I've got a combination of engine cooling issues working to confuse me. The vehicle: '02 4WD 3.0L with 85k miles. I'm prepping it to gift to wife's sis, and while the cooling system has never given a lick of trouble I just completed a complete flush and fill with new thermostat (original 192* type) because the coolant hasn't been changed in ~8years.

For background, the gauge NEVER goes beyond halfway between C and H marks, and there's never been an indication of overheating from overflowing reservoir or knocking. As always the gauge just goes to half and sets there, but while using a reader to monitor operation during the refill and bleeding I noticed the reader showed 160* when the gauge gets to the halfway point and stopped, but the temp showed it clearly continued to rise up to and past the 192* point where the TS is supposed to open. Also, at no point did either of the fans ever come on, even as it approached 215* where I shut it down. I watched the temp on the reader gradually cooled and the dash gauge finally also starting going down at 160* just as expected.

While running hot I turned on the AC and at least one fan came on immediately as expected. So, with all that I'm left to wonder if it's just expected for the fans to come on only above the temp I got it to.

I've seen one online blog-type post that this engine turns the fan on at 235*, but checking additional (hard to track down) confirmation as that sounds rather way too hot. Any leads or differing specs?

There's the added feature now of fixing the obviously 'not working right' dash gauge that's topping out at 1/2.

 

Hi , i got a 2003 and never seen it go past 1/2 over the 5 or 6 years owned even when idling long time and the fans came on (no ac on and in +40c days) , i heard a story that these temp gauges are a on / off type of thing not linear like in the old days , story went like a dude was driving along slowly in the city and thought he could smell a hot engine and thought he saw a slight whiff of water vapor/steam from under the hood , looked at temp gauge and it was ok (still a half) 2 to 5 minutes later the engine started missing and more smell and vapor looked at gauge again and it was full hot , that's all i got but if the gauge is set at half and no overheating alls good imo , he also fitted a dash OBD display those cheap ones that reflect off the windscreen after that episode , me? if it stays normal i'm good with it imo , good luck .

 

Well, update. After the info above from yesterday and then getting out this morn. I first noticed the reservoir had lowered overnight from 2" above the Max Hot line (aka the seam) to just an inch above it. So, at least some contraction and maybe a tiny bit of bleeding. I added another inch again, and this time put the cap on tight. With my reader everything the same as yesterday as far as idling after start:
120 just starts to move off the bottom fat bar
130 hits the C bar
140 is 1/8" from halfway
160 is 1/2, and then it sits there motionless as the scanner needle keeps moving all the way to 200 !?!?

Scanner was at 190 for one minute solid, but no detonation, clatter or smells just smooth idle.
After that it moves to 200 and that's when I hear something new and sure enough both fans are on.

With the gauge still at 1/2 the scanner shows steady at just a hair over 200, and hitting the pedal there's no ping or chortle. I turn on the AC and it blows fine and the temp lowers to ~195, and then slowly back to just under the 200.

I just recently did all new brakes so I took it out for a spirited drive to bed the pads/shoes while watching the temp. Nothing out of the ordinary - everything normal. So, after I've read newer motors like to run hotter than the old days, it was like you say and for all these years it's been running fine even so close to 'Hot', but with the gauge lying about it the whole time.

 

Good on the car and all that stuff interesting info btw , one can hopefully feel a bit more relaxed now , take a peek at those OBD display things (i don't use one even though they be cheap on the Bay atm) , some are setup to reflect off the windscreen and some one just looks at the separate display if one needs a bit more comfort as they display what the scanner says not the OEM Gauge , and LoL imo it doesn't Lie , it just Fibs a Bit , some Lawyer or Politician must have designed it !