Hi guys, I'm new here and I hope you can help me with my 2001 4.6L. Yesterday after driving about a hour at Interstate speed, I noticed the AC was not cold. Then the oil/temp combo light came on. The temp gage was in the red. It was extremely hot outside. I pulled off, turn the engine off and looked under the hood. No steam or coolant coming out anywhere. The plastic reservoir had coolant within the cold fill range. In short, no physical signs of overheating.

I started the engine within couple of minutes and the gauge was about half way with no light. Started driving and within a few miles same thing again. Same solution. I finally slowed down a bit a got where I was going. Coming back I figured out that if I didn't run AC, the temp gauge would stay in the safe zone.

Today I drove it to work about 20 miles with AC on. No problems. Same thing on way back.

I'm thinking a sensor problem, but I don't know anything about them.

 

is your truck full of coolant??

 

Yes, the plastic fill tank is about half full, well within the cold fill range.

I haven't looked in the radiator, and frankly don't know how with all the plastic around it.

I don't think the engine is really getting too hot. Once they get hot, don't they stay hot for a while?

 

It could be your thermostat is not opening all the way, or your rad cap is not getting the system to the required pressure. If you never change your coolant that could be an issue. Your water pump impellors could be worn right off and not allowing your coolant to circulate properly. Your rad could also be plugged or just toasted due to age and miles.

 

I had the same exact problem, I checked the thermostat (super easy to check/fix) I checked the radiator cap and everything looked goof. I spend a lot of time in the mud and dirt so last I checked the radiator fins and they were caked with crap and not letting any air through. I just took a water hose and sprayed it out good and it fixed that right up.

Just a thought.

 

I put in a new thermostat myself this winter to get rid of P125 codes. Of course I lost a little bit of coolant in the process. I replaced it with some old coolant I had and just guessed my 50/50 by pouring in some coolant and then water. Maybe the coolant is shot or my mix is not close enough?

I got a flush and fill last fall. I did get stuck a few months ago, so dirt could be an issue.

No problems with it today. Not sure if I can reproduce it unless I drive hard for sixty miles or so. How could the truck be cool enough instantly by shutting it off and immediately restarting?

 

the mix doesnt matter, I run straight water with 2 small bottles of Water Wetter through my cooling system until its winter time, then go with antifreeze.

 

I haven't had any problems since that one day. The radiator is not clogged with dirt.

If the water pump impellors were worn out, wouldn't the truck get hot pretty quickly? And stay hot?

I'm tempted to forget it and just keep on driving.

 

Is it running rough at all? I know you said that it was at the cold fill area, but that is when it was hot, is it that way when it is cold? Is the leavel differnt at all from cold to hot?

 

Heard of another guy with the same problem, turned out being the ECT sensor in the head , I think. His truck wasn't really hot but was showing hot and the oil and temp lights came on. If that sensor is bad it will make the a/c not cool also. It isn't the one that goes to the gauge-it goes to the PCM.

Might try a search because I'm not certian it was called ECT (engine coolant temp) could have been cylinder head temp sensor.

But it does sound like a dead ringer for the symptoms you have. Maybe somebody smarter than me can chime in.

Good luck and post the fix.

 

The truck is running great. The water level doesn't seem to change much at all. I'm thinking jgger might be on the right track.

 

cant you depressurize the system and stick a thermometer into the overflow tank to see if the water actually is cooking?

 

I haven't been able to get the truck to act hot since. I say "act" because I do not believe it was actually overheating that day.