Cooling fans constantly on

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Wes
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if it was showing the temp overheating and you just started it up after sitting for days then I would have to speculate the temp sensor is bad, the crack in the radiator oil cooler is not good either but if the coolant is full and the fans are running high speed right away then it's the coolant temperature sensor or water pump or thermostat is stuck. If it was going to overheat you would have had to have it running for a few minutes at minimum with no coolant flow, I just started mine up this morning after changing the radiator and it took it over 5 minute just sitting idling to even start to get up to normal temp, I had to rev it up a number of times as well. and this was with over 70 degrees ambient temp, my fans didn't even kick on until I drove it like a bat out of hell down the road and back and put the ac on, then they were only running on low speed.
 
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992dr

992dr

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In the last few days guys with two different brands of aluminum radiators have had theirs spring a leak. I'm a GM OE fan.

View attachment 372003
View attachment 372004

Send me your email and I'll send over the engine cooling file. Working on and just taking the Tahoe out for a drive can be a great stress reliever.

After hearing more about aluminum radiators leaking, I have decided to go OE.
I'll send you a PM now. I don't have a scan tool.
I agree, I certainly don't mind working on my Tahoe, it is one of the easier vehicles to work. But, with it sitting for so long I was really looking forward to taking it out for a drive. I also have a Charger that needs a little attention too haha. The joys of owning a higher mileage vehicle, I guess.

if it was showing the temp overheating and you just started it up after sitting for days then I would have to speculate the temp sensor is bad, the crack in the radiator oil cooler is not good either but if the coolant is full and the fans are running high speed right away then it's the coolant temperature sensor or water pump or thermostat is stuck. If it was going to overheat you would have had to have it running for a few minutes at minimum with no coolant flow, I just started mine up this morning after changing the radiator and it took it over 5 minute just sitting idling to even start to get up to normal temp, I had to rev it up a number of times as well. and this was with over 70 degrees ambient temp, my fans didn't even kick on until I drove it like a bat out of hell down the road and back and put the ac on, then they were only running on low speed.

Something is definitely off. I just ordered a new temp sensor. I had it running for a little while had to shuffle the cars around and get a few things ready to go. It was probably running for 10 minutes or so. But the fan or fans were on the entire time. Even when I drive, they're always on. The only time I hear one turn off is when I get home and park it. I'll go start it again just to see what happens. But they usually kick on shortly after starting it. I'll be back with more accurate info.
You just replaced your radiator?
 
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992dr

992dr

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Went out to start it and see what happened.
Started at 10:15 both fans turned on at 10:22 -+ low speed, it's about 80 degrees here. 10:24 both high speed fans came on and it started to over-heat going above its normal 210 range.
One thing I didn't pay attention to was the coolant level. It seemed low in the tank while it was running but it was already up to temps. When it cools down I will go check the levels.
 

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Went out to start it and see what happened.
Started at 10:15 both fans turned on at 10:22 -+ low speed, it's about 80 degrees here. 10:24 both high speed fans came on and it started to over-heat going above its normal 210 range.
One thing I didn't pay attention to was the coolant level. It seemed low in the tank while it was running but it was already up to temps. When it cools down I will go check the levels.
That is likely your smoking gun. If the coolant level is low, then it will also fool the temperature sensor which is by design, so it will kick on the fans to keep it from overheating. At no time does my coolant ever look low in the overflow tank, either before I start the engine, or while it’s running.
 

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Wes
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Went out to start it and see what happened.
Started at 10:15 both fans turned on at 10:22 -+ low speed, it's about 80 degrees here. 10:24 both high speed fans came on and it started to over-heat going above its normal 210 range.
One thing I didn't pay attention to was the coolant level. It seemed low in the tank while it was running but it was already up to temps. When it cools down I will go check the levels.
make sure it is full, start it up feel the big hoses, see if one is hot and the other cool
you can take the reservoir cap off on these pretty much anytime it might let a little pressure out if at normal temp while twisting the cap off
 
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992dr

992dr

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That is likely your smoking gun. If the coolant level is low, then it will also fool the temperature sensor which is by design, so it will kick on the fans to keep it from overheating. At no time does my coolant ever look low in the overflow tank, either before I start the engine, or while it’s running.

I'm heading back out there to check the levels now.
 
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992dr

992dr

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make sure it is full, start it up feel the big hoses, see if one is hot and the other cool
you can take the reservoir cap off on these pretty much anytime it might let a little pressure out if at normal temp while twisting the cap off

Gotcha, I'm heading right now to check.
 
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992dr

992dr

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WT*, No coolant in the overflow tank.
I don't see any spots on my driveway.
Hopefully I'll be able to grab a new radiator this week. Probably plan on changing my oil in hopes of not finding any coolant in there.
I'm just not prepared for this right now.
 

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Wes
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WT*, No coolant in the overflow tank.
I don't see any spots on my driveway.
Hopefully I'll be able to grab a new radiator this week. Probably plan on changing my oil in hopes of not finding any coolant in there.
I'm just not prepared for this right now.
coolant can be leaking from a variety of places and presuming the leak is slow enough the wind can make it blow away and never leave a drop.
best place to start is under the truck with a flashlight and look up
look under where the radiator sit's
look under the water pump (might need a mirror to see properly)
look under where the hoses & heater hoses are (especially where they "T" off at the firewall)
look under the reservoir tank area
look under in the rear passenger corner where the rear heater is
from up top look down the left & right sides of radiator
remove the plastic cover over the radiator support and look down between the ac & radiator
unbolt the fan shroud "13mm" and push it back a little and look down in back of the radiator
check the steam crossover pipe it sits on the top front of each head and passes under the throttle body, depending on the year there may be a steam pipe or caps on the rear of each head as well. follow the tiny hose from the radiator to find it.
 
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992dr

992dr

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coolant can be leaking from a variety of places and presuming the leak is slow enough the wind can make it blow away and never leave a drop.
best place to start is under the truck with a flashlight and look up
look under where the radiator sit's
look under the water pump (might need a mirror to see properly)
look under where the hoses & heater hoses are (especially where they "T" off at the firewall)
look under the reservoir tank area
look under in the rear passenger corner where the rear heater is
from up top look down the left & right sides of radiator
remove the plastic cover over the radiator support and look down between the ac & radiator
unbolt the fan shroud "13mm" and push it back a little and look down in back of the radiator
check the steam crossover pipe it sits on the top front of each head and passes under the throttle body, depending on the year there may be a steam pipe or caps on the rear of each head as well. follow the tiny hose from the radiator to find it.
I appreciate the info Wes, this will be my project for this coming weekend. I'm just hoping to be able to get parts in time.
I did notice moisture from the front passenger steam line above the head, looks like the head is pretty dirty because of it. I will most certainly dive deeper when I have it up on stands and the weekend to work on it.
Thanks again:cheers:
 

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