Please help overheating issue - SOLVED

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LarryS999

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I have a 2001 Tahoe LT 2WD I bought in July of 2023 with 141k miles at the time. Current mileage is 150,031. I am now experiencing an issue were when say stopped at a long red light or such the tahoe will start to want to overheat. This started 4 days ago, and before this it never would reach 210 on the temp gauge would stay just shy of 210. Started doing this completely out of the blue with no warning. The tahoe does not have any coolant loss at all so far with this. But when parked you can faintly hear what sounds like the coolant gurgling or boiling for maybe 1 minute after shutdown. I have even used a block tester with the blue fluid to confirm no head gasket issues.

Now if stopped for say over 30 secs the temp starts to climb slowly and has gotten to 3/4 up the gauge but no higher I either raise the engine rpm or get the vehicle in motion to cool it down. I am mechanically inclined and decided as the vehicle is still new to me so to speak that I would go thru the cooling system to try to solve this. I also wanted to replace these parts as I didn't know the age of them, turns out it was all the factory original stuff except the fan clutch, dates codes on the parts proved that. The hoses had no dates codes but did have GM part numbers on all of them.

I have replaced the follow parts with Autozone parts, new gates serpentine belt, new water pump(dura last), new 187 temp thermostat(a motorad failsafe) new ac delco overflow cap, new upper and lower rad hoses(gates), new heater hoses(gates) and the plastic heater core connectors, a new coolant cross over pipe as there did appear to be a leak starting in the tiny rubber hose going to the throttle body, a new dura last brand fan clutch for ac equipped models.

The vehicle was well maintained by the previous owner who was also the original owner. It had dexcool in it and now has new dexcool coolant as well, a 50/50 premix. Only the radiator, coolant expansion tank, and heater core are now the original parts left of the cooling system I believe. I do plan on replacing the expansion tank soon as it is discolored slightly with age. I can see the date code on the radiator so I know it is the factory one but appears to be fine. Never appears to even have had an oil leak, it does have a GM rebuilt trans in it done at the dealer!

When I went to disassemble everything I did find that the rubber gasket around the inside of the thermostat was missing a small(maybe 1/4 inch long) piece of the rubber, this is the rubber seal inside the thermostat were it seals when the thermostat closes, not the gasket itself. There was a light discoloration of the inside of both rad hoses resembling rust in color but
I believe it is dexcool residue as that is what it smells like. The heater in this tahoe has never worked right in the nearly 1 year of owning it, acts like the heater core may be clogged. As it will only put out a small amount of heat if kept on fan speed 1, any higher speed and the air isn't warm. As I live in Phoenix AZ and it has seat heaters the heater not working wasn't an issue. While i had it apart I did try to flush out the heater core with the water hose and a nozzle but didn't seem to help.

If you have the AC on it will start to get hot faster than if the AC is not on but by only a few seconds. If you raised the engine rpm above 1500 for 15 seconds or so it will drop back below the 210 mark on the gauge. I know the gauge is correct as I have what is called a scan gauge ultra that plugs into the OBD2 port and gives various info including engine temps. I have the scan gauge as I also have a 2005 Colorado and the temp gauge in those trucks are not reliable. The scan gauge and tahoe's temp gauge reading match with each other.

The fan clutch I believe is working, can barely hear it at idle but a full woo at 2k rpm. With the engine running i feel plenty of air flowing if i place my hand behind the spinning fan. and It even blows out of the engine bay at you if your standing by the left front tire with the hood open and the engine idling. I have verified there is no obstructions behind the grill in front of the radiator/condenser and there is nothing between the rad and ac condenser. I also hosed out this area to remove any dirt but still no change.

I have bought a new radiator and plan to install that next to see if that could be it. There was no visible signs of dexcool mud in the system when I tore it down and the dexcool that came out appeared fine. I am only doing the radiator as I can't think of what else this can be. I even took the new fan clutch back and had it swapped for another one in case I bought a bad one no change. Could this be because I didn't use a AC delco fan clutch, the one that came on the tahoe was a no name one had a date code of 2018 on it. It also didn't make the woo noise at 2k rpm. I can clearly tell there is more air flow with the new clutch vs the old no name one.

