mileage? I run 20w50 on high mileage vehicles.
    And I think the recommendations for synthetic is even higher viscosities.
    The stock oil cooler is a plate that goes between the filter and block - I would check the dealer price on that. Mine came with it and it is great! Adds an extra .5 quart also.
    Did you make any progress on the TBI. I am sorry I never was able to scan that article..... Will keep trying if you need it.


    Dave

    "Visualize Whirled Peas"
     
  3. POWERMAD

    POWERMAD 1/2 ton status

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    summit sells oil cooler kits.
    But it sounds as if there are internal problems.
    Does the engine have a lot of miles on it?
    The oil pump could be going out or the bearings may have to much wear.
    A general rule of thumb is 10 psi for every 1000 rpms.
    Myself I like to see the oil pressure around 45- 50 at idle.
    No oil pressue at idle is not good. My 73 does this and I have to put it in nuetral and rev it up at stop lights.
    Needless to say I don't drive it much. I need to tear it down and see what is going on.


    my truck's not dirty, it's earth tone paint
     
  4. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    Oh yeah - if the engine is in good shape it would be worth replacing the stock pump with a high pressure/volume pump.

    Dave

    "Visualize Whirled Peas"
     
  5. newyorkin

    newyorkin 1 ton status

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    Thanks for the quick replies everyone!
    Has your engine temp improved with the oil cooler? I just want to basically put in another tranny cooler, but run the engine oil through it. I'll look into the aftermarket one.
    Mileage isn't that high, about 110,000 miles on the truck, and I assume the motor.

    Yes, engine is in great shape. I really didn't want to, but I guess I'll have to swap the pump...
    It just seems like (and I was really hoping for), an oil problem, not pump, since it has great pressure when cold.
    Bummer...

    Dave, thanks for the offer in the article. Whenever you get a chance if you wouldn't mind scanning and mailing it, that'd be great. That project is temporarily on hold until some funding increases... Although my local junkyard has an eye out for me for the casting, and will call me if he gets one soon.

    Ratch
    **<A target="_blank" HREF=http://k5.8m.com>http://k5.8m.com</A> What more is there to life?**
     
  6. muddin4fun

    muddin4fun 3/4 ton status

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    Sounds like a rebuild to me. You might try putting some thicker oil in there to get the pressure up a little. I would think if it were your oil pump, you wouldn't have much change if any change in the oil pressure at any RPM.

    <font color=red>I'm a psychic amnesiac. I know in advance what I'm going to forget. </font color=red>
     
  7. 2Dogs

    2Dogs 1/2 ton status Premium Member

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    My Blazer had the cooler as a stock piece so cant tell how much difference it would make. The cooler block would be easy but the lines and cooler will take awhile so I think you should do that first AND then an oil pump since the engine is good.
    I have an oil temp gauge on the vette so I watch carefully the effects of temp - I lose about 20 psi when I get to operating temp (but that temp is VERY high), that engine has 30k on it.

    Dave

    "Visualize Whirled Peas"
     
  8. 89Blazin

    89Blazin 1/2 ton status

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    I suggest runnin straight 30 weight and see what happens to the pressure. I realize you are now runnin with liquid gold (synthetic), but you can save/reuse it afterwards. I would think that if the pressure was actually gettin that low, the ole lifters would be barkin at you...

    85 Burb and an 89 Blazer
    One just for fun, one simply for pleazer
     
  9. curtis151

    curtis151 Newbie

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    That same thing happened to me.On start up the oil pressure would be at 60psi.when I ran it for about 20 min the oil pressure would drop to about 17psi.I don't think its your oil pump when they break they stop working all together.The reason my oil pressure was so low is because at start up the oil is thicker making your oil pressure higher as it heats up it thins out It will drop about 15psi.Dropping to zero means worn bearing (main&rod).
    If you've figured out the problem and its diffrent than what i said I would like to know(I've been wrong before)
     

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