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Help with Over heating

Discussion in '1982-Present GM Diesel' started by TK5, Mar 8, 2004.

  1. TK5

    TK5 1/2 ton status

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    Here's the case. I was driving home the other day and everything was ok. Then the 6.2 started to overheat. I stopped to let it cool down and then added some water to make it home. It would get hot and then cool down, get hot cooldown. So I figured my thermostat was going bad. I pulled the thermostat to get home. I had been driving it a couple days back and forth to work so it never got hot (1 1/2 miles). I got a good Stant HD thermostat and put it in. I just can't seem to get the 195 degree thermostat to open in the 6.2. I pulled it out and placed in a pot, heated the water to make sure the stat was opeming. I didn't have a themometer to see what temp it was opening but it was opening when the water was heated. I placed it back in the 6.2, but i still can't seem to get the thermostat to open.

    I thought I might have an air pocket keeping the water from the stat and did everything to get it to work, still no luck. I was told I may have a cracked head, blown head gasket and other deals. I'm not convinced. The 6.2 runs smoothly, no evidence of water from the exhaust pipes, no water in the oil, No leaks from anywhere. I'm really confused right now.

    Amyone want to make a suggestion what i might look for or any suggestions. Anything would be greatly appreciated.
     
  2. OFFRDK5

    OFFRDK5 1/2 ton status Premium Member

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    Don't know if it is possible on one of these, but could you have put it in backwards?

    Alos about the getting hot, there are many factors involved.

    1. Outside temp?
    2. How fast were you going?
    3. Were you on the skinny pedal alot?
    4. How clean is your radiator?
    5. Pulling a load witht the rig?
    6. What kinda tranny you got in it? You have a tranny cooler that is blocking the radiator?
    7. Need a thermometer and test the radiator temp in the radiator and see if it really getting hot. Could be a bad sender or something.

    Just some questions/ideas.
     
  3. azblazor

    azblazor 1/2 ton status Premium Member

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    What is the ambient air temp? You can generate heat using the torque convertor, if you have a good parking brake set it hard and let the truck idle in drive (chock the wheels), or have someone sit in it with it in drive and the brakes on, while you watch down the open radiator fill hole and wait for the thermostst to open. Look for bubbles to see if a head is leaking. You can also cover the radiator with cloth or cardboard during the idle test or during driving to increase the temperature.
     
  4. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    Don't know if it is possible on one of these, but could you have put it in backwards?

    Alos about the getting hot, there are many factors involved.

    1. Outside temp?
    2. How fast were you going?
    3. Were you on the skinny pedal alot?
    4. How clean is your radiator?
    5. Pulling a load witht the rig?
    6. What kinda tranny you got in it? You have a tranny cooler that is blocking the radiator?
    7. Need a thermometer and test the radiator temp in the radiator and see if it really getting hot. Could be a bad sender or something.

    Just some questions/ideas.

    [/ QUOTE ]

    Yeah check the sender, I had a bad sender and it told me that the temp was fluctuating a lot up and down and I kept thinking it was untill the sender really messed up and the temp started jumping up and down.
    /forums/images/graemlins/thumb.gif
     
  5. tRustyK5

    tRustyK5 Big meanie Staff Member Super Moderator GMOTM Winner Author

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    [ QUOTE ]
    I just can't seem to get the 195 degree thermostat to open in the 6.2. I pulled it out and placed in a pot, heated the water to make sure the stat was opeming. I didn't have a themometer to see what temp it was opening but it was opening when the water was heated. I placed it back in the 6.2, but i still can't seem to get the thermostat to open.

    [/ QUOTE ]

    Until I've driven mine for 5 or 6 miles in traffic it doesn't get above about 160 F The other night I was coming home on the freeway...there was an accident and everyone had to exit and detour so it was pretty snarled. My temp guage read 195-200 cruising...and within 5-10 minutes idling while we were stopped the temp had dropped to under 160(ambient temp was ~ 50 F). These motors just don't seem to make much if any real heat while idling, and the cooling system is huge.

    Rene
     
  6. TK5

    TK5 1/2 ton status

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    [ QUOTE ]
    Don't know if it is possible on one of these, but could you have put it in backwards?

    Alos about the getting hot, there are many factors involved.

    1. Outside temp?
    2. How fast were you going?
    3. Were you on the skinny pedal alot?
    4. How clean is your radiator?
    5. Pulling a load witht the rig?
    6. What kinda tranny you got in it? You have a tranny cooler that is blocking the radiator?
    7. Need a thermometer and test the radiator temp in the radiator and see if it really getting hot. Could be a bad sender or something.

    Just some questions/ideas.

    [/ QUOTE ]

    I am getting a small of bubbling in the radiator.

    iwas doing about 65 mph.

