2010 Overheating

[2010 Expedition]

I haven't seen this before. Wife said it was running hot, then would cool, then would peg hot, then would cool.

I diagnosed as a stuck Tstat. Bought a new one this morning, put both in a pot of water, old one never opened (even at 210*), new one opened at 195* as it should. Put some more coolant in it to the "cool fill level." Drove it this afternoon approximately 20mi round trip, both on highway and in stop and go.

It would overheat, show a light on dash, cool, peg hot, cool, peg hot while driving, then when I would pull over and stop, it would immediately cool to below 50%, then when I pulled back out to limp home, it would peg hot again.

Top hose - hot as hell
Reservoir - still full at "cool fill level"
Bottom hose - not as hot as top
No visible leaks
Tstat - new as of 0800 this morning
Both primary and secondary fans running

Possibilities:
Water pump
clogged or bad radiator

 

[stamp11127]

Welcome to the site. Did you burp the system? If you have temp gun see what the temps are on the radiator hoses. Also check for fan clutch operation.

 

[2010 Expedition]

Thanks for the welcome. No, I don't have a temp gun.

How would I burp the system? Is there a air vent valve? Leave the cap off?

Also, in looking this thing over, there doesn't seem to be any hose (other than the overflow) coming off the reservoir. I put coolant in it this morning, but only in the reservoir. How does the system get fluid OUT of the reservoir?

 

[stamp11127]

Probably a line connected to the bottom of the tank. To burp the system I usually park on an incline so that the surge tank is the highest point of the system. Bring engine up to temp while squeezing the upper rad hose. Have the heat on also.