2000 Yukon-Long warm up time - partial heater core restriction possibly?

[OneofFew]

If the engine cools off while idling, I'd be looking at the fan clutch. It may be seized. If the engine warms when stopped, but cools when driving, that's an indication for a stuck open thermostat. Both are easy to replace.

 

[UmmScott]

Ill take a look this weekend if i have time. Yall know how it is this time of year. Holidays and everything is hectic.
I know for sure the fan clutch is not seized but... i dont like that it keeps ramping back up somewhat at idle.
It will disengage when the rpms go above 1.2k after about 7 seconds but at idle it does seem to speed back up.

Dont really like that. But im planning on getting electric fans next year anyhow

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[UmmScott]

Hope u all had a great holiday time with friends and family.

Had to do an emergency brake pad slap on the rear of the Yukon. Just pads for now till summer when i put a kit on it.
Anyhow...had time to look at the heat and check things out. It was 17F this morning and VERY Windy. Pulled into the garage and started it up and let it run for a couple mins.

After 10 mins (both heaters on low) this is where i was. Pics are attached.
What i noticed was the upper rad hose was getting warm along with the drivers side tank on the radiator. Not as warm as the heater hoses.
There is definitely a temperature difference between the 2 heater hoses. I can definitely tell that.
Those bypass hoses, is the one that goes to the overflow tank the one that needs a restriction inside it?
When i revved up the engine i could definitely see surges of coolant going thru that small hose into the top of the tank.
I do not know if the radiator is original or not. All the hoses look original for sure.

So....possibly a leaking by thermostat since the drivers side rad tank is getting warm?? Thats my thinking.
What do u guys think?

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[UmmScott]

To restate...
Only reason I'm not thinking its Not a thermostat is because it does get up to 195-200 on the highway. Just takes forever it seems.
And the heat is never very Hot...its kinda lukewarm to warm at best.

Just trying to remember... my mom used to have an 03 burban and that thing would get nice and hot

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[Fless]

Hopefully you're running that tank with the proper cap on it. If not, all bets are off. That in and of itself could be the cause of the cool temps.

The smaller hose that goes from the radiator to the tank is the one that needs to be restricted somewhat (circled in green below). With OE radiators that's done at the radiator, but you can pinch that line down some, maybe with a small valve or hose reducer.

 

[Danno34]

My bad yes you did say you weren’t losing any antifreeze. I should’ve been more descriptive in what I meant. Sorry about that. In my case I was suspicious that I was losing coolant because of anti freeze residue on other parts under the hood but I wasn’t losing enough anti freeze at first to even notice until obviously it all just came spilling out at once while idling in Park. Strange thing is though even what you where explaining with the hoses and the different temps between the 2 hoses, the luke warm air at best, car not over heating (yet) etc was what I experienced as well and I too didn’t think it was the water pump either until it crapped out all at once. Maybe the pump is technically still pumping yes and but perhaps it’s in its beginning stages of failing. Just an idea. Let us know what happens def curious. Wish you the best brother.


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[UmmScott]

I do have the correct cap. It says 15-16psi.

Ill look into this some more. I will pop off that bypass hose and see if there is a restrictor at the radiator. If there is not then I'll fix that issue and retest.
If there is a restrictor there still, then its gotta be thermostat or partially plugged up heater core.

I went thru the maintenance records from the previous owner (who took VERY good care of this truck) and there are multiple mentions of lack of heat, having the heater core flushed/backflushed, and thermostat replaced. I have checked the blend door as well and all is good there.
Is it the right thermostat? I dont know.. if i replace it I'll get a factory one.
Maybe the stat opens and regulates fine but wont fully close and is leaking by thru the radiator slightly

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[OR VietVet]

Does the replacement of the radiator ever come up in the maintenance records? You don't even have to remove that hose. Just use a small clamp on that hose and restrict it and if the problem goes away it is the aftermarket radiator that is the problem. You can do the quick easy fix with just leaving the clamp on.

 

[UmmScott]

Dealer wants $193 for the thermostat
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[OR VietVet]

Dealer wants $193 for the thermostat
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That's one of those new thermostats that installs itself. Open hood, set the thermostat parts on top of the radiator cover, go inside for 1 hour and come back out and viola!, it is installed and rechecked for any leaks.