Hey guys just needed some help. My engine overheats when running down the highway, but the thing that gets me is I can let it idle all day even with the ac running and it will never overheat. I was told it could be the fan clutch but I have no idea. Any ideas anyone? thanks for any help.

 

Welcome to FTE

Overheats?....or the temp gauge goes higher than a normal city short trip?
My 92 5.0 will go higher than "normal" when I run down the highway at 70 as opposed to stop and go city driving. I've been watching this closely too. The highway trips are 20-30 miles and the gauge goes back down after a few minutes of off highway driving.
Just last week I went on a 300 mile round trip........at 70-80 mph most of the way. On the way up I didn't need the A/C and the gauge read just a little higher than my normal reading. On the way back I ran the A/C and defrost and she ran almost "normal" all the way. Go figure.

I had a 305 with a bad fan clutch once and similar symptoms..and it cycled the A/C on and off due to heat/pressure build-up. That's how we found it.....testing the A/C for high pressure. Clutches do go bad but the purpose of a clutch is to slow your fan at high speeds/rpms when you don't need it.
In your case....I'd lean toward a partially clogged radiator or not having a good 50-50 mix. Try a back-flush and make sure it's clean the add the right mixture. Stick a new thermostat in and see what happens.

You can try turning the fan and wiggling it back and forth .....there should be no play in it or any noises......should also feel harder to turn with the engine off.

Good Luck
Bob

 

Hmm... I dunno about all that Bob. My temp gauge sits LOWER on the highway than it does in the city (and it very well should). At high speeds the fan wouldn't be able to push as much air as the wind is pushing through the grill anyways, so it just disengage the clutch and allows the fan to free spin (per say). Since I put in my electric fan I have been able to experiment with temperature a little bit. Driving anywhere less than about 35-40mph, the fan MUST be on, or my temp gauge climbs, and climbs FAST. Once I hit 40mph I hit the switch to the turn the fan off and the needle never moves a hair, the wind keeps the engine MORE than cool. If your temp is increasing on the highway then I would suggest that YOU might have a bad fan clutch (as well as the OP) which might be hindering air flow at highway speeds.

To the OP, check your fan like Bob said and see if shes got play or wiggle room, but I'm not sure that is going to be a sure fire way to check it. I'm really not sure of a good way to ensure proper fan clutch functionality, maybe someone else can chime in about that, it might just be worth your while to grab a few cheapies from the junkyard and try them on for size, to see if anything changes. If you're in California you're welcome to throw my old clutch fan in your truck and have a go with it, it was working perfect when I took it out a few weeks ago. Good luck buddy.

 

Yeh I know Chris........Mine does opposite in most highway driving........except this last longer trip.......weird I know....I'm going to watch this thread and see what other answers we get. Mine should do like yours......and it could be the clutch.

Bob

 

The only way I've someone test the fan clutch was at a radiator shop. He took an old piece of radiator hose and stuck it the fan on the backside while running to see if he could stop it with ease. Which it did not, it slowed down but did not stop.

I for one am not going to stick something in a rotating component.

 

It definitely overheats. Before I even started driving it I changed the hoses, thermostat and flushed/filled. I'll take a look at the fan and see what I got.
Chris, how far from sandog are you and what would you want for your old fan clutch? (if thats the prob)
And again thanks for your help.

 

I'm afraid I'm up in norcal buddy Google maps shows a 6-7 hour trip to get from here to there. I would try your luck at the junkyard and pick up a couple clutch fans. They shouldn't be that expensive and odds are ONE of them is going to work. They're easy to remove, just unscrew the four bolts on the pulley where it attaches, slide it off the center shaft, undo the two screws on the shroud and pull it all out together. Should take no more than 5 minutes. I would try to get one that is still in the truck because I heard they can go bad if not stored upright (fluid inside).

 

Hmmm, the ONLY time my fan needs to be on is when I am in bumper to bumper slow moving traffick or a dead stop for a 5 or more minutes. You must be doing something wrong with your truck.

As far as the OP's case, an easy way to tell if the fan is the problem is to take off the fan then get on the freeway when there is no traffick. Just go to the freeway, take off the fan and shroud (easy to do) then go for a drive. If it does not overheat you found your problem...if it does, pull over, put the fan back on, limp home and go back to the drawing boards.

