I'm about to inherit a similar problem as I am purchasing a 79 F250 with a 460 swapped in. The owner reports that on hot days (80 and above) the temp guage starts climbing after the truck has been sitting for 15+ minutes. He claims that if you open the hood, the guage go right back down.

He has put in a four core radiator, new thermostat, a separate trans cooler, flex fan, an intake baffle and a new shroud to try to remedy.

The only thing he hasn't tried is toying with smaller water pump pullies to spin the fan faster.

Is this something that can be cured, or is this the to be expected for this size motor in the truck?

Thoughts?

 

I think the drop in temp *On the Gauge* is coincidental.

Ford's gauge system sucks sometimes.

Next time the engine heats up, just rev the engine to see if the temp drops.

btw, I see you were in the basement to find this 2 year old thread &

Welcome to FTE!

 

Boy, you sure got a lot of postings on this one. Alot of interesting replys. I will remember some of them, great ideas. You might consider turbulance from the fan being so close to the radiator. At higher speeds the turbulance could be blocking airflow from getting through the radiator. You might take the fan off and make a quick trip down the highway to see if it cures the problem. I definately wouldn't do any city driving with the fan off. Other than that I don't know. Everybody else has covered all of the bases. I have been pulling a 6500lb 5th wheel trailer with my 460 for years with no overheating problems. You might also advance the timing a few degrees, mine runs cooler that way.

 

First thing Stanz needs to do is get rid of that flex fan and install the stock OEM thermostatic controlled clutch and fan assy.

What is the "intake baffle" you speak of?

 

The intake baffle is a shield that sits under the intake to shield hot oil from splashing onto the underside of the intake.

Is there a difference between the stock 400 fan and the fan I should be using for a 460? The seller claims to still have the 400 fan.

I'm confused by Mil1ion's comment that opening the hood and the drop in the guage is coincidental -- if it's consistent, how can they not be correlated? When he suggest that I rev the engine, what he is mechanically expecting to happen to make the temp drop?

Thanks!

 

I've inherited a 79 f250 with the same problem! Previous owner swapped out radiator, water pump, t-stat etc.. and couldn't solve the problem. I bought the truck for very little. I have an experienced ford truck mechanic working on it as we speak. He plans to check the cooling system, compression etc.. I'll keep you informed on what he finds. I have a suspicion this is a tricky head gasket problem.

 

One thing I was curious about with the old 2002 post that may apply to the new post are the comments about the fan shroud and position of the fan in relation to it. A fan is supposed to be installed so it spins right in the opening of the shroud is it not? In some cases we install the fan very close to the rad, thinking (incorrectly) that it improves cooling. If I understand the theory correctly this prevents the fan from doing an efficient job, contributing to cooling problems. Does this sound right?

 

I agree with the fan-shroud arrangement and the proximity the fan is with the radiator causing problems. I may know a theoretical thing or two about this. A fan close to the radiator may not be the most effective way to maximize airflow past the fins, there is an optimal spacing from the radiator. This has to due with the "turbulent" area close to the fan that actually pushes air toward the radiator as it rotates. This happens at small distances from the fan, within a couple inches.

Also, the fan shoud plays an important role. It reduced the flow volume. This produces an noticeable drag through all the fins, not just the area adjacent to the fan. The reduction of air flow volume induces a pressure gradient of flow between the exit portion of the shroud and the front side of the radiator.

Theoretically, the problem arises when the turbulent forces exceed the pressure gradient induced by the shroud-fan combo. I have never seen a net flow of zero but I do think this non-optimal arrangement can induce overheating to some vehicles in hot weather at idle.

If my vehicle overheats I never mess with the stock fan-shroud arrangement. I assume the engineers do their job and have configured the optimal arrangement. I look for bigger fishes to fry!!!

 

Uhhh, the fan shroud does not reduce flow volume, it increases it. The shroud prevents air from flowing from the high pressure zone behind the fan back into the low pressure zone in front of it increasing efficiency. The shroud also makes the fan draw thru the entire radiator surface if it is a stock OEM type. There are aftermarket dress up shrouds that are nothing more than a ring around the fan that do not provide a draw thru the entire surface of the radiator.

Stanz- The intake oil baffle has little or nothing to do with engine temp.

 

Thanks for all of the quick replies and lively discussion. Got a little more info from the seller.

He has already replace the head gaskets and water pump: no change, no bubbles in the coolant.

He also notes: idle is at 750 RPM, this is where the temp rises. He claims that if you put a toe on the gas and raise it to 1000 RPM, the temp goes back down. He seems to think pully size is not spinning the fan fast enough at 750, and is at 1000+.

It'll be two weeks before the haulers get it to me for me to check it out myself.

Thoughts on pully size?

 

This sentence
Quote:
He also notes: idle is at 750 RPM, this is where the temp rises. He claims that if you put a toe on the gas and raise it to 1000 RPM, the temp goes back down.

Should explain

This question
Quote:
When he suggest that I rev the engine, what he is mechanically expecting to happen to make the temp drop?


Yes, That's what I was saying.

Remember this for always.
You can't assume that a Ford Gauge is accurate.

If an engine is over-heating it will eventually come blowing out the overflow tube.

That's when you know there is an over-heating problem.

The best measure is to get a 7 blade fan with thermo clutch.


My 78 has a problem shared by many here on FTE.

I couls be driving down a shaded highway up in the mountains at 9000 ft. and my gauge will zing over to the HOT side of the gauge.
3 raps on the dash abd ut comes back down to normal & will stay there for another 500 miles.
Then months later it might do it again.

If you are ever looking for a 7 blade fan with Clutch, let me know.

I hope I have helped somewhat

 

Fan shroud is a conicle structure. This decreases volume of flow which in turn increases pressure. Fan initiates rate of flow.

 

nuclear- The fan shroud increases the flow thru the radiator over a fan spinning in the air. You are miss-applying theories to the real life overall effect of the shroud.

 

Torque1st- I appreciate your administratorship. We are in agreement. But I feel you had misinterpreted my post that tells of a decrease in volume as a decrease in rate. Volume reduction is beneficial because it induces the pressure gradient. Primarily, the shroud makes use of this gradient to pull air somewhat uniformly through the entire surface of the radiator, as an added benefit the shroud eliminates cross currents from the underhood environment, making the flow effective. The fan drives the system. You had stated correctly that the fan increases flow but I would argue that at great speeds (above 70mph) the fan is of little added benefit.

 

Actually the transition from "fan powered flow" to "vehicle powered flow" comes at about 35mph give or take depending on aerodynamics, long before 70mph. You can read all about it in several SAE manuals. Check with their website. That transition is why those of us with experience ask users whether their truck overheats in the city or the highway. Those are some of the many clues that we use to determine where the problem is. Just the knowledge that comes from long experience.