[fyrffytr1]

My son's 06 Chevrolet 1500 pick up truck started overheating while stuck in bumper to bumper traffic on I-75 south today. Air temp was upper 40s-low 50s.
Once he got out of the traffic jam the truck ran fine.
But, when he got here it happened again. Within the last year we have replaced the water pump, thermostat and both radiator hoses. Electric fan is working and cycles on and off.
He said the temp gauge will go up and down from normal to the hot side and coolant is being forced out of the over flow tank.
Could it be a bad thermostat or what do I need to look at?

[67drake]

Does he still have the stock shroud in place?
I don’t think it’s as big an issue these days, but has the block ever been drained and flushed?
Might be worth using one of those laser thermometers too, to compare the temperature at the inlet and outlet of the radiator. I believe it should drop at least 20 degrees.

[fyrffytr1]

Stock shroud is in place. I will check the temperatures tomorrow. The way he explained it to me, the temp gauge needle was going up and down as he drove.

[dataway]

How many miles on it?
Original radiator?

Usually those cooling systems are pretty bullet proof.

[mgarblik]

Those vehicles can be very difficult to get the air out of. A failed head gasket is also a possibility but hopefully not in your case. To try and purge the air, I would try the following: Jack the front of the vehicle up so the radiator is the highest point in the cooling system. Try to wedge the gas pedal with a long screwdriver or stick or something to get the engine to run about 1500-1800 RPM steady. Let engine run for up to an hour in this scenario. That should purge the air through the surge tank with the lid off.

If that does not work, next I would have a combustion gas test done on the cooling system. Any shop worth a damn can do this. You put a tool with blue chemical in the radiator opening or surge tank. With engine fully up to temp, the blue chemical will turn yellow/clear if combustion gas is in the coolant. It is a quick, 10 minute test. That should give you lots of information.

When I had my fleet business, we had so much trouble with Chevy/GMC trucks doing this nonsense, I bought a vacuum filling system which pulls a vacuum on the entire cooling system. This allows you to fill the system without air getting in . Most likely, air in the system is the issue.

Finally, don't overlook the possibility of a defective cap causing this condition as well. Best of luck with it.

[fyrffytr1]

Originally Posted by dataway

How many miles on it?
Original radiator?

Usually those cooling systems are pretty bullet proof.

140,000 miles on the original radiator. Had the head gaskets replaced about 8 years ago.
This is an intermittent issue. Truck ran fine this morning when he came over to my house, but after leaving here the needle started surging.
He just came back and reported that the needle jumped one time but has since been running good.
What if I put a back flushing tee in the upper heater hose and took the cap off until coolant flowed.

[mgarblik]

Does that model truck have a radiator cap where you can look inside at the tubes? If yes, are they clogged-up looking? The intermittent nature of the problem also leads me to believe you could be looking at another set of head gaskets. I would do the chemical dye test for piece of mind. As good as the LS series engines are, the light weight, aluminum heads and wide spaced 10 head bolt layout has not been great. Head gasket failures are pretty common.

[Formulabruce]

DEX COOL. do a very thorough flush. When refilling put front up on ramps. Bleed air top hose at radiator. Dex cool gets old and can clog up a radiator. Even if you change fluid 15 years later.

[fyrffytr1]

Originally Posted by Formulabruce

DEX COOL. do a very thorough flush. When refilling put front up on ramps. Bleed air top hose at radiator. Dex cool gets old and can clog up a radiator. Even if you change fluid 15 years later.

Replaced the water pump, both hoses and thermostat two years ago. Drained, flushed and refilled the cooling system. We did not use DexCool coolant. O'reilly store brand universal.

The truck has been running fine since he left here going back to north Ga. on New Years day.

[salem1912]

You say the fans are cycling on/off. Next time fan is on see if it is drawing warm/hot air or if it is cool to your hand.. If cool you have air trapped in the system.

[OCMDGTO]

Originally Posted by dataway

How many miles on it?
Original radiator?

Usually those cooling systems are pretty bullet proof.

The radiator in my 05 2500 started leaking through the plastic tanks many years ago

[FrankieT/A]

Aftermarket thermostats have been problematic these days. Even Stant have had issues, I would look at that.