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  1. #1

    Default Over Cooled? Please HELP!

    I have a 1992 GMC Suburban 1500 5.7L. The radiator started leaking last month so I replaced it (With the exact same radiator) along with the upper and lower radiator hoses and the thermostat (195 degrees) The temperature should run between 195-200 as it has for the last 4 years I have had it. It no longer does. The temp will climb Under Heavy load only. it will not climb at all just in idle. Under heavy load it will climb to 195 or close to that and then almost immediately drops back to 100 degrees (even if I'm still under heavy acceleration) it does this every few seconds (every 45 - 90 seconds) constantly. The heat will get warm and then cold and warm again over and over but never really gets Hot like it used too. There are no leaks in the coolant system. There is no coolant in the oil, there is no oil in the coolant, there is no mysterious coolant loss. Just as the truck seems to warm up the temp drops like a rock. If i block off anymore or the radiator there will be no air going through it... Please Help this is driving me crazy (and I'm cold )

    So far I have replace the thermostat (twice in the last month) I have blocked off 85% of the radiator with cardboard and still no success. The rear heat almost never works at all. This over cooling problem seems worse the colder it gets. I live in South Dakota so it can get -30 to -40 and sometimes even colder, but I have never had this problem before with this suburban or any of my other GMC / Chevy trucks.

    Please help me

  2. #2
    Jr. Apprentice fairyandtroll's Avatar
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    Default

    It's quite possible that the water pump is going bad. If your original radiator had separation problems inside it it could have damaged the pump or possibly contaminated the radiator. I would first back flush the radiator ( you can get the back flush kit and chemical at any parts store). and run it a bit 10 miles or so should do the trick, if no heat comes from the rear vents then let it cool and check the pump. One way I fund to check the pump is to carefully unhook the belt from it and rotate the pump sprocket back and forth in your hand listening for any kind of scrubbing noise and a scratchy vibration coming from it if no noise try spinning it fast with your hand if it turns more than 3 or 4 turns then it may be bad - a little resistance is what you need but too much is no good., make sure not to have any back ground noises and DONT crank the engine at any point till the belt is placed back! If it makes a scrubby or scratchy sound then I would replace the pump a weak pump will barely push water in to the radiator let alone through the rest of the vehicle. I hope this helps!
    Let us know if it does or not.
    The object is not to play the game, the object is to make it work!:glasses:

  3. #3

    Default

    Hmmm whats the fan doing all this time? Could it be running and pulling air through the radiator? I'm just throwing out a guess here, I've never had a vehicle cool to much.

  4. #4

    Default

    Not sure if the Rear vent heat and the Radiator issues are related.

    The too cool RAD might be a bad Coolant Temp Sensor.

    The no heat issue could be the Heater Core.
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  5. #5

    Default

    did you bleed the cooling system? did you add 50/50 antifreeze?

    do a resistance check on the coolant temp guage
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  6. #6

    Default

    Thanks for all the Info and suggestions Im gonna try a few of them with in the next few days.

    Quote Originally Posted by fairyandtroll View Post
    It's quite possible that the water pump is going bad. If your original radiator had separation problems inside it it could have damaged the pump or possibly contaminated the radiator. I would first back flush the radiator ( you can get the back flush kit and chemical at any parts store). and run it a bit 10 miles or so should do the trick, if no heat comes from the rear vents then let it cool and check the pump. One way I fund to check the pump is to carefully unhook the belt from it and rotate the pump sprocket back and forth in your hand listening for any kind of scrubbing noise and a scratchy vibration coming from it if no noise try spinning it fast with your hand if it turns more than 3 or 4 turns then it may be bad - a little resistance is what you need but too much is no good., make sure not to have any back ground noises and DONT crank the engine at any point till the belt is placed back! If it makes a scrubby or scratchy sound then I would replace the pump a weak pump will barely push water in to the radiator let alone through the rest of the vehicle. I hope this helps!
    Let us know if it does or not.
    I went ahead and got a new pump (Only $23.00) so I will be replacing that in the next few days. I also got the stuff to flush the system.


    Quote Originally Posted by tbplus10 View Post
    Hmmm whats the fan doing all this time? Could it be running and pulling air through the radiator? I'm just throwing out a guess here, I've never had a vehicle cool to much.
    Fan starts turning as soon as the truck is started. It's not pulling much through the radiator because 80 + % of the radiator is blocked with cardboard.

    Quote Originally Posted by ejohnson03 View Post
    Not sure if the Rear vent heat and the Radiator issues are related.

    The too cool RAD might be a bad Coolant Temp Sensor.

    The no heat issue could be the Heater Core.
    I also though the heater core my be partially bolcked or restricted. I got some system flush to see if that helps. A new heater core is only $34.00 so I can go that route if I need to. I doubt it's the Coolant Temp Sensor because the loss of heat coincides with the drop in temperature showing on the temperature gage (every time).

    Quote Originally Posted by Loggerhead Mike View Post
    did you bleed the cooling system? did you add 50/50 antifreeze?

    do a resistance check on the coolant temp guage
    Not sure exactly how to "Bleed the system" I have been told a few tricks like turn the radiator cap one notch so it's at 8LBS and not 16 and run engine to operating temp. Been told to leave radiator cap off and do the same thing (resulted in a spill and me having to add more coolant) I have been told to do both of those but when the trucks front end was inclined. No success with any attempt.

    No I don't use a 50/50 (-34) mix that is not enough protection here in South Dakota. I use the Max 70/30 mix (-84) the temp here can drop to -30 and -40 with no wind chill so a 50/50 mix at -34 degrees in not good enough. temps can get -55 to -75 degrees with the wind chill. I have been told that the wind chill has no effect on the coolant freezing point, and I say BS... Twice last year my radiator froze when the wind chill dropped to -52 and the ambient temperature was only -30... So I say BS. That is probably why I had to replace the radiator this year. I just didn't notice the small leak until i saw green snow this winter. Not to mention this truck may get driven 5 miles a week in the summer.

    No I have not done a resistance check on the coolant temp gauge. I'm not sure I know how or have the tools to do that. As I said previously I don't think it is the sensor because the loss of heat coincides with the drop in temperature showing on the temperature gage (every time). I'm not saying it cant be the sensor I just don't think the sensor would cool the coolant or cause the heater to blow cold. the upper radiator hose is cool to the touch also, it will only get warm to the touch for a split second or so. I can open the radiator at idol when the temp gauge drops and touch the coolant with my finger and its not even warm, even if the truck has been running for an hour, as long as its at idol and the temp gauge has dropped (or not climbed at all) the coolant in the radiator is always cool to the touch. It is circulating I can feel it, but its cool.

    Thanks for all the help I will keep you posted.

  7. #7

    Default

    [QUOTE=tbplus10;225431I've never had a vehicle cool to much.[/QUOTE]

    Yeah, that is usually a desired "problem", lol.

  8. #8
    Jr. Mechanic
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    Default too cool

    When I replaced my intake gasket, radiator, thermostat and water pump I wound up with a similar problem that it would only get to about half running temperature. I found debris stuck in the thermostat that was holding it open only about one thirty second if an inch but that was enough to let too much coolant flow and keep the truck running too cool. I changed it and still had the problem. After endless troubleshooting I pulled the thermostat again and found it had happened again (DOH!!!) so after a thorough flush every thing has been doing fine ever since.

  9. #9
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    You need to power flush any time you replace a radiator, so that all the old crap is out of the system. just because the T-stat is new dont overlook that either, they can fail quickly.
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