1992 Suburban Over Cooled? Please Help

[cibermap]

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 at 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

 

[Molson02536]

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 at 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)

Make sure your coolant is at the right mixture of 50/50 water/antifreeze, you can also go to a 40/60 water/antifreeze and try using a fail save thermostat. Also air in the cooling system will cause the problem your having, make sure there is no air gaps in the cooling system. Try running around town with the radiator cap only on the first click so the cap only holds 8psi, that would make any air in the system exit out through the cap and in to the over flow tank. Make sure that you have the heater in the front and rear set on the highest setting so the coolant will flow throughout the entire system. Once the engine cools, any fluid lost will be taken from the over flow so keep an eye on that and fill as needed. The only other thing i can think of is your water pump is weak and will need to be replaced soon. Good luck and keep us all posted. P.S, don't block off the radiator, it just makes it worst.

 

[cibermap]

Make sure your coolant is at the right mixture of 50/50 water/antifreeze, you can also go to a 40/60 water/antifreeze and try using a fail save thermostat. Also air in the cooling system will cause the problem your having, make sure there is no air gaps in the cooling system. Try running around town with the radiator cap only on the first click so the cap only holds 8psi, that would make any air in the system exit out through the cap and in to the over flow tank. Make sure that you have the heater in the front and rear set on the highest setting so the coolant will flow throughout the entire system. Once the engine cools, any fluid lost will be taken from the over flow so keep an eye on that and fill as needed. The only other thing i can think of is your water pump is weak and will need to be replaced soon. Good luck and keep us all posted. P.S, don't block off the radiator, it just makes it worst.

Yes I tried the radiator cap and have been told there might be air in the system. I have tried every trick that has been told to me, Radiator cap @ 8 LBS, Radiator cap off completely, Front end inclined with the radiator cap @ 8 LBS and then off again. All this has managed to do is spill coolant and require me to add more. I thought it also might be the water pump but the more I think about it wouldn't a bad or weak water pump make it Over heat by not circulating enough coolant? You can almost tell when the thermostat opens all the way because the temp drops so fast its like the rush of colder water closes the thermostat again... its a never ending cycle. I blocked off (Most) the radiator because the engine is too cold it's like the radiator is cooling too well and by the time the thermostat opens the water is so cold it closes it almost immediately. This is just what it seems like to me with the temp climbimng and droping so fast and so often.

 

[Molson02536]

Yes I tried the radiator cap and have been told there might be air in the system. I have tried every trick that has been told to me, Radiator cap @ 8 LBS, Radiator cap off completely, Front end inclined with the radiator cap @ 8 LBS and then off again. All this has managed to do is spill coolant and require me to add more. I thought it also might be the water pump but the more I think about it wouldn't a bad or weak water pump make it Over heat by not circulating enough coolant? You can almost tell when the thermostat opens all the way because the temp drops so fast its like the rush of colder water closes the thermostat again... its a never ending cycle. I blocked off (Most) the radiator because the engine is too cold it's like the radiator is cooling too well and by the time the thermostat opens the water is so cold it closes it almost immediately. This is just what it seems like to me with the temp climbimng and droping so fast and so often.

Cooling system on your Suburban works this way, the water is constantly being circulated from the engine block through the water pump, heater hoses, hater core, then back thought hater hose, to the water pump and then engine block. When the engine coolant reaches the temperature that the thermostat is set for to open, it opens and draws out the hot coolant and circulates it with cooler temperature coolant from the radiator to cool down the engine. With knowing this, your going to have to see if there is any restrictions to your heater hoses that is keeping the coolant flowing throughout your heater cores causing the engine to spike up in heat causing your thermostat to open and close and that your not getting good heat in your Suburban any more. This is why i'm wondering if your water pump may be go bad and is getting weaker can is not pushing the coolant through the heater core at a flow rate it needs to. Keep me posted and let me know what temperature your heater hoses are at going to and from the heater core, one should be hot and the other should be warm or cold if your have your heater set on high. This is how the cooling system keeps the engine temperature steady without it spiking up and down as you noted

 

[Molson02536]

Food for thought cibermap, did you replace the temperature sensor??? You may have a faulty temp sensor too if your getting good heat from your heater core. Your engine my not be spiking as bad as your gauge is indicating if the engine temperature sensor unit has gone bad. They do also fail due to corrosion and will start giving the wring signals to the gauges causing wrong or erratic readings.

 

[plein-gaz]

Juste comme ça, avez-vous déposez le thermostat de la bonne manière?

 

[cibermap]

Thanks for all the input and suggestions!

Cooling system on your Suburban works this way, the water is constantly being circulated from the engine block through the water pump, heater hoses, hater core, then back thought hater hose, to the water pump and then engine block. When the engine coolant reaches the temperature that the thermostat is set for to open, it opens and draws out the hot coolant and circulates it with cooler temperature coolant from the radiator to cool down the engine. With knowing this, your going to have to see if there is any restrictions to your heater hoses that is keeping the coolant flowing throughout your heater cores causing the engine to spike up in heat causing your thermostat to open and close and that your not getting good heat in your Suburban any more. This is why i'm wondering if your water pump may be go bad and is getting weaker can is not pushing the coolant through the heater core at a flow rate it needs to. Keep me posted and let me know what temperature your heater hoses are at going to and from the heater core, one should be hot and the other should be warm or cold if your have your heater set on high. This is how the cooling system keeps the engine temperature steady without it spiking up and down as you noted

Thank you. That make sense about the way the system is cooled, and why a bad water pump may be the problem.

Food for thought cibermap, did you replace the temperature sensor??? You may have a faulty temp sensor too if your getting good heat from your heater core. Your engine my not be spiking as bad as your gauge is indicating if the engine temperature sensor unit has gone bad. They do also fail due to corrosion and will start giving the wring signals to the gauges causing wrong or erratic readings.

No I didn't replace the temperature sensor, because i don't have good heat. Every time the temperature drops on the gauge the heater blows cold they are very well in sync. When the truck is at idol even if it has been running for hours I can open the radiator and touch the coolant with my finger and its cool. I can feel it circulating but its cool, maybe lukewarm if I'm lucky. So i dont think its the sensor because it says its cool and it is in fact cool. The upper radiator hose is also cool to the touch it may get warm when the thermostat opens but only for a few seconds the cool again.

No I don't use a 50/50 (-34) antifreeze mix that is not enough protection here in South Dakota. I use the Max 30/70 water/antifreeze mix (-84) the temp here can drop to -40 and -50 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, but I say BS... Twice last year my radiator froze when the wind chill dropped to -52 and the ambient temperature was only -25 to -30 but the truck was head on in the on comming 40MPH wind... So I say BS on the no effect wind chill. 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 only get driven 5 miles a week in the summer.

I did however get a new water pump (only $23.00) and some system flush, Hopefuly if my heater core is only partially blocked or restricted then it will clean it out and the new pump will have the power to move the coolant better.

Hoping to put the new pump on in the next day or two I will keep you guys posted...