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6.2 Radiator

Discussion in 'The Garage' started by 78GMC1/2TON4x4, Feb 19, 2004.

  1. 78GMC1/2TON4x4

    78GMC1/2TON4x4 1/2 ton status

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    This coolant problem is really getting on my nerves. First i replaced my water pump on my 6.2. Then the thermostat and lower radiator hose. Everything seemed to run fine for about 1 day. Now the gauge like before will stay at 100 deg and when it starts to get hot it pops over 240 for atleast 60 seconds. And now from somewhere its leaking coolant from the radiator from a place i cant see....I guess im asking what the problem is with the leaking coolant because ive even added stop leak?!?!?! And is the thermostat bad? /forums/images/graemlins/truck.gif
     
  2. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I am having the same problem with my 406's cooling system, just worse, but only when my heater core is hooked up to my heater hoses. It will idle fine and stay at the temp it's sopposed to be at but when I rev it up it will jump up to 230-260 degrees then come back down but it will go back up again over and over. I think what our problem is is that somehow the system is wanting to stop flowing unitl it releases pressure somehow and allows the pump to pull more water in to the block. /forums/images/graemlins/thinking.gif Why it's doing this I don't know. /forums/images/graemlins/dunno.gif
     
  3. 78GMC1/2TON4x4

    78GMC1/2TON4x4 1/2 ton status

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    ya if you let mine idle for even two minutes the gauge is out of control and over 240....i dont know whats going on...the heater starts to blow out cold air then until i get moving around /forums/images/graemlins/truck.gif
     
  4. Stephen

    Stephen 1/2 ton status Moderator Vendor

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    You can check the thermostat in a pan of hot water to make sure it's working right. It's typical to see fluctuations in water temp as the thermostat opens and closes, especially in cold weather where the water in the radiator can be really cold compared to the water in the motor, but if you're spiking that high, it sounds like the thermostat might be bad or your gauge might be wacky. You could test the gauge with a pan of hot water also. Take a pan of boiling water to the truck and the gauge should say that it's 200 to 240 degree.
     
  5. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    In my case I replaced my thermostat that had 7K miles on it with another one thinking the same thing. I boiled the old thermostat too and it worked fine.
     
  6. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    It sounds like you have an air block somewhere. The 6.2 coolant system holds something like 25 quarts, and at idle diesels run cold because they're using so little fuel. In 40 degree weather if I start my truck and let it run for 30 minutes the temp will not go about 130 or 140. To get to operating temps I have to drive it.

    From dead cold start it up without the rad cap on. As it gets hot wait for the coolant to start to run and as soon as it does the level in the rad should drop drastically. Fill it as it warms up. That should get the air out.

    Rene
     
  7. 78GMC1/2TON4x4

    78GMC1/2TON4x4 1/2 ton status

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    run for about 15-20 minutes? /forums/images/graemlins/truck.gif
     
  8. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    You said it heats up real fast...so it shouldn't take long for the coolant to start to 'run' inside the rad. With the cap off as soon as the coolant starts to 'run' just keep filling it, the level should drop pretty quick.

    Do not take the cap off a hot engine, take the cap off when it's cold and don't put it on until you've finished filling it.

    Rene
     
  9. 78GMC1/2TON4x4

    78GMC1/2TON4x4 1/2 ton status

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    earlier i let it suck its fluid in and filled it to the top to monitor it. was all fine. then started heating up and over flowing.....and im sorry...im not sure if the trucks heating up fast or if its just the old gauge...somethings haywire here....but then i took it out for a test run around town under 25, got back and it was mysteriously leaking again...sorry to confuse you /forums/images/graemlins/truck.gif
     
  10. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    Overflowing from where? Once you've filled it while it's running you'll need to put the cap back on securely.

    At any rate you should probably diagnose the problem in some sort of logical oder. Find the leak first, either get it fixed yourself or take the rad in and have it done. It will never hold proper pressure with a leak...and a leaking coolant system is not a sustainable situation. Have them pressure check the rad cap too.

    As Stephen mentioned test the thermostat in a pot of boiling water...I use a meat thermometer to see what the water temp is if and when the 'stat opens. Obviously it should open at the specified temp.

    Get a known working temp guage and sender on that thing so you can get an accurate read on engine temps.

    Make sure the heater core isn't blocked, anything restricting flow is bad.

    Check the clutch fan. When cold it should spin somewhat freely. As temps rise the clutch should engage the fan more and more. When it's warm and you shut it off the fan should be difficult to turn by hand.

    Is the factory fan shroud still there?

    A bit of a long shot, but the belts are tight enough? The water pump needs to be turning to work, same with the fan.

    Rene
     

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