Upper rad hose being sucked closed when engine is warm, motor revs?

Discussion in 'Street/strip 400/430/455' started by Canadian GS 350, Jan 13, 2021.

  1. Canadian GS 350

    Canadian GS 350 Well-Known Member

    Guys, any ideas why this is happening when engine is running, warm. If you rev it when temp is 200, the upper hose starts to collapse. I have a new TA performance 180 t stat. New 5 blade water pump, running a/c pulleys....I put a spring in lower rad hose, it seems fine. Thanks, Brad
  2. john.schaefer77

    john.schaefer77 Well-Known Member

    Check radiator cap.
    1973gs and gsx455-4ever like this.
  3. gsx455-4ever

    gsx455-4ever Gold Level Contributor

    X 2
  4. Schurkey

    Schurkey Silver Level contributor

    Rad cap first, but the second thing is a plugged hose for the overflow. Third would be an aged/degraded upper hose. Fourth would be a suspect thermostat.

    Any problems with overheating?
    Last edited: Jan 14, 2021
    john.schaefer77 likes this.
  5. Canadian GS 350

    Canadian GS 350 Well-Known Member

    New acdelco rc27 being picked up Friday. Since installing a temp gauge, I’ve noticed temps in the 215 range at times. I have a new TA 180 t stat, 7 blade clutch fan and shroud. What I witnessed yesterday, upper hose sucked closed when I rev the engine when the t stat should be open (gauge at 200) is a first for me. Once the hose relaxes, you can see temp drop.
    I hope new rad cap is cure. If not, I’m buying a good quality upper hose next.
  6. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    If your coolant temperature is not within 10* of your thermostat, you have a deficiency in your cooling system.
    ranger and john.schaefer77 like this.
  7. 6769RIV

    6769RIV Platinum Level Contributor

    Any chance the thermostat might have gone in backwards (should be "bullet in the Buick") or maybe burping the cooling system wasn't quite complete during refill?
  8. BYoung

    BYoung Stage me

    If the problem with the hose collapsing began after you installed the t-stat then I would start with the t-stat.
  9. Canadian GS 350

    Canadian GS 350 Well-Known Member

    It’s a weird one for me.......I use a system called “air lift” when filling. The tool creates a vacuum of the system, refills itself by sucking the coolant into the system by the vacuum created.

    After I try the rad cap, if it solves issue....great.....if not, new rad hose, will check position of t stat when changing rad hose.

    Never seen an upper hose suck shut while engine is operating.
  10. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    The radiator cap maintains pressure in the system. If there was pressure in the system, the hose would not collapse.
  11. Schurkey

    Schurkey Silver Level contributor

    Edited my prior post to include a plugged overflow hose. The radiator hose can't "suck" shut without low pressure in the system, and the overflow hose has to flow in order for the vacuum-relief valve in the cap to relieve vacuum.

    How do you create vacuum? Engine is hot, coolant pressure gets relieved via the rad cap. Then engine RPM increases, air flow increases, and the temp drops a little. Lower temp...lower pressure.
    Last edited: Jan 16, 2021
  12. Canadian GS 350

    Canadian GS 350 Well-Known Member

    I just took the overflow hose off....perfectly clear. Heading down to GM to get the ACdelco RC27 cap......the other cap was a 13 lb “S” ....made in Mexico cap.....
  13. Canadian GS 350

    Canadian GS 350 Well-Known Member

    E7D857CD-AF04-43FC-9B8C-FC7B826CEAC6.jpeg 947C8002-E7B9-47B7-967F-35296535621A.jpeg 114CB935-6488-45A3-A6A7-3F8B8C139561.jpeg 7DC93C2F-CCF5-477B-942E-E6754A001755.jpeg Put the new acdelco rc27 cap on, a new hose from rad to overflow tank, drove it Friday afternoon.
    - could not duplicate collapsing upper rad hose....so that was good.
    - coolant temps for the most part stayed between 175-190 once warmed up (180 t stat)

    I may be watching the gauge too much.....it seems very responsive to fluctuations as the system cools the car. I have the transducer mounted in the intake where the vacuum tcs used to be.

    See pics of old cap versus new.

    For sure big improvement
  14. john.schaefer77

    john.schaefer77 Well-Known Member

    Great news. Glad it was an easy one.
    Clarkie likes this.

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