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Thread: One extreme to the next

  1. #1
    Join Date
    Jun 2015
    Location
    Lewiston, South Australia, Australia
    Posts
    31

    Default One extreme to the next

    I've been dealing with apparent high oil pressure and fitted a mechanical gauge to confirm.
    NO HIGH OIL PRESSURE original gauge telling lies
    Mech gauge shows 45 psi idle cold and 55 psi driving
    Warmed up and 2000 rpm running 45 psi but idle at about 4 - 5 psi
    Any light touch on the throttle and pressure comes back instantly
    When driving and I back off the gas the gauge steadily comes back until about 18 psi when it falls like you've shot it to 0 then comes back to 4 psi.

    Any ideas what I'm likely dealing with this time?
    Filter bypass valve?
    Oil cooler blockage?

    Truck done 370,000 kms
    Runs beautifully, no nasty noises, no oil usage, oil clean, burns clean and good fuel consumption rates
    1997 Sierra 2500 Std cab, 6.5ltrTD, pretty much stock.
    Remote PMD, #9 resistor, dual lift pumps, new GM8 turbo, manual waste gate,10lbs boost, 2.5" cross pipe, 3" dump chamber, no cat, 4" turbo back exhaust

  2. #2
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    The later 6.5 engines (96 and up) have oil squirters in the main bearing webs.

    These holes in the main line have little aluminum orifices in them to shoot a stream of oil at the bottom side of the piston crowns.

    After the oil temperature comes up the pressure drops off a lot at idle due to the 8 LEAKS in the oil system.

    I have never seen one drop off to zero and then creep back up.

    4-5 psi is a bit low even for a squirt block.
    The last squirt engine I built up would hold 15 psi at idle hot


    Depending on several factors (Miles on the engine and wear) the low pressure might be explained.

    One worry on these squirt blocks is MAIN WEB CRACKING

    I have seen center main webs (3) crack through the oil squirt holes and then the crack propagates up into the lower cylinder area.

    This sort of anomaly could explain the low pressure.

    The drop to zero makes me nervous.

    About the only way to really know whats going on is to pull the engine out and strip it down.

    Sadly to get a good look everything needs to come apart including getting the crank out and washing the block so a visual can be had......


    If the block shows no main web cracks and BE SURE ALL 8 SQUIRT NOZZLES ARE IN THE SQUIRT HOLES then a fresh set of bearings including the cam bearings and a new oil pump will be the ticket to getting the pressure up to where is needs to be...

    The squirt engines use a high volume pump.

    A standard (Early engines) pump will not deliver enough oil....


    Sorry I can't be more positive.

    Good luck
    Keep us in the loop
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  3. #3
    Join Date
    Apr 2001
    Location
    CA
    Posts
    13,573

    Default

    That pressure is too low if the gage is accurate.
    The bypass/relief valves are possible (and easy to replace), but they would be on the list of least likely. Assembly seal compounds can foul them, but that's about it. Other fouling indicates another failure, and they would be the least of your problems. Doesn't sound like it to me.
    The oil pump is possible, but they rarely ever fail or weaken. Most likely, if they are a problem, defective since new.
    Perhaps have a look at the oil you're using. What brand and grade? The 6.2/6.5 can be a bit picky, and sometimes it's only that simple. Most 30W will cause complaints of one type or another.
    1985 Blazer 6.2
    2001 GMC 2500HD D/A
    dmaxmaverick@thedieselpage.com

  4. #4
    Join Date
    Jan 2001
    Location
    New Hampshire - Live Free or Die
    Posts
    6,057

    Default

    My first guess would be that the oil pressure relief valve is sticking, or has some crud stuck in it, or both.
    The Constitution needs to be re-read, not re-written!

    If you can't handle Dr. Seuss, how will you handle real life?

    Current oil burners: MB GLK250 BlueTEC, John Deere X758
    New ride: MB GLS450 - most stately
    Gone but not forgotten: '87 F350 7.3, '93 C2500 6.5, '95 K2500 6.5, '06 K2500HD 6.6, '90 MB 350SDL, Kubota 7510

  5. #5
    Join Date
    Apr 2001
    Location
    Newberg Oregon
    Posts
    12,282

    Default

    I hate to be hanging crepe....but my worry is a cracked center main web....
    (1) 1995 Suburban 2500 4x4
    (1) 1997 Astro
    (1) 2005 Suburban (Papa Smurf)
    THIS IS BOW TIE COUNTRY

  6. #6
    Join Date
    Jun 2015
    Location
    Lewiston, South Australia, Australia
    Posts
    31

    Default

    Thanks guys
    I'll start with the easy stuff and do the bypass valve and fresh 15w40 oil. I did change to 10w30 when I thought I was dealing with high pressure.
    Grasping at straws I know but have to start somewhere.
    Do you need any special tool to change bypass valve?
    Last edited by Drillman; 05-11-2020 at 16:17.
    1997 Sierra 2500 Std cab, 6.5ltrTD, pretty much stock.
    Remote PMD, #9 resistor, dual lift pumps, new GM8 turbo, manual waste gate,10lbs boost, 2.5" cross pipe, 3" dump chamber, no cat, 4" turbo back exhaust

  7. #7
    Join Date
    Feb 2014
    Location
    NC
    Posts
    32

    Default

    What brand oil filter?
    1995 K3500 CCLB 6.5 turbo diesel

  8. #8
    Join Date
    Jun 2015
    Location
    Lewiston, South Australia, Australia
    Posts
    31

    Default

    Used a Ryco filter last change
    1997 Sierra 2500 Std cab, 6.5ltrTD, pretty much stock.
    Remote PMD, #9 resistor, dual lift pumps, new GM8 turbo, manual waste gate,10lbs boost, 2.5" cross pipe, 3" dump chamber, no cat, 4" turbo back exhaust

  9. #9
    Join Date
    Dec 2003
    Location
    Yukon Canada
    Posts
    1,612

    Default

    Do you still have your old filter?
    If you do cut the can open and have a look at the media inside.
    If not it may be worth the cost of a filter to cut the one you have on the engine now.
    It inside may show signs of the reason for low pressure,ie metal in the filter.
    90 Chev 3500 c/c 4x4,6.2na,400 auto,4:10 gears.DSG Timing gears,main girdle, isspro tach, pyro,boost,oil and trany temp.Dual Tstats, High volume peninsular pump,on shelf, Custom turbo and intercooler 85%complete. Change of plans for the dually, it's going to get a Cummins. Both trucks are Blue 90 4x4 crews

  10. #10
    Join Date
    Jan 2001
    Location
    Knoxville,Tennessee
    Posts
    2,639

    Default

    Or an oil sample sent in for analysis
    "The Constitution is not an instrument for the government to restrain the people, it is an instrument for the people to restrain the government."
    -Patrick Henry


    A5150nut
    2006 K3500 D/A
    94 6.5 4x4 5spd Sold

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