Please help!!

[OR VietVet]

Like has been mentioned by several people here, it sure sounds like a clogged radiator but could also be a failed water pump not moving coolant. At that age I would replace the radiator and even the water pump, if pump is original. Did not see what you said about that. Cooling systems are finicky but also very important. I bet your new head gaskets are bad now for sure. I replaced both of mine recently before they went bad eventually.

 

[OR VietVet]

By the way, I have never seen a flush fix a clogged radiator. The flush is supposed to be maintenance and not a repair.

 

[Doubeleive]

By the way, I have never seen a flush fix a clogged radiator. The flush is supposed to be maintenance and not a repair.

true but doing this may show if it has poor flow or not

 

[mike_whip]

The whole reason why they'll run cool without that restrictor, is that these engines run a 'reverse' thermostat. Instead of the tstat being on the output side of the water pump, it's on the inlet. Which means that the radiator is pressurized by the water pump the second the engine is turned on.

There's a bleed-tube on the top-pass side of the radiator that returns to the overflow tank. The end result being, there's always a little bit of coolant going through the radiator. Usually this is a net benefit - the system self bleeds, and does so very quickly. However if that restrictor is not in place, there will be more than a little coolant going through the radiator, wicking away more heat than was intended in the design. So no restrictor = too much flow through the self-bleed = too much flow through the radiator = cold

Now with that said... These systems are flippin' weird in that it uses the heater core lines to control the thermostat. So if your heater cores are clogged, or if you did a lazy bypass and just capped hoses - there won't be enough coolant going over the t-stat to appropriately regulate temperatures, and you'll get an overheat / hot condition even if everything else in the system works perfectly. This also goes for a partial clog. So if, for whatever reason, you wanted to bypass your heater core - you would loop a piece of hose around and just connect the waterpump to itself, NOT cap it off.

Couple bits come to mind, in no particular order

1. If you get heat when revved, the water pump is spinning. It's not air locked.

2. Double check coolant level in your reservoir. Low coolant is the first thing I'd be looking at here. Especially if you get any gurgling / waterfall type sounds from under the dash.

3. Verify your belt isn't slipping. From a cold start - let it run for a minute or two. Turn the engine off. Then go ***** the pulleys. Are any of them warm/hot?

4. How's that water pump looking anyway? I've seen some realllll bad aftermarkets. Some have a raw pump with no vane guide. Those are lame. My favorite was one that didn't even have an impeller on it... oops....

5. You can try back flushing your heater core. Disconnect the hoses and put a garden hose on it. The port on the rear of the engine is the outlet to the heater, front is the inlet to the pump

Thanks for all of this @SnowDrifter. After this weekend I can say that the fluid is full, the water pump is good to go, no slipping of belts and I flushed the heater core. As of right now, it is working as it should but I will keep everyone up to date. I wouldn't have thought about doing that if it wasn't for everyone on the forum. You guys rock!

 

[robhotdog]

Long time lurker and first time poster. Registered for an account tonight since I couldn't find an answer that I haven't already tried.

Backstore:
2006 Tahoe Z71 with 5.3 flex fuel
232,*** miles

I just did head gaskets, water pump, thermostat, every gasket that I could think of while in the motor, coolant flush, oil change, new belts, etc. Everything I would want a shop to do, I did it.

Everything ran great for the first 120 miles and then it started smoking. Replaced the faulty valve cover, which was the one with the outdated design, and that fixed the problem. Ran great the next 300 miles and then it started to overheat and read "coolant hot" so I shut her down and since I was a ways from home I got her towed.

Bled the system, replaced the thermostat again just in case and changed all of the fan relays as well. Idle stayed at 200-210 and then took it for a drive. Within 10 min, message popped up again that coolant was hot so I shut her down and waited til she was cold to drive her home since I was within a mile from the house.

Just replaced the thermostat again tonight with one that stays open in case of failure to cool the motor. Bled the system again and refilled to make sure there was no air bubbles. Started her up, idled for 25 min and all seemed to be good. I took her for a spin and within 2 miles it started to get higher in temps at about 250. Heater blew cold air for a little and then back to hot and then said "coolant hot" again.

I am at a loss with the rig. I am thinking maybe the brand new water pump went bad? Maybe its my fans (but they kick on as they should)? I honestly don't know.

