Overheating on highway only. Whats the problem?

[Fordum]

I'm still turkey hunting, so I don't always manage to finish my thought. I actually had something else in mind when I was writing about the load on the fan at speed, but it just drifted away in the breeze.
Putting that big load on the fan, and it takes the cube of the speed to drive it. Which means that if you double the amount of air you ask it to move, it takes 8 times the power, 2X2X2.

That also loads down the fan belt the same amount. Worn belt, weak tensioner, or just a bad brand of belt that is too hard, is a double whammy.
Not only does it cause the fan to run slow, but it slows down the water pump.
A fan belt is going to be warm due to where it lives, but after a hard run it should not be hot.
Might feel of it and see.
If it puts hot melted rubber on your hand, thats a clue right there..........

 

[miniwally]

I was under the impression that as long as you werent pulling a hill or load that you should all but be able to remove the fan at highway speeds due to all the air rushing through the radiatior naturally. Is that not true?

Yes it is a clucth fan. Nearly brand new with only 1000 miles on the truck it came off of. Not to say that its good.

Im running a 195 stat that is also new.

LOTS of dudes out there run the steam port line into the water pumps and have no problems. I figure the t-stat housing should be the same no? It stays right at 195-197 idling and around town. Also cools back down to 195 within a minute or two after getting off the freeway.

I went through your build thread and I think you have two issues.

One your fan isn't into the shroud at all in the pictures I saw, if you changed this disregard the following. The fan needs to be roughly half way into the shroud, like it shows in the one picture the fan is just whipping the air in the engine compartment up not pulling air in the shroud out. Theory saws you don't need the fan for highway speeds but reality saws you do. They fans do kick on, mine in my D-max does a lot during the summer when you work the truck hard.

Second is that I think you have a steam port line issue. I need to spend some time pondering the idea of installing the port in the lower radiator hose like you have done by putting it in the thermostat housing but my initial thought is that you need to move it. Not sure yet though.
I think there is a pressure issue with your setup and you have trapped air in the block.

 

[y5mgisi]

Now that im thinking more about it, i dont know but perhaps i have given it the "broken straw" effect. Where instad of creating "vacuum" of sorts and sucking the coolant through the lower hose, it is loosing that suction through the steam line. This, i suppose, could limit how much coolant it is pulling through the lower hose. I thinki first things first i will move the steam line to the water pump where other folks have it on the return side. If that doent fix it i will probably get something like this that would allow me to re use and space my old 350 fan.

http://www.4wheelparts.com/Heating-...dium=froogle&utm_campaign=product&emlprox=out

 

[miniwally]

Now that im thinking more about it, i dont know but perhaps i have given it the "broken straw" effect. Where instad of creating "vacuum" of sorts and sucking the coolant through the lower hose, it is loosing that suction through the steam line. This, i suppose, could limit how much coolant it is pulling through the lower hose. I thinki first things first i will move the steam line to the water pump where other folks have it on the return side. If that doent fix it i will probably get something like this that would allow me to re use and space my old 350 fan.

http://www.4wheelparts.com/Heating-...dium=froogle&utm_campaign=product&emlprox=out

That's what I'm thinking, where others have put the port in the water pump is technically in the upper radiator hose. The factory port is in the rad right next to the upper hose port.

Your line is in the lower hose basically and I think that is where your issue is.

Like I said we put a T in the upper radiator hose/line on the race car and it has never had an issue even in hot weather going slow. Course that could also be the 19"X36" radiator with 2 16" spal fans as well

 

[big pappa b]

Any word on the overheating issue yet?

 

[y5mgisi]

No i havent messed with it yet. Going to first move the steam line and try that. If that doesnt work i will do something with the fan.

 

[76zimmer]

Clutch fan?
There is a huge load on the fan when you are at speed. If some of your clutch fluid has leaked out, it may be slipping at high RPMs.

The fan shouldn't be coming into play while running down the freeway. If it was related to the fan or shroud you would have more overheating issues around town and idling.

The only time I have had overheating issues while on the freeway was blockage of the radiator (got into a deep mud hole and clogged the radiator)...faster I went the hotter it got.

From personal experience:

My 99 6.0 was overheating when at highway operation...the engine being in the 2500rpm range (in drive) and when in town it was normal acting.
Replaced only the fan clutch and it is normal in all aspects now, and now you can really hear the fan moving the air too!

 

[y5mgisi]

Yea its rare that you ever hear mine pull air.

 

[1989gmcbeast]

Se problem

My 89 k5 with 350/ 60 over 600edelbrock 1406 is overheating on the highway but not cooling down very fast. The radiator is a used one bought for lack of funds during the engine swap nov 13. It's a sudden problem that only started after I tried to use ac in on one of the warmer days. It has since started overheating even without ac use. Water pump was new with engine swap.

 

[Kain]

Try changing the thermostat

 

[Kain]

Also if your running a clutch fan check it,make sure it spins freely

 

[Jessie James]

Water pump was new with engine swap.

Do you know what the water pump looked like before it was installed?

if you have one with cheap, bent metal fins, that is likely your problem. If you have one with a cast impeller, you should be fine. I had the exact same problem and had the cheap-o impeller. I swapped it and the problem went away.

For example, the impeller on the left may not move water very well, but the one on the right will.

 

[1989gmcbeast]

Fixed!!!

It was the radiator. I took it out today and the entire front was packed full of dirt and other grime. It wouldn't come out with pressure washer so I swapped it out. All fixed

 

[kennyw]

First thing you need to do is test or replace the thermostat. Just went through the exact same issue with my FIL's hot rod. It was a brand new but defective thermostat. You can test it by dropping it in a pan of water and boiling the water on the stove. Should open up fully by the time the water boils.