Any help is greatly appreciated, I thank you all.
 

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Is the fan shroud complete and in place?

If so, I'd suspect the radiator, too. But be careful of aftermarket radiators as some don't have the correct restriction (orifice) in the fitting to the small hose that goes to the surge tank. There are a few threads on here about that (causes overcooling and not getting to operating temp, the opposite of what you have now).

EDIT: https://www.tahoeyukonforum.com/threads/07-tahoe-engine-hot-ac-turned-off.122990/post-1519742

If you do change your radiator, I wonder if you'd be willing to look at your OE radiator and measure that orifice so we know what OE is. Maybe use a few drill bits and tell us which one is a good fit, and what the next size up is that doesn't fit? I like empirical data.
 
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LarryS999

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Is the fan shroud complete and in place?

If so, I'd suspect the radiator, too. But be careful of aftermarket radiators as some don't have the correct restriction (orifice) in the fitting to the small hose that goes to the surge tank. There are a few threads on here about that (causes overcooling and not getting to operating temp, the opposite of what you have now).

EDIT: https://www.tahoeyukonforum.com/threads/07-tahoe-engine-hot-ac-turned-off.122990/post-1519742

If you do change your radiator, I wonder if you'd be willing to look at your OE radiator and measure that orifice so we know what OE is. Maybe use a few drill bits and tell us which one is a good fit, and what the next size up is that doesn't fit? I like empirical data.
Yes the fan shroud is in place both the pieces are fully in place and intact. I am hoping it is the radiator as I honestly can't figure out what else it could be. It runs perfectly with no power loss, burns less than half of a quart of oil between the 3k mile oil changes i do to all my vehicles. It even gets about 16 mpg in the city and i have gotten over 20 mpg several times on the freeway, which is better than my 4 cylinder colorado can manage. I will see if i can determine that orifice size your talking about when i get the old rad out.
 

nonickatall

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I would say you have lice and fleas.

As for your bubbling, I think it's more likely a defective cylinder head gasket. You don't have any loss of coolant, but your car blows into the coolant, and you have already replaced the suspicious parts such as the thermostat, water pump and overflow cap.

I also have a defective cylinder head gasket and did a CO test. I didn't measure any CO either. Maybe it just takes too long for the CO to reach the top of the expansion tank or you didn't do the test correctly, because you have to let the engine run for a while, until the CO finds its way out of the cooling system.

And I don't think you have a clogged radiator, because a clogged radiator doesn't happen spontaneously, it's a long process that mainly has to do with poor maintenance of the cooling system, which doesn't seem to be the case for you.

Your poor heating performance could of course also be an actuator problem.
 
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LarryS999

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Thought it would let everyone know I got it figured out turns out the brand new thermostat out of the box is junk it's not even opening up until it reaches 205 degrees yet it is a 187 degree thermostat. I tested it by putting it in a pot of boiling water. Used a thermometer keep track of the temp of the water as it heated up and finally at 205 degrees the thermostat started to open as the water reached a hard boil it finally opened all the way. So I'm replacing the thermostat with the 160° one. And for those who are interested the orifice on my original radiator date coded to 2001 a 3/32 drill bit fit in the orifice hole perfectly. I had already bought the new radiator I might as well install it at least and I know the whole cooling system has been replaced minus the heater core. I guess the motor rad fail safe thermostats are not as good as they used to be. I thank everyone for their help with this thank you.

I knew this had to be something stupid and simple and I wasn't going crazy.
 

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It could be, too, that the radiator was contributing by not being able to help lower the temp. And thanks for the 3/32" measurement!
 
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LarryS999

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True that is possible all I know is I just let it idle in my driveway for 30 mins after driving it for about 10 miles with the AC on max parked in the sun and it never even got the 210 on the gauge the halfway mark. So at least it fixed thank God. And since it's dark green in color almost black being in the sun with that added additional heat load because of the vehicle's color. Still stayed just shy of the 210 temp mark on the gauge. And currently it is 92 degrees hear in Phoenix.
 

Marky Dissod

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... for those who are interested, the orifice on my original radiator date coded to 2001,
a 3/32" drill bit fit in the orifice hole perfectly.
How does one go about SAFELY improving the size of this hole to 1/8"?
 

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