Changed heat sensor, radiator cap, thermostat. Fans working. Ran without thermostat and temp went to normal or cooler. Put thermostat back & started overheating again, bled system properly. Radiator shop ran chemical test & said barely showing, but could be head gasket or crack but not definite. No exhaust smell or steam, no oil contamination. Drove car in overdrive at 1200 to 1500 rpm & when it gets to 3/4 hot, stopped & put in low gear & ran hard for 1/8 mile, temp comes down to normal. Repeated and same results. When idling car in garage and it got hot over half, revved motor & held at 2800 rpm & temp comes down to normal. Have not run any flush through system and haven't done anything with water pump.

 

heads are warped

 

"Lucy, you got some splainin' to do"

Not that I'm doubting you, but what brings you to that conclusion so quickly? I have a very similar problem and have convinced myself that I am not getting the air out of the system properly.

 

radiator cap, thermostat. Fans working basics are checked

Drove car in overdrive at 1200 to 1500 rpm & when it gets to 3/4 hot, stopped & put in low gear & ran hard for 1/8 mile, temp comes down to normal.

while driving the engine makes more heat and it will over power the radiator and also if he puts a funnel on the radiator cap and U rev it up U will see bubbles come out. thus the heads are warped enough when it gets hot past 215 the head gasket wont seal it any more and it pushes out the coolant in the system and over heats U let it sit and the radiator can cool it back off. Common for 3.5 motor when the coolant has not been changed as well as the engine over heated to many times.

I am currently doing this sorta job for one of my customers.

 

Makes sense, but wouldn't you get a loss of coolant under that scenario?

If the system did have air in it, would it act the same or would there be different symptoms? I'm piggy backing Dank's thread here, but as I said, I am having a similar problem as he describes. I did a compression test and had 145-150 psi in all cylinders. That coupled with no visible contamination in the oil had me convinced that the head gaskets were good. I can understand what you are saying about the head gasket losing their seal under heat, but I don't understand it sealing back up on cool down.

 

The first time this happened the temperature warning light came on and the car was cooled down quickly and hasn't been run to that point again. I am currently running flush through system and will see what results are after that. Trying to make sure it's not any other reason besides warped heads. If you have any other info please post. Thanks.

 

When you are refillng system, are you filling to the top of the recovery tank or are you letting it drain down the the min/max water level marks?

 

Heads problems can manifest themselves in many ways. In recent years Chrysler has went to the multi-later steel head gaskets. There is no such thing as "blowing a head gasket" anymore. The steel is not going to push out or rot out over time like the old school pressed materials. If the engine gets hot past a certain point...it's head time. Both sides usually.

 

I use a funnel on the coolant bottle fill it up run the engine and watch for the bubbles to burp out when the temp is high.

 

there's a bleed valve for that, but the air bubble burping is still an option since that's the desired result. I think the bleed valve get's the air out quicker.
I have also seen the water pump impellar come loose from the shaft. More prevelant on some gm pumps, but still could be. What happens when it does this is it turns under serious demand but does not under normal load. So at 1200/1500 rpm, probably more like a normal load. "running hard for 1/8 mile in low gear"? That tells me 3K ish and would probably turn enough to pump fluid, thus cooling down. Just a thought.
Also, did your radiator guys "pressure test" the system? That could tell you things you didn't know before.