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My 2008 2.7L with about 140k miles that has been having an overheat issue. I've been working on this for a couple weeks and have not found the solution yet.
It overheated 3 times, and each time the expansion tank is low to empty. On the 3rd time, I topped off the tank and my wife drove it home (about 10 miles) and it overheated again. Checked the tank and it was still full, maybe dropped 1 inch. She reported that when it overheated, she turned on the heater and it blew out cold air, then the air got hot and the temp gauge dropped to normal. It does not overheat all he time, I've driven it several times with no issue. I often see signs of liquid that has come out of the over-pressure hose at the cap. Why does this not go to an overflow tank like they used to? It just dumps to the ground.
Here is what I have done: No external leaks except from over pressure at cap. Replaced thermostat, replaced radiator cap, dumped coolant and added new, pressure check system- OK, oil looks ok and level not high. Temp on upper hose is 180-200, lower hose 150-160 when engine is at temp and normal so radiator seems OK. Hoses feel stiff when hot.
Questions: Is regular 50/50 ethylene glycol green coolant ok for this car or does it require something special? How can I test for flow to see if my water pump is pumping normal? I really don't want to change that unless I have to. I've seen comments that some engines have two thermostats. Do I have 1 or 2?
Sorry for the long post, but wanted to give as much detail as I could. Thanks for reading.
 

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What a boiling over situation you've got brewing! the T-stat is supposed to set in a certain position for the bleeder port to function properly, also careful bleeding of trapped air pockets must be done. "Regular" "green" antifreeze is okay to use, but you will not have the "long life" additives that came as original. Check that the radiator fins and A/C condenser fins are not plugged up with bugs or debris, as that can cause a major loss of cooling efficiency to the whole system.
 

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It sounds to me that you have trapped air in the cooling system. Years ago, I had a Concorde that had similar symptoms. I would go just a few miles and the temp gauge would shoot up to high, then it would come back down, go back up, etc. On that engine (V6), there was a bleeder valve on the upper radiator hose housing (where the thermostat is located). After several tries at bleeding the cooling system (opening the valve with a hose attached until the air was all out), it finally settled down and everything was OK.

I don't know if your engine has a bleed valve or not (if it does, it's most likely on the radiator hose housing where the thermostat is located). If it does, find a small hose that will fit over the valve's nipple. Let the engine get up to temperature, then open the valve a little until coolant begins to come out of the hose. Put the end of the hose into a pail or something to capture the coolant. You may want to "rev" the engine every now and then to speed up the process. When an air bubble reaches the valve, the coolant will stop flowing from the hose. Once you get a steady stream of coolant (no more air bubbles), tighten the valve and try the car. Oh, one more thing. Be sure to keep the coolant recovery tank full of coolant while doing this. If it gets empty, it will suck in more air.

If you don't have a bleed valve, open the radiator cap and run the engine. Trapped air will eventually escape through the open radiator cap. This method will take longer, and you don't know if/when you've got all the trapped air out, as you can't see any change in the radiator like you can with the hose.

Good luck!!
 

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WELL said "team mate", I had just got in from Celebrations when I replied early this am! Nice explanation. Totally agree about the "bleeding" process,my 98 2.5 coupe is the same for being a monster in the cooling system air pocket problem also. It has an "overflow" tank, but only holds about a quart of coolant O. E., so must be VERY careful when doing cooling system work!
 

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it does have a bleeder valve right on top of the t-stat housing try bleeding that also turn your temp control all the way to hot but your blower fan off and wait for your cooling fans to turn on if they dont it might be your cooling fans or even something to do with the sensor
 

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Discussion Starter #6
Thanks for all the input. I do have a bleeder valve where the upper radiator hose connects to the engine. It looks like a thermostat housing, but on this one, the thermostat is on the lower hose. I know since I already replaced it. One of the other motors has 2 thermostats.
As it turns out, my problem is the head gasket is leaking combustion into the coolant. I did the coolant combustion test where you pull fumes from the radiator tank to a test kit with a chemical inside and the chemical changes color. I did to a pressure test earlier and it passed. After doing some research, I learned that the pressure test is a test for a gross leak and you can only test it up to around 15-16 psi. Pressure in the cylinder is much greater, which is why it can leak through and the pressure test passes.
I debated using some stop leak as a quick fix, but after some research, decided not to. Having a shop do the head gasket job and will replace water and oil pump while they are in there. This is my daughters car, and she needs something she can depend on when she goes back to school in the fall.
 

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Well ,that (bad head gasket) would definitely cause the same symptoms you posted, just the worst case scenario of it.
Hope all works out well. And good luck for daughter in school. Mine is doing her Masters.
 

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My 2008 2.7L with about 140k miles that has been having an overheat issue. I've been working on this for a couple weeks and have not found the solution yet.
It overheated 3 times, and each time the expansion tank is low to empty. On the 3rd time, I topped off the tank and my wife drove it home (about 10 miles) and it overheated again. Checked the tank and it was still full, maybe dropped 1 inch. She reported that when it overheated, she turned on the heater and it blew out cold air, then the air got hot and the temp gauge dropped to normal. It does not overheat all he time, I've driven it several times with no issue. I often see signs of liquid that has come out of the over-pressure hose at the cap. Why does this not go to an overflow tank like they used to? It just dumps to the ground.
Here is what I have done: No external leaks except from over pressure at cap. Replaced thermostat, replaced radiator cap, dumped coolant and added new, pressure check system- OK, oil looks ok and level not high. Temp on upper hose is 180-200, lower hose 150-160 when engine is at temp and normal so radiator seems OK. Hoses feel stiff when hot.
Questions: Is regular 50/50 ethylene glycol green coolant ok for this car or does it require something special? How can I test for flow to see if my water pump is pumping normal? I really don't want to change that unless I have to. I've seen comments that some engines have two thermostats. Do I have 1 or 2?
Sorry for the long post, but wanted to give as much detail as I could. Thanks for reading.
If you have a burp valve on the thermostat housing try to burp it if not my be head gaskets I just had to do this to my 2014
 
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