Overheating. (3 Viewers)

[livelarg]

Howdy all,

My truck is having a little of an overheating issue.
It is fine when I'm driving in town, but when I get on the highway about 70mph or over, it starts to overheat. If I keep driving, it will really overheat.
But I can drive all day at street speeds and everything is fine.

I've flushed the system and put new thermostat, and the system is full. Doing that did nothing to help the overheating issue

Im confused that it is fine until I get up to highway speeds.
Any suggestions?

Thanks
Kent

 

[Malleus]

Replace the fan clutch

 

[jonheld]

^^^^^^^^THIS^^^^^^^^
AISIN FCT-004 or you can pick up a modified AISIN fan clutch from one of the vendors on the forum.

 

[livelarg]

I'm not questioning that this is the issue. But how would the fan clutch cause it to overheat on the highway and not the street?

Thanks for the quick reply!!

 

[LongDuck]

When was the last time you changed the Thermostat? Also, a common problem with this symptom is a radiator that's partially clogged with mud or foliage from water crossings. It's hard to see, but restricts enough airflow to cause overheating at the higher power and load levels that you see at highway speeds.

 

[livelarg]

Just flushed the system and put rust cleaner in it, and new thermostat.
That didnt change anything

 

[Kernal]

Do you see any bubbling into the coolant reservoir tank while the vehicle is running or after shutting the engine off?
Have you had to top off the coolant frequently ie: before you flushed the system? (topping off some is relatively common after flushing the cooling system)
Do you see vapor coming out of the tailpipe, more than usual, sweet smelling?
Have you noticed the level of the fluid in the overflow tank going higher than it used to be, staying elevated, and then find the radiator coolant level is low?
How is the engine idling/running compared to before it started to overheat?

 

[Malleus]

I'm not questioning that this is the issue. But how would the fan clutch cause it to overheat on the highway and not the street?

Thanks for the quick reply!!

The reason there is a clutch on the fan is that the fan is the only way to get air into and through the radiator when the truck isn't moving fast. When it is, the fan needs to get out of the way. If it's directly connected to a turning crankshaft, that's not going to happen. If it has a working clutch, it freewheels at highway speeds so that it doesn't fight the air being pushed into the radiator by the forward motion of the truck.

 

[use2bn83]

There are some good recommendations up above.

Is the cooling system pushing enough coolant out to overflow the expansion tank? Might be time to check the radiator cap, or replace.

A restricted exhaust system (clogged cats) can lead to this as well, and could be a follow on check if the usual suspects are eliminated. It would be far from the first time I’ve seen this. In Colorado, this usually rears its head when going up the pass.

Good Luck!!

 

[DodgeH8TER]

Howdy all,

My truck is having a little of an overheating issue.
It is fine when I'm driving in town, but when I get on the highway about 70mph or over, it starts to overheat. If I keep driving, it will really overheat.
But I can drive all day at street speeds and everything is fine.

I've flushed the system and put new thermostat, and the system is full. Doing that did nothing to help the overheating issue

Im confused that it is fine until I get up to highway speeds.
Any suggestions?

Thanks
Kent

Id honestly look at the water pump. If it's only happening at free way speeds it could possibly be that. You won't over heat in town because it moves enough fluid because your thermostat isn't always open in town where on the freeway it's running at full force the entire time. I don't know these rigs well enough with where or what runs the water pump. If it's on the belt simply remove the belt spin it and if it makes a grinding noise or if it stops almost immediately then that's probably the culprit. I could also see the radiator being clogged as an issue to. Was your coolant super dirty or if you look in the cap with a flashlight when the radiator is empty and it has tons of build up and corrosion then I'd look into replacing that first. But roll with the easiest stuff first like the thermostat. Then move to more complicated stuff like the water pump and radiator

 

[livelarg]

I listened for the water pump, and it seems to be ok, or at least not making noise that I can hear, seems to spin smoothy.

I going to check on a new fan clutch. Ive seen that mentioned in a couple of other threads too.

Thanks all, Ill update as soon as I put the new clutch on.

 

[DodgeH8TER]

I listened for the water pump, and it seems to be ok, or at least not making noise that I can hear, seems to spin smoothy.

I going to check on a new fan clutch. Ive seen that mentioned in a couple of other threads too.

Thanks all, Ill update as soon as I put the new clutch onon.

Well best of luck than. Hopefully it's not a major issue and it's something simple

 

[jonheld]

I'm not questioning that this is the issue. But how would the fan clutch cause it to overheat on the highway and not the street?

Thanks for the quick reply!!

Because these trucks are as aerodynamic as a brick.
At highway speed, there is a wave of high pressure air in front of the truck. The fan creates low pressure behind the radiator that allows air to flow through as opposed to around.
These trucks will NEVER cool properly without a functional fan clutch at any speed. You only think you're running at a reasonable temp around town because there's little load on the motor and the dash gauge has a significant dead spot. Once you set up an OBD2 monitor you'll realize this.

Another thing to consider is the fan shroud. It MUST be in place and intact for the fan to function properly.

 

[jonheld]

The reason there is a clutch on the fan is that the fan is the only way to get air into and through the radiator when the truck isn't moving fast. When it is, the fan needs to get out of the way. If it's directly connected to a turning crankshaft, that's not going to happen. If it has a working clutch, it freewheels at highway speeds so that it doesn't fight the air being pushed into the radiator by the forward motion of the truck.

Strongly disagree with this. The fan MUST provide low pressure behind the radiator to have airflow.
Went through this on my 91 FJ80 with an old, tired fan clutch and on my 97. Both wouldn't stay reasonably cool at highway speeds.

 

[lp2k]

Fan clutch - hands down
Been there in 2009

 

[landtank]

Fan clutches is easy to check. Go out for a drive where you know it will run hot. When you see the temp rise, pull over. Shut the engine off and check the fan for resistance. There should be a significant amount of resistance and if not it’s likely a clutch problem.