Hello all, first time on this forum, hopefully someone can help.

Here is the situation. Just recently acquired a 2001 Navigator 4x4 with 130K on it. Had it checked out and all was good, and the thing runs great with no issues other than the AC compressor as of now. Friday was the first time I was pulling my 32' travel trailer, which is 6900 pounds dry, and a little under 8000 pounds with our stuff in it. The capacity on the Navigator is 8800 pounds, with the 5.4 Liter 32V motor, so I am almost 1000 pounds under capacity. The truck was towing PERFECTLY.....it was actually much better than any other truck I have owned for towing, probably because it is so heavy....not sure.

Anyway, about 45 minutes into the trip, driving 65 miles an hour with the overdrive OFF @ 2500 RPM the whole time, the truck started overheating. Pulled over, added a little fluid (the antifreeze was a little low, but not bad....), let it cool off, and started back on my way. There were no noticeable leaks anywhere, and all fluid levels were maintaining. Oil pressure was good, there was nothing else i could see that was making it do this. Another 15 minutes into the trip, it started again. Pulled over and let it cool off. From that point on, I turned the overdrive back on and drove much slower so I could manage the RPM's (to keep it around 1500) and the transmission shifting as to not damage anything. From that point on I was able to keep it from overheating until I got to the campground.

Did some research, and the only thing I could really do at the campground was to change the thermostat, in the event that was a problem. Apparently those are prone to failure in those trucks. So I start back home on Sunday and I drive 65 MPH with overdrive ON so I could keep the truck around 1600-1700 RPMS, and there was no problem, with the temperature in the normal range for over an hour of the trip. Pulled into a rest stop and thought I would try it with overdrive OFF (as I should be towing) - and within 10 minutes of getting back on the highway the temp was danger high so I stopped again and let it cool down, driving the rest of the way with overdrive ON so I could keep the RPMS down again, and all was well.

Here I the things I checked for, and all seem good:

1) Both main lines coming to and from the radiator seem to be close in temperature and normal.
2) Both lines going to and from the heater core seem to be the same as well
3) No leakage in the cooling system at all from what I can tell
4) Brand new thermostat - operating correctly
5) Fan is working properly, sucking air into the radiator as designed
6) Replaced the reservoir tank cap in the event it was letting air into the system
7) Drive belt is in good condition and all functions of the motor are working correctly and withing range from what I can tell outside of the AC compressor (clutch - pulley is spinning freely)
8) All fluid levels are good and maintaining proper levels

This is mystery and I can't get a good answer on this. If it were the water pump impeller fins, I would see overheating in normal driving conditions, at least that what I would think..... I drive distances frequently with the truck and never had any issues at all.

Any recommendations??? Please help!!

Thank you!!

 

You would prob get better - or at least more responses by putting your problem in the NAVVY forum, here: Expedition & Navigator - Ford Truck Enthusiasts Forums

 

Why are you towing with OD off? If transmission was not hunting no need to do so. You are fine using OD to tow. Not sure why you think you have a problem.
Steve

 

Off the top of my head, reasons for overheating, in no particular order:
1. Low on coolant
2. Incorrect coolant mixture
3. Loss of pressure in the system - bad water pump
4. Clutch fan isn't working right. When the engine is hot the fan should be stiff to move by hand. At 65 MPH your clutch fan shouldn't have to do much so I doubt this is the problem.
5. Blown head gasket
6. Air in the coolant - this is an easy one to fix, I did it on the side of the road today
7. Corroded radiator
8. Radiator fins are caked with crud - another easy one to fix. Clean it!
9. Bad thermostat that stays open all the time

 

Certainly lots of possibilities. What do you make out of overheating, but not when in overdrive?

Steve

 

Belt slipping on water pump when running at higher rpm when not in OD?

Steve

 

Higher RPM and the engine is working harder. Higher stress on the engine may be hitting a threshold with the head gasket.

Sean, open up the radiator and coolant overflow caps while the engine is cool. Run the engine long enough for the engine to run through a cycle or two of coolant. Watch the neck, looking for bubbles. If you have a pressurized overflow tank the bubbles may also been seen there. Increasing the engine RPM may be required. Bubbles = bad head gasket.

Check your engine oil. If it isn't normal (looks milky) then bad head gasket.

What does the smoke coming out the tail pipe look like? White = bad head gasket.

There is a bit of dilemma when it comes to temperature management of an engine and transmission. Transmissions really like it when an engine is running at higher RPM because that pumps more fluid through the transmission keeping it cool. But too high of RPM can be bad on the engine if there is insufficient air flow.

 

Yes, but the OP notes engine seems to run fine and pulls the load fine in OD. Agree at higher RPM more heat is generated, but still -. Just kind of an unusual situation.

Steve

 

Definitely odd to have more problems with the OD off.

Bad water pumps usually act the other way. Increasing RPM usually brings temps down if the pump is not moving the right amount of coolant at a given engine speed.

Plugged radiator or slipping belt would be my guess.

Fan clutch would be another guess. Listen for it at start up. It should howl like an banshee for a few seconds after sitting for a while. In my experience, of you don't hear it when you first start, its not working right.

The lower hose on the radiator should always be at least 20 degrees cooler than the top, and thats worst case. If thats not happening, then the radiator isn't doing its job.


Thats my guesses.

Wonder if mark k. Could be any help? Did some time in the cooling department and might have some unique thoughts or experience.

 

The way I was thinking about this question is what changed when a vehicle moved through the air at a given speed and the only variable that was changed was engine rpm, which is the variable the OP referenced monitoring.

Air movement through the radiator should be the same at a given speed, I think, and most of the variables we would agree lead to overheating would be unchanged.

If the fan clutch were inoperative or failing, would it not have equal impact in either condition?

I don't know, but interesting situation!

Steve

 

I haven't seen anything that says what temperatures have been reached. Is it really overheating? I've had people tell me their transmission is overheating because it is over 200F. That's normal. Without knowing what coolant temps have been seen I don't have any help.

 

Mark,

I agree with your comment, but can not wrap my head around the relative differences between the temperatures (gauge reading I guess) the OP posted.

If we forget about the issue of whether the engine is actually overheating, while driving down the road in what sound like moderate conditions, should there be an marked reduction in temperature in OP versus a lower gear at the same MPH?

It is the situation that is the greater curiosity to me rather than the overheating issue.

Steve

 

My recommendation is to get something so that you can find out some temperatures. You could install an aftermarket coolant temp gauge, or get an infrared gun to read the temps. How hot is this really getting?

The only thing I can think of that even comes close to matching the symptoms is a bad fan clutch.

 

I read this to mean that the factory gauge was reading at or near the top of the scale.

If that is true, then it is safe to say it was too hot, barring a faulty gauge/sender. An IR gun would be an easy way to verify the gauge.

Is the fan capable of moving more air through the radiator at 65mph? I guess anything that increases the pressure gradient across the radiator will help.

Something has been compromised, whether it is airflow across the radiator, or coolant through the radiator.

Hopefully the OP will get back to us

 

This sounds a lot like an internally restricted radiator. While it may still have enough cooling capacity to keep the engine cool at lower RPMs, the coolant is restricted and flowing through generally a small part of the radiator way too fast to be effectively cooled at hi RPMs.

It's been many years since this has been much of a problem now that pre-mixed anti-freeze is sort of the normal go to for the average driveway mechanic. Tap water/anti-freeze mix isn't terribly friendly to radiators.