I have this problem posted in YT in several places but I'm still trying to figure out what the problem is if there is any.
I have a strange problem with my 02 sebring 2.7. The overflow tank never gets pressurized. I've replace the original cap with a pressure relief lever cap and it still does not pressurize. Fortunately , there isn't any cooling issues. No loss of fluid, no leaks, fluid looks great. The interior gets heat. the temp gauge is two ticks up from cold during normal temps after warmup max. Same when it's cold out. It takes about 15 minutes to start warming up the interior on a cold day. When it hot it's almost at midway. I'm not sure why there is no pressure.



So, there may be an issue with it not pressurizing and the TS might be stuck open. Maybe the new cap or the tank might have a leak stopping pressurization. I've looked at the cap stem and don't see anything.



Q- will this lack of cap pressure stop circulation through the engine? I don't see any movement in the tank just a little warm evaporation when i take off the cap. The tank does get very warm just like the hoses around it after running. When the car is not running, the expansion tank is at the full MAX line. When the car is running and warmed up the fluid in the tank raises a couple of inches. It goes back down when it's cool. Again, the coolant looks clear green in this case and does not lose any fluid. I haven't put fluid in this in at least a couple of years. There aren't any whitish staining anywhere.The water pump was replaced 30k miles ago. I'm assuming that if the pump was failing or slightly failing, the engine would be overheating. Does that make sense?So maybe just to see I could replace the expansion tank and change the thermostat to see if that works.

 

I wonder if somebody put straight anti-freeze (not fifty-fifty mix with water) in the system?

Might want to have that pressure cap tested to see if it's really holding. With the expansion you noted there should be some pressure in there even if there's no water.

The antifreeze is supposed to be golden in color. Check your owners manual for the correct antifreeze.

When a water pump fails, it leaks. It'll still pump water.

If the car is not overheating or running too cold, the t-stat is probably okay.

Any issues with the temp when the A/C is running?

How about fan operation? The fans are controlled by the computer and are not supposed to be running at all times. With what you describe, they may not come on much. They both don't come on at the same time. If they are both running all the time, that's not right.

 

so I so I got up today and the goal was to Simply turn the car on. Turn on the air conditioner keep the hood closed and let it run idling in the driveway at 60 degrees outside temp and see what it does. I'd replace the vented cap with another one from AutoZone.

So what I found after letting it run continuously the Overflow pressure tank expansion tank is holding pressure now. So after replacing the original cap with that pressurized lever cap it did not work correctly. The second one finally worked and it's getting pressure. It's really not a whole lot but it's definitely noticeable as I opened it the water level Rose about 1 inch. so I guess it's all good I'm keeping an eye on it as it's been running for a three or four hours in the driveway.

The temp gauge is holding about two ticks from cold. The heat is blasting in the interior. And the AC is on and everything seems to be holding thanks again for the help. So I'm still working with the concept also that the thermostat might be stuck open. Again is I had mentioned that the heat takes a while to get warm air out of the dash and for the twin cooling fans to kick on. At least 20 minutes with an idling in the driveway before the fans kick in. Takes about 15 minutes of driving on cold days for the heat to start coming out. But as everyone agrees this is the best scenario is being stuck open and not stuck closed. So I'll work on that in the next couple of weeks. I can just pop it a new thermostat as it's right on the top of the engine.