My 1970 455 GS Started running hot

Discussion in 'Street/strip 400/430/455' started by Stan Johnson, May 18, 2021.

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  1. Stan Johnson

    Stan Johnson 70 GS 455

    My car always ran about 195 deg. A few days ago it started running 225 deg. consistently. Not boiling anything out. I changed stat but that did not help. Radiator is clean and has great circulation. Clutch fan feels really stiff. I can't spin it a half turn. Should I replace it?
     
    Stan Johnson, May 18, 2021
    #1
    69GS430/TKX likes this.
  2. OHC JOE

    OHC JOE Mullet Mafia since 2020

    I'd change fan clutch
    Pops car was the same felt firm
    I replaced it and that was it.
     
    OHC JOE, May 18, 2021
    #2
    john.schaefer77 likes this.
  3. Stan Johnson

    Stan Johnson 70 GS 455

    Thanks Joe. Spinning fan as hard as I can I can't get a half of turn out of it. I have an Acdelco on order.
     
    Stan Johnson, May 18, 2021
    #3
    OHC JOE likes this.
  4. john.schaefer77

    john.schaefer77 Well-Known Member

    Hot idling or when driving at highway speeds?
     
    john.schaefer77, May 18, 2021
    #4
    bobc455 likes this.
  5. bobc455

    bobc455 Well-Known Member

    If this is happening while driving 30+ MPH, it has nothing to do with your fan clutch.
    - Is your temperature gauge accurate?
    - Any air in the system?
    - Anything blocking airflow (piece of debris etc.)?
    - Did you just start running your A/C?
    - Is your lower hose collapsing when you rev the engine?
    - What is your coolant-to-water ratio? Any additives (water wetter, RMI-25, etc.)?
    - Any other changes you made around the same time?
    - Where is your temperature probe located?
    - What is the rating of your thermostat?

    -Bob C.
     
    bobc455, May 18, 2021
    #5
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  6. OHC JOE

    OHC JOE Mullet Mafia since 2020

    Keep us posted Stan
    Hope it all works out
     
    OHC JOE, May 18, 2021
    #6
  7. Stan Johnson

    Stan Johnson 70 GS 455

    Bob,

    Below are replies to your questions.
    It runs a little cooler at hwy speeds. Maybe 220
    I gotta believe the temp gauge didn't change overnight.
    Doesn't appear to have air in the system as it's flowing fine.
    Nothing blocking the cooling system.
    The car does not have AC
    50/50 Coolant mix
    No changes made other than topping off the reservoir.
    New stat is 195. Old stat was 190
     
    Stan Johnson, May 18, 2021
    #7
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  8. john.schaefer77

    john.schaefer77 Well-Known Member

    Sounds like it is airflow. I think you're on the right track
     
    john.schaefer77, May 18, 2021
    #8
  9. Quick Buick

    Quick Buick Arlington Wa

    Never Ever Worked..... Stat is shot...
     
    Quick Buick, May 18, 2021
    #9
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  10. Stan Johnson

    Stan Johnson 70 GS 455

    I hope so. Clutch fan is supposed to arrive Thursday. I'll keep ya posted. Thanks for the help!
     
    Stan Johnson, May 18, 2021
    #10
  11. LARRY70GS

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

    The engine won't run cooler if the thermostat won't let it. If you choose a 195* stat, expect the engine to run at 200* or more. I prefer my engine to run at 180*, I use a 180* stat. If the radiator is a brass/copper 3 row, and it is old, it will be at least partially clogged. I don't care what you do to it, flush it with whatever, it will not do any good. You can't beat a 2 row aluminum radiator with big tubes.

    Check your ignition timing. A stuck mechanical advance and/or defective vacuum advance will make the engine run warm because of retarded ignition timing.

    You are not supposed to get more than 1/2 a turn out of the fan clutch. It is likely fine.
     
    LARRY70GS, May 18, 2021
    #11
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  12. Stan Johnson

    Stan Johnson 70 GS 455

    Timing is right on and electronic ignition. Also this issue suddenly happened. Something changed. Still starts and runs the same.
     
    Stan Johnson, May 18, 2021
    #12
  13. LARRY70GS

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

    I'm talking about checking the total timing. That entails checking the mechanical and vacuum advance, not just the initial timing. That has nothing to do with the electronic ignition. If the mechanical advance was sticking, or the vacuum advance canister stopped working, that would cause a sudden increase in coolant temperatures. Ignition timing at cruise RPM (2000-2500) should be approximately 40*.
     
    LARRY70GS, May 18, 2021
    #13
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  14. Stan Johnson

    Stan Johnson 70 GS 455

    Ok I'll check it but if that failed I would think it would idle poor and have no acceleration. Neither is an issue.
     
    Stan Johnson, May 18, 2021
    #14
  15. LARRY70GS

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

    If just the vacuum advance canister diaphragm failed, you wouldn't notice it in performance. Vacuum advance goes away under higher throttle openings, but in normal driving and cruise, it adds timing for better mileage and cooler running.
     
    LARRY70GS, May 18, 2021
    #15
  16. Stan Johnson

    Stan Johnson 70 GS 455

    Ok makes sense thanks
     
    Stan Johnson, May 18, 2021
    #16
  17. LARRY70GS

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

    Unhook the hose to the canister and apply vacuum to the hose with a vacuum pump, or hook it to manifold vacuum with the engine running at idle. You should be able to watch the timing increase and the engine should speed up. It isn't uncommon for the canister to stop working because the diaphragm develops a leak. Not the kind of thing you would notice. I check mine every tune up.
     
    LARRY70GS, May 18, 2021
    #17
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  18. Stan Johnson

    Stan Johnson 70 GS 455

    Larry,
    Thank you very much. I will check that tomorrow!
     
    Stan Johnson, May 18, 2021
    #18
  19. LARRY70GS

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

    My pleasure, let us know what you find.
     
    LARRY70GS, May 18, 2021
    #19
  20. Stan Johnson

    Stan Johnson 70 GS 455

    I do not see a vac canister on this car
     
    Stan Johnson, May 18, 2021
    #20
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