Sierra running hot Thermostat question

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njss

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Today my 2000 5.3L Sierra started running warmer then it ever has except when a hose broke. The AC was on but it always is. With the AC off it runs the normal temperature.

The coolant level is good and not DexCool, and the oil level is good. Should I assume the thermostat needs replacing? Any tips or diagrams would be appreciated because I'd like to do it myself rather then take it in.

Thanks
 
It's acceptable for the coolant temp to run higher during hot weather and especially with the a/c on. The a/c condenser is dumping hot air in front of the radiator. Essentially, it's adding heat to your engine coolant. You didn't supply us with any temp #'s. What's the outside temp. What temp is the coolant. Do you trust your temp gage?
 
What do you mean by "The coolant level is good and not DexCool"?

GM vehicles MUST use DexCool. DexCool is designed to be used because of the aluminum heads and/or blocks. I am no DexCool expert, but can that be the problem?

Thermostats are known to give, since they are brass and spring loaded. They usually lock up, and coolant can't pass by into your engine. Replacing your thermostat, thermostat housing, thermostat gasket, and O-ring is very simple (just two bolts), just remember to also use Water Pump Sealant by Permatex (Gray).
 
dirtclod said:
It's acceptable for the coolant temp to run higher during hot weather and especially with the a/c on. The a/c condenser is dumping hot air in front of the radiator. Essentially, it's adding heat to your engine coolant. You didn't supply us with any temp #'s. What's the outside temp. What temp is the coolant. Do you trust your temp gage?
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The outside temperature was 85, the gauge reading was 230. The truck has always ran at 190 in any conditions. I drove to work and back today which is 15 minutes on the freeway. The truck ran at 190 without the AC off. Tomorrow I will try it with the AC on.

I'm also 100% sure you can run dexcool or conventional anti freeze. If you switch just do a complete flush. A second flush may be necessary after some time as well. If this is inaccurate please post the info.
 
At this point, I'm with cal roofer as far as installing a new thermostat. It's quick, easy and cheap. I stopped using dexcool, like you did. I'm not a chemical engineer. I'm a nobody and I just didn't like the residue dexcool left behind.

230 degrees with 85 degree ambient seems a bit high to me. I'd be starting with a radiator flush, a new t-stat and cleaning/inspection of external radiator fins. It's a pain in the rear but they do get dirty. Use a brass brush all the outside of the radiator, everywhere that you can reach. Then use a garden hose to spray any debrie out. Don't use a pressure washer, it's too powerful.

2 other things immediately come to mind. Clogged radiator tubes (means you need a new radiator), or a head gasket leak (not good). Let me know what you think.
 
YOU SHOULD NEVER MIX COOLANT TYPES !!!:eek:

Regular green colored coolant has Ethylene Glycol, which IS NOT COMPATIBLE with DexCool, as they turn into gel when combined, which clogs your radiator and other related parts.

I HIGHLY DOUBT THAT YOU CAN DO A SUCCESSFUL FLUSH AT THIS POINT, without replacing a few parts first.

First you should replace the radiator and thermostat.
Next do a old-fashioned Prestone Super radiator flush (NOT A PRESSURIZED ONE AT BRAKE MASTERS), since the gel may end up clogging up more stuff. Follow the directions on the bottle.

Hope for the best :)
 
Oh, and don't forget to dilute the new DexCool with De-mineralized water (50%/50%) or just buy the premixed jug.

You should do the flush with the 50%/50% mix as well. I know this will cost more, but you absolutely do not want anything else inside your system.
 
california roofer said:
YOU SHOULD NEVER MIX COOLANT TYPES !!!:eek:

Regular green colored coolant has Ethylene Glycol, which IS NOT COMPATIBLE with DexCool, as they turn into gel when combined, which clogs your radiator and other related parts.

I HIGHLY DOUBT THAT YOU CAN DO A SUCCESSFUL FLUSH AT THIS POINT, without replacing a few parts first.

First you should replace the radiator and thermostat.
Next do a old-fashioned Prestone Super radiator flush (NOT A PRESSURIZED ONE AT BRAKE MASTERS), since the gel may end up clogging up more stuff. Follow the directions on the bottle.

Hope for the best :)
Click to expand...

The fluids were never mixed. It was completely flushed of the dexcool then conventional has been used ever since
 
What about the water pump? Are you absolutely sure it is not stuck?

Do you have a "Service-Engine-Soon" light come on? If so, then retrieve the code and replace/repair whatever is causing the malfunction.

Engines do not just overheat for no reason, even if they're getting older. Something is causing the engine to overheat. Weather it is a faulty sensor not doing it's job, which dominoes the rest of the system to malfunction, or if it is a faulty "hard part".

As Dirtclod mentioned above "do you trust your temp guage?"

It may even be a leaking vaccuum tube.
 
OK, I'm old & slow. Something just came to mind. The exact same symptoms in a work truck. Turned out to be the fan clutch. It was slipping and wasn't able to pull enough air under load. Just like a slipping fan belt.

To test: cold engine, ignition off, try to rotate the fan. It should turn, but it should be very difficult to turn. Sometimes there is evidence of fluid leakage on the ribbed aluminum of the fan clutch.
 
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Well after taking it in Monday all fans, water pump, thermostat, checked out fine and the mechanic couldn't get it to overheat during 3 test drives with AC on. The scan tool temp matched the gauge temp of 190. Outside temp was 70

Today it overheated again took it in the scan tool temp was 225 that matched the gauge again. The mechanic now wants to replace the radiator. He says he could have it checked out $80 but he thinks it's bad. He says if the coolant drains clean the radiator is probably shot. If it drains dirty he will flush and reevaluate.
 
second the fan clutch. My 2003 tahoe ac wouldnt work at all in town and ran hotter than normal on the hwy worked some. The outdoor temps were a bit higher 100+
 
Guys I am having the same problem with my 2003 Sierra 1500HD. I changed the therostat and the coolant reservoir with a new coolant sensor and drained the old Dexcool but I didn't flush the radiator. I added new Prestone antifreeze and it won't take more than a gallon and still runs hot very quickly.
 
LarryLive said:
Guys I am having the same problem with my 2003 Sierra 1500HD. I changed the therostat and the coolant reservoir with a new coolant sensor and drained the old Dexcool but I didn't flush the radiator. I added new Prestone antifreeze and it won't take more than a gallon and still runs hot very quickly.
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If you switch from dexcool to a conventional antifreeze you need to flush the whole cooling system first. Dexcool and conventional antifreeze will turn to a sludge or gooey substance.

How long has it been since you mixed the two products?
 
Complete Flush and Fill

Took the truck up and had a complete flush and fill performed and it seemed to take care of it. The tech said he couldn't find any trace of the Dexcool left anywhere in the system so there was no gel in the system. Refilled with regular antie freeze and it seems fine now and runs at 190 degrees
 
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