    I replaced the thermostat, but i could tell it had not opened (temp about 220 on the gauge) I squeezed the upper hose it was very had like no waer was passing thru the hose.

    Radiator is clean. No load. Transmission is a turbo 350. 4.10 gears 315-16-75 tires. Dana 44 front-14 bolt rear.

    i don't really drive that fast. Traveling on the interstate about 65.

    Outside temp about 50 degrees.

    i have removed the thermostat and driving it now. i really don't want to get to far away from home.
     
  7. TK5

    TK5 1/2 ton status

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    I was also told to find someone with an emissions tester and place the nozzle inside the overflow tank, not in the water or antifreeze just inside the tank. the emissins teter will pickup any exhaust emissions from blown head gaskets that may be inside the tank.

    just a thought from a really good shade-tree mechanic.
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Your problem sounds very similar to an issue I was having with my 305 a few years back.....

    I swapped out the thermostat as part of a spring tune up and immediately afterwards my temp gauge started going a little crazy(hot/cold). It ended up being an air pocket that somehow wouldn't burp out. Here's what I did:

    After letting the truck sit overnight, I popped off the rad cap and started the truck. The rad was a little low so I toppped it right up. As the engine warmed up I started revving the motor up by hand every 30 seconds or so. When the T-stat opened the level in the rad dropped by a couple of inches. I immediately refilled the rad to full and ran it for about 2 minutes at around 2000 RPMS. Of course, the coolant kept on expanding and started overflowing out of the rad. I got my wife to put the rad cap back on and let off the revs, then took the truck for a 5 minute boot down the highway.....

    Theoretically, the rad was overfull. I expected to find a bunch of extra coolant in the overflow tank after my jaunt down the highway, but to my surprise, it only looked like I burped out a cup or two. And in the morning when I checked the reserve level, the rad had sucked the extra coolant back in!!!!!!

    That's how I got rid of the air in my system, brother. Hope that helps...

    Oh, one other thing- make sure that the hose that connects your rad to your overflow tank is always covered by coolant. If you let your overflow tank run dry, your rad will sip air when the truck cools down after you turn it off...... /forums/images/graemlins/thinking.gif
     
  9. dieselburban

    dieselburban Registered Member

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    tRustyK5 Thats the same thing my 6.2 does,I can leave it idle for a 1/2 hour and it wont open but after about five minutes on the road it will open,it sucks trying to defrost the windows in the middle of winter in Minnesota,and to top it its a suburban that has like a million cubic feet of room inside /forums/images/graemlins/doah.gifcold ride to work in the mourning /forums/images/graemlins/burb.gif
     
  10. arveetek

    arveetek 1/2 ton status

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    Starting to sound like a blown headgasket to me. /forums/images/graemlins/thinking.gif

    Here's one way to find out for sure: remove all the belts so that the water pump is not turning. Start the engine and watch for bubbles in the radiator. If bubbles appear, then it's a blown headgasket for sure. Of course, you don't want to run the engine for very long without the water pump operating.

    To narrow down which head is the culprit, remove the crossover pipe between the two heads. Now you can see the coolant sitting in each head. Again, start the engine without the water pump turning, and see which side the bubbles are coming from. Then you'll know which gasket to replace. Of course, if you're in it that far, it couldn't hurt to replace both of them anyway.

    I hope you don't have a blown headgasket, but it's starting to sound that way to me. /forums/images/graemlins/frown.gif

    The reason the upper hose felt hard was due to excess pressure in the system caused by combustion gases being forced into it. Same for the bubbles in the radiator. The temp. guage fluctuates not because it's actually hot, but because air bubbles are forming near the sending unit. When there's no water by the sending unit, the needle can go haywire, usually going to full hot. Again, the engine is not running hot, it's just excess air in the system. The reason it seems fine without the thermostat is because it lets all the air burp out into the radiator and out of the system. The thermostat traps it in the block.

    I know....been there done that...twice. Not on a 6.2L, but on my old 5.7L diesel. That's when I gave up and went to the 6.2L.

    Casey
     
  11. TK5

    TK5 1/2 ton status

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    I'm starting to think the same that i have a blown head gasket. I put in a 180 degree thermostat today instead of the 195 degree. it would fluctuate between the 180-200 range. The blazer was my daily driver becasue my van alternator crapped out me. First they gave me the wrong alternator, then gave me the wrong belt, gave me the right alternator and wrong belt in the right package. Finally the right belt. Advance Auto Parts was the culprit. The van is right now. i hope to dig into the Blazer again this weekend since i have some wheels that roll.

    Thanks to you all for help. I not a diesel mechanic but I've got a good start so far.
     

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