Installed mechanical oil pressure gauge, these readings good?

Discussion in 'Small Block Tech' started by 72skylarkconvt, Aug 24, 2019.

  1. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Hello all. If you have seen my other threads you know I had a pretty good over heat early this summer. I have no idea if oil pressure numbers could be affected by a pretty hot over heat.
    I have a 72 350 with 125k orig miles, motor known to be orig, no work done to it.
    I finally got a mechanical oil press gauge on it. Here are the numbers I got.
    Cold start up it in park running about 4o psi.
    Driving while not totally up to running temp about 40 mph, about 36 psi.
    Driving at running temp about 40 mph 32 psi.
    At a stop in gear it was about 20 psi, later after driving for about 20 minutes it would drop to 16-18 psi
    At running temp after driving for a bit going about 50 or 55 it would get to about 32-34 psi.
    Running at running temp, in park about 20 to 22 psi.
    I ask, are those good numbers for this old car with these miles?
     
    Houmark and breakinbuick11 like this.
  2. alec296

    alec296 i need another buick

    Yes. That’s pretty decent for oil pressure.
     
    Houmark likes this.
  3. Mark Demko

    Mark Demko Well-Known Member

    Yes those are AWESOME numbers:cool:
     
  4. MrSony

    MrSony Well-Known Member

    10psi per 1000rpm. numbers are good.
     
  5. StfSocal

    StfSocal Well-Known Member

    This right here is the key.

    I would say that MPH has little to do with it but rather RPM is what matters. You hot idle PSI is good, and like stated you should see 10PSI increase as the RPM increases. Keep that gauge on there and go enjoy it.
     
  6. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Well from the relies here it appears I have a healthy motor oil pressure wise for the age and miles. The motor is quiet and sounds "tight" if you will.
     
  7. TrunkMonkey

    TrunkMonkey Well-Known Member

    I consider from your post, your numbers to be "normal driving/cruising". All of those pressures are likely below 3000 RPM at speed (factoring a 3.42 or higher rear gearing), and 1100 (at the most) for idles.
    Very good numbers.
     
  8. MrSony

    MrSony Well-Known Member

    Do you have a tachometer? Id install one so you'd be able to accurately tell what rpm has what psi. Also, how hot is your definition of hot when it overheated? Mine got to 230 driving down the highway, went up to 280 after I shut it off. Coolant was boiling rather aggressively. It ended up blowing a headgasket between #3 and #5. Replaced the headgaskets and 1100 miles later and a new radiator, no signs of trouble yet.
     
  9. 72skylarkconvt

    72skylarkconvt Well-Known Member

    I do not know how hot it got, I could hear it boiling ( prob towards aggressive side) some in the radiator and the overflow tank. It only peeing a little fluid during that event. My dummy light never came on. Seems it was the old radiator in it that caused it to overheat. I have since replaced that, Tstat, all hoses, heater control valve (had a pin hole in it). Since then I have driven in 85 degree weather on the HWY and it stayed at 185, have driven around town for 20 or 25 min at a time and it stays at 180-190 maybe 195 sitting at a light. I am feeling I avoided any head gasket issues since I have good drives since that happened. No temps above 200 at any moment.
    When I drove it yesterday it was around my town, speeds of 25 to 50. Mildly pushing it to 50 and the car at running temp my PSI was about 32-34. At cold start up in part it was around 42 PSI. Once at what I felt was running temp at idle at a stop it dropped to about 18 psi, put in park that went to about 20-22.
    I would think after driving on HWY a few times and around town more, if I had a head gasket issue from the overheat I would have seen issues from it by now.
    When I have this in for the TC fix, is there a test the shop can run for any head gasket issues?
    I do not have a tach on it at the moment.
     
  10. TrunkMonkey

    TrunkMonkey Well-Known Member

    You can get a "block test" (checks coolant for combustion gasses) at most auto part stores.

    https://shop.advanceautoparts.com/p/lisle-combustion-leak-detector-75500/25961533-P


    Very important to have expansion room at the top of the radiator when you test, as engine RPM and the t-stat cycling can result in a surge of coolant and any coolant that gets into the test tube will contaminate the detection fluid and provide false readings.

    I do several tests, and good rinse between tests of the tube and rubber stoppers.

    If you do not have a vacuum source (engine vacuum line to manifold is normally enough) you can use a tube in your mouth to draw enough to get good readings.

    Positive will indicate combustion gasses getting into the coolant side, and can be from cracked head, block, blown head gasket or in some cases intake exhaust/coolant passage crack.
     
  11. MrSony

    MrSony Well-Known Member

    The absolute hottest oil will get under normal circumstances is after a 20ish minute highway drive. If you got at least 10psi after that at idle in gear, and at least 10psi per 1000rpm, and it raises instantly with rpm, youre golden.
     
  12. 72skylarkconvt

    72skylarkconvt Well-Known Member

    So in other words it can seem to be running well but I could have any of those issues that are bigger than my TC cover leak.
     
  13. alec296

    alec296 i need another buick

    I would suggest a new radiator cap also.
     
    Mark Demko likes this.
  14. 72skylarkconvt

    72skylarkconvt Well-Known Member

    New rad cap on it also.
    I wonder if I should do the test for combustion gases in the rad and do a compression test to see if I catch any signs of other problems from my overheat? What says the crowd??? I have prob put 50 miles on it since the over heat, have never seen signs of water on the dipstick (have not checked the bottom of cao that is in valve cover and no oil floating in rad or overflow tank or on bottom of rad cap, it is green (fluids) as can be.
    Am I overthinking my overheat and I just go ahead and fix the TC cover and related parts as needed once opened and looked at?
     
  15. MrSony

    MrSony Well-Known Member

    What temp did it get to when it overheated? Do you have a gauge? Died your dummy light work?
     
  16. 72skylarkconvt

    72skylarkconvt Well-Known Member

    I don't know temp when it over heated. It was boiling some in the radiator, I could hear it when I pulled over and shut it down. The dummy light never came on although it came on when you start the car then goes off. I did get a mech temp gauge on it before I replaced the eventual fix (radiator) and when I drove it once it got to 220 to 230 on the HWY and would have kept going but I shut it down till it was cool and got it home (less than a mile).
     
  17. MrSony

    MrSony Well-Known Member

    I wouldn't exactly call coolant boiling overheating, buts its close.
     
  18. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The dummy light doesn't come on until 246*:) A 50/50 mix of AF/Water under 15 psi will boil at 268*
     
  19. 72skylarkconvt

    72skylarkconvt Well-Known Member

    Well at the time when it over heated the light always came on at start up then would go out as it should. Seems then it never got past 246 or there about since the light never came on.
     
  20. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Correct, but if you heard it boiling in the radiator, it likely was. You either had a weaker coolant mix, and/or your cap wasn't applying enough pressure and it boiled at a lower temperature, maybe 245*:)
     

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