Anybody have any thoughts on what it could be? I love the Tahoe but I am getting to the point to where I am almost ready to give it up.

Mike I'm a retired GM tech. First things first..why did you pull th heads?? You cannot reuse the head bolts!!! I use arp bolts now and use standard 3 step process for aluminum heads. Assuming you did that. You can tell if the tstat is open on most every car by feeding the upper hose.. if it's hot its open..now the fans are designed to come on at 230 off arround 190. Normal. Turn ac on and the fans should run with the compressor. Your hands can also feel the heater hoses for differences. I suspect if you idled for 25 min you had plenty of coolant. When its Overheating is the jar bubbling?? How hot did it get when you decided to do head gaskets? Was the engine missing? Lots of things to ck besides gaskets! You can dammage temp sensors by bad overheat. Its normal to replace them with tstat. I suspect head gasket problem with warped heads Idk. Your trying to fix the results without fixing the cause. Radiator clogged ? Same with heater core...good luck

 

[29tomt]

Long time lurker and first time poster. Registered for an account tonight since I couldn't find an answer that I haven't already tried.

Backstore:
2006 Tahoe Z71 with 5.3 flex fuel
232,*** miles

I just did head gaskets, water pump, thermostat, every gasket that I could think of while in the motor, coolant flush, oil change, new belts, etc. Everything I would want a shop to do, I did it.

Everything ran great for the first 120 miles and then it started smoking. Replaced the faulty valve cover, which was the one with the outdated design, and that fixed the problem. Ran great the next 300 miles and then it started to overheat and read "coolant hot" so I shut her down and since I was a ways from home I got her towed.

Bled the system, replaced the thermostat again just in case and changed all of the fan relays as well. Idle stayed at 200-210 and then took it for a drive. Within 10 min, message popped up again that coolant was hot so I shut her down and waited til she was cold to drive her home since I was within a mile from the house.

Just replaced the thermostat again tonight with one that stays open in case of failure to cool the motor. Bled the system again and refilled to make sure there was no air bubbles. Started her up, idled for 25 min and all seemed to be good. I took her for a spin and within 2 miles it started to get higher in temps at about 250. Heater blew cold air for a little and then back to hot and then said "coolant hot" again.

I am at a loss with the rig. I am thinking maybe the brand new water pump went bad? Maybe its my fans (but they kick on as they should)? I honestly don't know.

Anybody have any thoughts on what it could be? I love the Tahoe but I am getting to the point to where I am almost ready to give it up.

Are you seeing signs externally that it is overheating like steam or whatever? As another posted indicated, maybe a temp sensor?

 

[mike_whip]

Thank you for all of your help everyone and sorry for the lengthy absence. It was running well and then... it didn't. I had to go out of town and dropped it off at the shop so they can look at it and come to find out, I needed a new radiator. That was the last thing on the list to replace as I marked stuff off of the list. As the shop was flushing the radiator, they stated that there were large chunks of debris in the radiator. All is good now, runs great and I am so thankful for all of your input to help me figure this out. All of you are truly awesome and I am glad I joined the community.

 

[mike_whip]

Mike I'm a retired GM tech. First things first..why did you pull th heads?? You cannot reuse the head bolts!!! I use arp bolts now and use standard 3 step process for aluminum heads. Assuming you did that. You can tell if the tstat is open on most every car by feeding the upper hose.. if it's hot its open..now the fans are designed to come on at 230 off arround 190. Normal. Turn ac on and the fans should run with the compressor. Your hands can also feel the heater hoses for differences. I suspect if you idled for 25 min you had plenty of coolant. When its Overheating is the jar bubbling?? How hot did it get when you decided to do head gaskets? Was the engine missing? Lots of things to ck besides gaskets! You can dammage temp sensors by bad overheat. Its normal to replace them with tstat. I suspect head gasket problem with warped heads Idk. Your trying to fix the results without fixing the cause. Radiator clogged ? Same with heater core...good luck

Hey @robhotdog, thank you for your input! She is all fixed now

 

[CTUBS8732]

Have you checked you under the hood fuse box for burnt ports? I replaced whole cooling fan relay fuse box cause I had a similar issue. Problem solved for me.