 

I'm gonna bet the fan is NOT the problem. At 40 + MPH, should be able to throw the fan away and not miss it at all. That is one reason we have clutch fans to uncouple the drag of the huge fan at highway speeds.
The reason it is over heating is the coolant is not circulating properly at highway speeds. That is the only way the truck can overheat
Why is it not circulating properly? Most likely candidate is the radiator. Ever put any stop leak in it? How is the heater output? If the heater output is poor, and the truck overheats at high speeds, most likely both radiator, and heater core stopped up from crude and corrision or stop leak. If your radiator is stopped up bad enough to cause overheating, I think it is beyond the backflush in the driveway. Sounds like time for a new one. Properly maintain the new one and it will last the life of the truck.
Next possibility is either thermostate not opening all the way, or water pump not moving enough water. Thermostate is easy to test on a stove with a candy thermometer. Water pump output is not easy to test.
Last possible cause I can think of right now is a leaking head gasket. I certainly hope that is not the problem.
Good luck Frank

 

If the problem is the raidiator then how do you explain not overheating at idle and only overheating on the hiway?

 

If the radiator is partialy plugged, the water can flow thru it, but not fast. The clutch fan and low cooling requirements at slow speeds are keeping it cool. When the engine is turning faster and making more demand on the cooling system, the water is still only able to slowly flow thru the radiator, and can not provide the required cooling.
I believe that is what is going on if the radiator is the problem.
Like you said about your truck, normally you don't need any fan at highway speeds. The tremendous rush of air thru the radiator does the job under normal circumstances.
Frank

 

Get rid of fan clutch, go with high rpm flex fan they work great. changed mine ten years ago, no problems.

 

Your problem is either insufficient circulation or inefficent radiator.

Even though vehicles appear to heat up at idle, this is due to insufficient air flow at idle........actually the maximum generated heat within the engine is at higher speeds.

Have you tried checking the outside of the radiator for mud or debris within the fins ?

 

I am not saying you are wrong regarding the guys problem, and I am not saying I have the solution to the problem, but I am saying that what you are saying does not make a whole lot of sense. The engine turning faster alone does not increase the temp of the coolant because the water pump also turns faster. Some cars have a engine temp sensor that increases rpm at a certain temp to spin the water pump quicker to help cool the engine. With the water pump turning faster + "that tremendous rush of air thru the radiator" even with a plugged raidiator at highway conditions unless we are talking about a completely plugged radiator which would not even cool at idle (his will). I would tend to think that LOAD would increase the heat build up in the coolant more so than an RPM increase and flying down the freeway with an empty truck in low gear at about 2000 or so rpm (he did not say anything about towing or hills) isn't much of a load as far as the motor is concerned and between the air flow and water pump speed that should be fine.

The last time (and only) I had a partly plugged radiator w/ a mechanical fan the only time I was not overheating was when I was on the freeway.

 

"The engine turning faster alone does not increase the temp of the coolant because the water pump also turns faster."
I agree with this statement, but it is true only if the coolant is able to loose the heat at the radiator. If the radiator is plugged and not able to remove enough heat, the higher heat load will cause the coolant to heat up.
I'm trying to think of a good way to explain what I'm thinking.
Let's assume for an example, not real numbers
100 rpms gives 1000BTU
1000 rpm = 10,000BTU
2000rpm= 20,000btu.
Suppose the total capacity of a new radiator is 150,000BTU, but the partialy plugged radiator capacity is only 15000 BTU.
At rpm's below 1500, the coolant temp will be determined by the thermostate. Above 1500 the temp will start to climb.
It doesn't matter that the water pump is delivering 20,000BTU to the radiator if it can only shed 15000BTU.
I have worked on and driven some real clunkers over the years and seen this problem more than once. Once I had to drive 100 miles on interstate, in the summer with the heater on full blast and the windows down. Could not go above 40 or the temp gauge would peg out. Had the radiator rodded out to solve the problem.
I hope TEX250 solves the problem so we will all know what was wrong with it.

Frank