Upper Rad hose pressure
 

Hey guys, I am back again. This time I am having an issue with my upper radiator hose building up pressure and blowing it off from the radiator. I went the easy route and changed out the thermostat thinking it would work. It didn't. My next thought process would be to change out the radiator because it may be clogged. Or change out the radiator cap. Anyone have this issue before? It my '05 Pacifica with the 3.5L V6.

The radiator cap is designed to to be pressure regulating, it should be be dumping radiator pressure should it go over ~14 psig. If in doubt, change it, they are not expensive.

The factory dash mounted engine temp gauge is not to be trusted, if you have a OBDII scanner (or can borrow one from the local auto parts store) you can obtain a more accurate estimate of operating engine temp. My own is always in the range of 205-207 deg F, depending on weather.

My engine temp gauge will not read hot until the rad hose pops off. Yesterday when I checked the upper hose it was really firm, so I decided to check the lower hose and I was able to squeeze it with almost no effort which lead me to believe there was a blockage in the radiator! My boss has the red laser thermal gun that I could borrow from him to check the temp of the engine with. For ****s and giggles I might as well replace the cap since I have no idea how long ago it was replaced and go from there!

When you replace the coolant, are you bleeding the air from the cooling system?
The 3.5 liter has a bleeder valve on the top of the engine so that trapped air can be removed from the system.

Bili! Yes I have bled the air out. Even after doing that, the upper hose still builds up pressure.

Look for bubbles in your coolant, it could be a head gasket.
That can happen when a head gasket fails.
Just pull the cap while the engine is still cold and start it up.
If you start seeing bubbles, you now know where to look.

If it was the head gasket, wouldn't I get coolant in my oil as well?

Not if the leak is between a coolant passage way and one of the exhaust ports. Just a pin hole would do it.
It does not have to be much of a leak for compressed exhaust gases to be forced into the coolant passages.

Also, if the thermostat is put in backwards, it will not open.
I have heard of people doing that with the 3.5 liter engines.

I noticed that the fan on the driver side of the shroud does not kick on right away! Are they both supposed to kick on at the same time or are they independent from one another? I have to tap the fan for it to even kick on. Would that be part of the pressure build up issue?

It should not be, one fan should only come on when the temperature hits a certain point, or in some cases when you turn the A/C on.

The coolant fans on Pacifica's are wired in parallel. They should kick on/off and run at the same speed (they are variable speed), if they don't it is time to R&R. I have gone thru quite a few failed electric fan motors, never had any blow the radiator hose off..

Sharing almost situation as pressure is building up on the coolant reservoir. I thought it was the thermostat. It turned out to be the driver side fan intermittently kicks in and/or if it kicks in, the RPM is not enough. It turned out that the fan motor is at fault already and I just changed it. Now cooling system is back to normal.