04 Edge 2wd 3.0 with 138K. Did comprehensive cooling system service few months ago, timing cover leak, w-pump, hoses, t-stat, radiator with cap.
Prior to that had replaced heater valve when it failed a while ago.
All was good not leaks, temperature gage centered in dial.
Fast forward to this morning driving to work about 9 miles temperature gage never got up much past the first lines.
Outside temp was in mid-to high 20's. Driving home temperature went up a bit more but not to where it normally resides.
Any thoughts on what to rip into first? New stat stuck open?
As side note, around thanksgiving family member locked themselves out of truck with the truck running and it was 40 minutes before we got a spare key to unlock. Temp gage was dead middle all the way thru.

 

Yes, most likely new t-stat is leaking coolant out to radiator

You can check it by starting engine cold and then popping the hood
Upper rad hose will of course be cold and so will heater hoses

After 2 or 3 minutes feel then again
heater hoses should be warmer now and upper rad hose still stone cold

If upper rad hose is warming up the t-stat is allowing coolant to flow to rad, and it shouldn't

Radiator is there to bleed off EXTRA heat, t-stat is set for 190-195degF so when coolant in engine and heater get to that temp t-stat starts to open and send EXTRA heat to radiator


One other thing can happen although not common, fan clutch can lock up full time
The cold air it pulls in to engine bay all the time can cause cooler running temp

Before starting cold engine, pop the hood, try to spin the fan, it should be locked, can't spin it and should barely turn
Start engine let it run for 30second and shut it off
Fan should now spin or at least move much easier, it's unlocked
Fan clutch is engaged/locked by radiator heat, as the center of the radiator gets warm the fan clutch starts to engage, the warmer rad gets the more it locks, spins closer to water pump RPMs

When engine has been off for a few hours the oil in the fan clutch will cause it to lock again, once engine is restarted the oil will flow again unlocking the fan

 

Thank you Ron- I will do those checks in the morning. After driving home this afternoon about 10 miles the upper radiator hose was warm but not hot, if that is an indication of anything.
Almost wish it was the fan so I would not have to break into the cooling system!

 

so this morning did the checks: engine was cold ( sat overnight) and radiator fan turned easily by hand. Started the engine and let it idle for several minutes. After about 4-5 minutes the heater hoses where clearly warming up but the upper radiator hose did not warm up with the heater hoses.
The fan kept cycling on and off, that roaring sound you hear when you take off, came and went away in cycles.
Any thoughts?

 

Can't say what might be the problem

In the old days in cold climates, under 32degF in the day time, we had to put cardboard in front of radiator to get engine bay and engine to stay warm enough for heater to work
You've seen the snap on or zippered Grill Covers used on semi-trucks in cold areas, same thing applies to any other engines, if they can't generate enough heat in low air temp environments

 

yeah I am old enough to know about the cardboard trick, only semi driving folks do that anymore. I will change out the fan clutch and thermostat, probably will buy motorcraft stat, it cant cost that much.

 

If the upper rad hose didn't warm up like heater hoses then thermostat is working, blocking flow to radiator until coolant temp hits 190degF

 

Went ahead and changed out the fan clutch. Got Hayden brand on-line, the new unit has a catchy spot when you turned it hand, also the hex was much bigger than stock making already tight installation even tighter.
Put it on regardless and it did not fix the issue. Temperature went midway up during 2 mile test drive at 45 degree weather. Heater puts out fairly hot heat. We will see once it turns colder again.
Could it be temperature sending unit? Could be bad gage also.

 

If heater was hot when gauge should cold then yes, could be sender or gauge issue, but if heater gets colder then sender and gauge are working fine

 

ok did follow up this morning with outside temperature around 30 degrees. Took temperature readings of the heater hoses and upper radiator hose with a cheap radioshack instrument.
As the engine was warming up the upper radiator hose was reading about 8-10 degrees cooler than heater hoses, 50 and 59, 70 and 78. Temperature gage never moved yet.
Looks like I am going to replace the new stat and see what happens, easy job but need to wait for a warmer day.