Very strange Coolant problem. Possible head gasket? Help...

Discussion in 'Engine Topic' started by corellianvette, Sep 6, 2011.

  1. corellianvette

    corellianvette New Member

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    Hello! I've spent the weekend check out my new z28 and I have a question I could use some advice.

    http://www.nastyz28.com/forum/showthread.php?t=222864

    It's a 1979 Z28 w/ 350 Auto trans and HD radiator. Dual exhaust but otherwise stock appearing. I just got the car so I don't know a lot about it.

    One thing that's a bit troubling is something going on with the cooling system that I've never seen before.

    First, the car does not appear to overheat. In fact, underhood temps are pretty moderate even on the cool side. Checked with the car running and the thermostat housing only got up to about 190. I drove the car about 80 miles when I picked it up and was surprised how cool it was underhood. The gauge does not work properly, although the sending unit has Teflon on it so that may be affecting grounding/reading.

    So here’s the problem – when the car gets to operating temperature, the level of coolant in the radiator rises and falls pretty dramatically. It will suck down maybe 4 inches, then suddenly go back up and puke some out (just a little bit). Then go back down, and suddenly go back up and puke some more. I don’t see any “bubbling” which would indicate a head gasket, and the exhaust smells normal with no smoke. I tried “burping” the system twice, and it almost doesn’t matter what I do - coolant will fall, rise, puke, fall, rise puke. Pretty regularly. When I rev the throttle, the coolant will stay down. But back at idle, it will do the same thing.

    Also, the system does not pressurize. I did a pressure test on the system and it appeared to be OK (in that at 16lbs, it would drop, but very slowly). I tested the cap and it was bad (new cap on the way). I put a known good cap on the car but have not had a chance to see if that fixed the pressurizing problem.

    When I shut the car off hot, I can hear/feel gurgling from the thermostat and upper radiator hose.

    Has anyone seen this before? I’m hoping the bad cap is the problem, but the surging tank at idle is unusual to me.

    Thanks!
     
  2. Pfrederiksen

    Pfrederiksen Veteran Member

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    I would suspect you've already fixed it with a new cap.

    P
     
  3. kenny77

    kenny77 Veteran Member Lifetime Gold Member

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    Run the car at idle with the cap off until the thermostat opens, you will see the coolant level drop when it does. Now, fill coolant to the top and put a new cap back on.

    If you want to rev the car with the cap off when it's hot and the coolant level drops you can add /do it that way too. Add coolant when it drops then put the new cap back on. Your problem seems to be that the system is a bit low on coolant.....no biggie.
     
  4. corellianvette

    corellianvette New Member

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    I have watched the coolant drop when the thermostat opens. That's when the surging starts - which I thought was strange. I'm not sure the coolant is low, because the coolant level raises every few seconds....

    Let's hope it's just the cap...
     
  5. Skaal-tel 79

    Skaal-tel 79 Veteran Member Gold Member

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    You would know VERY quickly if it was a head gasket. I had the chance to drive a vehicle with a blown gasket and it was obvious within about 30 seconds.

    Between the river of coolant trailing behind the vehicle (out of the overflow) and the burbling sounds from under the hood, diagnosis was definitely not a lengthy procedure.
     
  6. K5JMP

    K5JMP Veteran Member Lifetime Gold Member

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    it could be a flaky thermostat..
    if you are really worried about the temp gauge, put a mechanical one in it even if only temporarily
     
  7. Damon23

    Damon23 Veteran Member

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    I have to concur with Kenny77 on this one. Gurgling = Low coolant level. I'd fill it up and while running and then leave the cap off for a while to make sure you have no air bubbles.
     
  8. corellianvette

    corellianvette New Member

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    That's the process I've been going through. What's wierd is that the level rises up and pukes out a little, then goes back down. If I fill it when the coolant goes down, it pukes a bunch back up. Then it goes down, comes back up, repeat....
     
  9. K5JMP

    K5JMP Veteran Member Lifetime Gold Member

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    which is why I mentioned a "fluttering" thermostat...:innocent:
     
  10. Skaal-tel 79

    Skaal-tel 79 Veteran Member Gold Member

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