Coolant Temp Elevated

[gkonsite]

Original Owner: 2003 Cargo 129,800 Miles; Van Location: South Florida

First ever coolant flush 4/2018 at 101,798 Miles. Original and current coolant is Dexcool. Note: Water temp normal both before and after flush.

Historic coolant temperature (depending on outdoor temp) has been 195 to 210 degrees.

This past summer the temperature increased; 225 to 230 degrees at highway speeds and in stop & go traffic 235 degrees and higher. I’d have to turn on the heater periodically to keep it out of the orange.

I recently installed a new 195 degree thermostat and a new 16 psi cap. Dexcool was drained and refilled with new. Test drove vehicle (40 mph). When the water temperature gauge reached 195 the needle stayed at 195, and after a couple of miles the temperature began to increase gradually. New thermostat & coolant made no reduction in water temperature.

Note: AC blows COLD at all speeds. Fan clutch has resistance and rotates about ½ revolution when spun. Heater blows hot.



Drained coolant, disconnected radiator inlet & outlet hose and back flushed radiator. Bits of ‘crud’ came out but not an excessive amount.

Removed front grill and removed all dead bugs and bits of sand, etc. from AC condenser coil. Sprayed AC condenser with coil cleaner. Before external water flush of condenser, a stiff piece of cardboard was inserted between condenser and radiator. Condenser was flushed numerous times and blown out with compressed air. Same was done to the radiator, but from back to front.

Unrelated: Installed new belt tensioner, idler pulley & serpentine belt.

Cleaned coolant recovery bottle and filled cooling system with distilled water. Drove vehicle 20 miles and turned heater on & off several times.

Drained distilled water, which was darkened from residual coolant.

Refilled system with NEW Dexcool and test drove. Under all driving conditions (outdoor temp 85 to 88) the temperatures are now less (see photos), but still elevated. Also, the heater was no longer blowing hot.

Disconnected heater supply & return hoses. When the supply hose was removed the pipe was obstructed with what appeared to be rust flakes. Back flushed heater core and a good amount of crud came out. Heater now blows HOT.

Water pump impeller appears okay, otherwise the heater wouldn’t blow hot. The fan clutch appears to be working. If not, the AC wouldn’t blow cold at idle. Finally, at idle the radiator inlet hose is 210 degrees and outlet hose is 180 degrees.

Any suggestions? Thanks!

[MountainManJoe]

You could try using an infrared thermometer gun to check the radiator in multiple spots. It sounds like you had a lot of debris in the system which could have clogged areas of the radiator. But you are shedding 30 degrees through the radiator which is a healthy amount.
I presume you checked the condition of all the hoses, and haven't noticed leaks. Still a pressure test is something you could tick off the list. Sometimes you get cracks right in the radiator neck.
I can't remember if the 4.3 had a bleeder or not, but you need to make sure you burp all the air out. Try getting the engine hot, then park it on a steep incline for a while so all the air rises to the radiator neck .
Make sure the sealing surface for the rad cap is smooth and not pitted. If you take it off with a hot engine, you should hear built up pressure escaping.
You'll also want to make sure that when the temps are getting high, that the cooling fan is coming on full speed.
The other possibility is that the head gasket is going. 20 year old Dexcool sitting in the engine becomes caustic and will start to attacking gaskets. It ate the intake gasket on mine. That stuff was meant to be changed out AT LEAST every 5 years. They have testing kits for that.

[WoodButcher]

Did you flush the cooling system other than just fill and drain? if your heater core had blockages I would suspect blockages in the engine also.

[gkonsite]

Based on both of your replies and my suspicions, looking like cooling system flush I did with only distilled water was not adequate. Can either of you recommend a good flush product?

[WoodButcher]

Prestone sells a kit w/ adapters for a garden hose that is convenient but myself have always used dishwasher detergent and fittings I have laying around.

[MountainManJoe]

I've never needed such a product, but I have seen them on shelves.
I think the key ingredient is just going to be volumes and volumes of water. And pressure. I wouldn't even bother with distilled water. I have never used distilled in my life and had zero issues. (unless maybe you have extremely hard water)

I posted my procedure here: MountainManJoe @ Flushing cooling system

[WoodButcher]

I had problems with a Buick many years ago, the dexcool wasn't changed in it's life or maybe someone mixed products but the previous owner added stopleak. It was a mess. After a new radiator I flushed. Put a tee for a garden hose in the heater hose, took out the thermostat and filled with water and flush, idled in the driveway for thirty minutes, let it cool a little, drain, then I let it run with the garden hose wide open draining out the fill cap. I ran a flush through it three times, twice the off the shelf stuff and then the dishwasher detergent. Guy at napa told me when I went back to buy the second bottle he mixed a cup of that powder into a gallon of water. It finally came clean enough after running plain water for a few miles that I felt confident enough to put the thermostat back in and refill w/ antifreeze.

https://www.wikihow.com/Install-a-Coolant-Flush-Kit

the prestone kit
https://prestone.com/product/prestone-flush-n-fill-kit/

[MountainManJoe]

I received a question via PM: "do I need to remove the thermostat when flushing the coolant"
It's a good question so I'll answer here for everybody's benefit.

I did not. By running the engine, water is pumped into the engine block and out the heater assembly, and it worked well enough for me.

If you wanted to do a very thorough flush , you could add a step after flushing the heaters and re-attaching the heater hoses:
1. remove upper radiator hose from thermostat.
2. remove thermostat
3. run the engine while feeding water into the open end of upper radiator hose, until it runs clear.

You could also refill the system using only water, then go for a brisk drive, making sure the engine reaches operating temperature. Then dump all the water. Rinse & Repeat as necessary until water runs clear.

[WoodButcher]

That's it Joe, in the case of that Buick there was a sludge like film on the inside of the rad cap, rad, hoses, overflow tank, everywhere. I ran it w/o the thermostat until I knew for sure I wouldn't be wasting any more cash on antifreeze or parts.
A simple drain and refill I consider maintenance I'll do on any engine I've put 50,000 miles on like oil changes or any fluid that should be maintained. If it isn't causing you problems there is no need to go as far as I did then.

[gkonsite]

Thanks for the advice! It'll be a few days before I can do the flush. Update to follow! Also glad to have found this forum!

[Partychief1971]

I’m not sure if anyone suggested this but my 2005 Tahoe was overheating ,I replaced the water pump and gasket,The gasket was definitely leaking,and it still overheated.I checked YouTube and found that if the overflow tank,to radiator hose gets clogged at the radiator side your truck will overheat.
I pulled the small hose off of the top of the radiator and drilled the opening with a small drill bit and heard a sucking noise.and voila,problem solved,no more high temperature,the new water pump was good insurance too.(note,this was my 2nd water pump and I probably didn’t need it)
Hose is right at the top of the radiator on my Tahoe,looks like the same as your van

[WoodButcher]

Good tip chief, something not many of us check.