Truck's been acting weird over the past week or so.

A month or two ago, I replaced the old leaky brass radiator with a Champion aluminum radiator. Refilled it, got all the air worked out, and have been daily driving the truck since, and it's done great. Been running the AC every afternoon and no overheating issues at all. Temperature needle has been staying about in the middle of normal.

I drove it to my mom's last weekend, up a 2 or 3-mile 8% grade. Outside temp probably under 80. Unloaded, just me and the kiddo in the truck, and doing 65-70 MPH in 3rd, overdrive off.

I had been keeping an eye on the temperature gauge, watching it climb. It was above the L in normal, and it nearly hit the red by the top of the hill. Then my kid asked if my "ENGINE TEMP" light should be on ... oh crap.

Immediately dropped my speed and limped it to the top of the hill, but the dang thing just would not cool off even after cresting the hill. I pulled over and could hear it boiling in the upper radiator hose, and the overflow tank was full to the brim.

The engine itself didn't feel unusually hot, though. The hood wasn't either.

It cooled down after being off for 15 minutes or so, and then acted relatively normal.

Well, actually, not normal. Now it doesn't want to warm up. It runs really cool for a long time -- takes 20-30 minutes for the needle to even get into the "normal" range. But it hasn't overheated since. Before it overheated, it would get to "normal" within 5 minutes of driving, consistently.

Any idea what's going on here? Did I fry something, like maybe my thermostat? I'm wondering if it's stuck open now, which is why the engine's running cool.

I've got a replacement Motorcraft thermostat in a box. I'm thinking maybe it's time for me to do this job.

 

sounds like the thermostat stuck.

 

Yeah, I'd start with the thermostat.

Mike

 

Yarp, would say your thermostat stuck open. ive been having some weird cooling issues myself, pretty sure my radiator is plugged up inside. Bottom tank is just as hot as the top, hell couple days ago it boild over on me too... just got back with the trailer, sitting in the driveway idling after about 20 seconds of the temp slowly dropping it just started boiling over.... never seen anything like it, was in the middle of the gauge, it gets to L fairly often if ive got a load on, but not over and had never boiled before.

 

Looks like one of my evenings this week just got booked. Thank you, guys.

 

I've replaced my radiator about 3 times in the last couple of years. Twice because of leaking radiators the last time thanks to a deer at 5am. What should the temp be reading running down the road and when running around town after running about 60 mph for 20 miles? My temp gage, not the piece of junk original but an after market real gage will run about 180/190 till I get to town then if I stop like going thru a drive thru, it'll get upto 205 but after running thru town it'll go back to 190. What is the highest I want to see?

 

I would think that is pretty normal. Sitting at a stop light or in a drive thru, your relying on the fan only to move enough air to cool the engine. In warm weather, temp will rise some, especially since your fan clutch won't kick in at that low a temp.

 

i've replaced my radiator twice in the last couple years. first one because the original was corroded badly and leaking in several places, second one because the plastic tank separated from the aluminum core, and the current one is all aluminum and is working great so far.
temps are normally 195 or so, i have e-fans on mine, first one kicks in at 210, second one is set to kick on at 230 but hasn't come on since i got the lower temp one set up.
its considered perfectly ok to run these at 230 when they're working hard, but too much hotter starts to get scary

 

190 is when the t-stat opens, 215 is fully open. Dont go over 240

 

Keep in mind that temps can vary by a few degrees depending on where you have the sensor installed. The two most common locations are in place of the factory sensor and in place of the factory overtemp sensor (the one for the dummy light). I put mine in the latter location. With a brand new Motorcraft thermostat, I'm seeing it get to 200, then it opens up and sits between 190 and 200, but goes over occasionally if I get silly with it. This is unloaded. Haven't put a load on it since in installing a new thermostat. The old (original) thermostat would keep the engine a good 10-15 degrees higher and would have me into the 230s with fairly light loads, but hopefully the new thermostat fixes that.

Mike

 

Well, I replaced the thermostat this weekend:



I wish I had known how (relatively) easy of a job that is; I wouldn't have waited so long to do it.

The old thermostat was one of those MotoRad "fail safe" thermostats, and it was indeed stuck open.

I replaced it with a genuine Motorcraft, I forget the part number but it was the one you're supposed to use on IDIs.

I also removed the little brass check ball from the gooseneck on the advice of some other forums.

Drove around all day yesterday, did several hard uphills in the Manzano mountains, and the truck is back to normal (temperature never got above halfway between M and A). Once I crested a hill and let off the go-pedal, it dropped immediately rather than staying where it was.

Looks good! Thanks for the advice guys.