2001 Tahoe Reverse Flow cooling system

[Big Mama]

Wife’s BMW had similar issue after flush and fill. Had to put front on a ramp to get all air out. It’d peg hot if I sat on even a slight incline.

 

[LanceLyons]

How old is your water pump?

I think that, unless the cooling system was horribly neglected, I kind of doubt the radiator is plugged internally.

Hi, I replaced the water pump on the tahoe probably 5 years ago. There is no leaks around the pump so unless it broke the impeller inside, I would think its ok. I just dont know how to test the flow. I really dont feel much flow inside the upper hose. I have disconnected the upper hose while running and it does eventually come out but it seems fairly slow.

 

[LanceLyons]

my first suspect would be the radiator, if it is over 5 years old then it's time to replace it, yes you might get flow in and out, that doesn't mean it is cooling properly the little fins can be clogged especially if it has not been maintained annually. the fact that it works ok with good air flow and not when just idling is a dead giveaway. just my opinion also when you cleaned it out do you think you might have removed the restrictor to the reservoir tank? take a look at the flow from the radiator to the reservoir if you see liquid moving quickly that is also a known problem.

So i am not completely following. When I pulled the radiator and flushed it with a garden hose from the top and it came out the bottom just as fast as going in. I assumed that meant it was able to flow ok. Am I wrong on that?

what do you mean about the flow from radiator to reservoir. how is that checked. I am only able to monitor the level in the reservoir. I do notice that when I rev up the motor and then release, I see bubbles coming up in the reservoir. I have pressure tested the system to 15 lbs with no problems.

 

[Doubeleive]

If the radiator fins are clogged the coolant will just flow thru the larger area's and the cooling effect of the radiator is reduced, it may work fine with good air flow but when you are stopped and just dependent upon the fan that is when you would notice the reduced efficiency. I have had it happen before more than a couple times like when you are sitting at a red light on a hot day and the temp starts rising up or sitting idling and the temp just slowly goes up and up and up. replace the radiator and whalaa problem gone.
disregard what I said about the restrictor I think if that was missing you would see a flow of coolant thru the reservoir and the effect would be the opposite (fail the heat up all the way, and it would run cold).
it's just my experience, if it is working normal while moving and then heats up when stopped the radiator would be my primary suspect. It could still MAYBE be your fan clutch but if you take it for a drive and then idle and pop the hood and have decent air flow and it's heating up I would say radiator.

 

[Larryjb]

When the fan clutch comes on, you should hear a roar, like you're driving a semi.

 

[LanceLyons]

When the fan clutch comes on, you should hear a roar, like you're driving a semi.

on the fan, this fan is directly on the belt system. I was told to test this, just look for how much slip or how much resistance the clutch provides. If the fan spins freely then it needs to be replaced but if it resists then its probably ok.

In my case when I try to spin the fan it quits turning in less than a quarter revolution. This seems to be OK.

What kind of flow should I have from the water pump? is that testable?


I do agree that everything seems to point to the radiator but the lone thing that has me questioning this is how I had to add coolant directly to the upper hose and into the motor to perhaps force some air pocket out. I should not have to do that. I ran the vehicle more than a dozen times with the reservoir cap off and running the car up to temp, etc. Shouldnt that have "burped" the motor and system?

 

[Larryjb]

... If the fan spins freely then it needs to be replaced but if it resists then its probably ok.

...

I do agree that everything seems to point to the radiator but the lone thing that has me questioning this is how I had to add coolant directly to the upper hose and into the motor to perhaps force some air pocket out. I should not have to do that. I ran the vehicle more than a dozen times with the reservoir cap off and running the car up to temp, etc. Shouldnt that have "burped" the motor and system?

On the fan, I've learned over and over that "probably" only applies to everyone else, and not to me! One way to test this is to use a piece of cardboard to block the radiator airflow and run the engine until the temperatures rise above 212. You should hear a new roar from the fan as the clutch engages.

Did you install an ACDelco water pump?

When you did the water pump, what did the cooling passages look like?

Also, what model/year are we looking at?

 

[Larryjb]

Check this out:
https://www.yourmechanic.com/question/vehicle-is-starting-to-overheat-at-idle-by-dustin-p

 

[Fless]

Not all fan clutches make a roaring sound. On mine, when it engages, you can hear more air being pushed, but it's in no way a roar. Mine is most likely an OE fan clutch.


From Haynes:

Engine-mounted fan and clutch Check

1 All V6 and V8 engines are equipped with thermostatically controlled fan clutches.

2 Begin the clutch check with a lukewarm engine (start it when cold and let it run for two minutes only).

3 Remove the key from the ignition switch for safety purposes.

4 Turn the fan blades and note the resistance. There should be moderate resistance, depending on temperature.

5 Drive the vehicle until the engine is warmed up. Shut it off and remove the key.

6 Turn the fan blades and again note the resistance. There should be a noticeable increase in resistance.

7 If the fan clutch fails this check or is locked up solid, replacement is indicated. If excessive fluid is leaking from the hub or lateral play over 1/4-inch is noted, replace the fan clutch.

8 Warning: If the fan is damaged in any way, don't attempt to repair it. Replace the fan with a new one.

 

[Fless]

If the radiator fins are clogged the coolant will just flow thru the larger area's and the cooling effect of the radiator is reduced, it may work fine with good air flow but when you are stopped and just dependent upon the fan that is when you would notice the reduced efficiency. I have had it happen before more than a couple times like when you are sitting at a red light on a hot day and the temp starts rising up or sitting idling and the temp just slowly goes up and up and up. replace the radiator and whalaa problem gone.
disregard what I said about the restrictor I think if that was missing you would see a flow of coolant thru the reservoir and the effect would be the opposite (fail the heat up all the way, and it would run cold).
it's just my experience, if it is working normal while moving and then heats up when stopped the radiator would be my primary suspect. It could still MAYBE be your fan clutch but if you take it for a drive and then idle and pop the hood and have decent air flow and it's heating up I would say radiator.

^^^^ THIS. If the fan clutch passes the test, pull the radiator and either get it to a radiator shop to have them rod it, or get a new radiator (with the integrated restrictor). New ones aren't all that pricey but it's your choice.

One other thing -- is the cooling system making its 15 psi? It's pressurizing with the cap on the surge tank?