Sorry not sure on your fan, but, if it has the clutch, might be it's not kicking in and spinning the fan at engine speed when heated.

 

how do you check the fan clutch for proper operation?

 

Couple of things to look at and listen to, first, grab hold of the blades, not while running of course! and try to spin them, they should turn, but with a good amount of drag. Next, try to "wobble" the blades, there should not be any play in the clutch unit up/down or side to side. Lastly, when you start the truck, you should notice a whoosh of air movement for the first few seconds, then dies off, this is normal, when the truck starts to overheat, open the hood and listen and feel for lots of air movement, should have it and it should be rather warm air blasting you. Usually they just use some type of bi-metal strip in there that when warmed by the minimal air coming from the radiator(that's why they do not disengage completely)it heats up and locks the fan to the engine until cooler air "shrinks" it again, this is very noticable in our vans when idling even in cooler weather, no mistaking the fan just kicked in or out. When mine went, I just replaced it with a heavy duty flex fan. It was much cheaper, but, pulls lots of air at idle and up to 2000 rpm's or so, then the blades give and flatten out to reduce drag. You should be basically cooled by the air flow from forward movement by then. This also reduces the weight the water pump bearings must carry. If you go this way, you will need a spacer to mount at the correct location in the shroud due to the lack of spacing taken by the clutch. Hope this helps.

 

I run 18 degrees intial timing with an additional 6 vacuum advance with no problems on a "built" motor. I am 5,000 feet above sea level though. I used to have the heating problem but mostly cured it with a new heavy duty "RV" style clutch fan from pep boys. Don't remember the brand name. About $40.
1977 Ford F-100
400m/c6
280,000 miles
Stock on the outside
modified/rebuilt everything

 

First if you suspect the fan i would see if the temp drops at cruise speed going down the road at about 55. If it does id say thats it if it doesnt it could be many things. I know 18 degrees is way to far advanced for a stock 400 at idle. Did you uplug the vacuum hose when checking the timing? As far as the overbore goes im sure it depends on the casting of the engine but my 400 in my 80 F350 is bored .060 over (yes thats right 60 over)and i can pull the hell out of it and never watch the heat guage rise one bit. But thats with a 4 speed and low gears.

 

I do notice the rush of air at first start then it gets quieter, so the clutch is ok, I suppose.. I think Im going to get a flex fan, do they carry "fan spacers" at most auto parts stores?? I used to work at a few auto parts stores when I was a teen , and I dont remember anything like that...but Im gonna drop in tommorow
PS how far from the shroud should the fan be?
77'FORD F150 XLT 400

 

Yes, they will have the spacers somewhere around the fans, usually one and two inches deep. The best possible placement is at the smallest opening of the shroud. This way it can't suck air from around the opening. You want to measure the opening and get the largest that will fit, I think I went with the 19", even though they called for an 18". Do realize that you will lose a little mpg when toolin' around town and you will hear the air movement at idle (I think this is part of the reason behind the use of them as well as fuel mileage). However, been to Texas during the summer and can understand why you need the air movement, mine works very well with a/c also, and this in front of a breathed on 460 with stock 351M radiator, never goes much above 190 unless pulling a very long hill in 105 temps, when the tranny's running hot. By the way, really did enjoy my stay around San Marcos, Lockhart(home of BBQ) and Waco. VERY nice people down that way (great steaks too!)-sorry I had to come back here!

 

do you mean that these flex fans make loss of mpg?? or the OE fans?

https://www.ford-trucks.com/dcforum/User_files/3a9df0394b631ce6.gif

77'FORD F150 XLT 400

 

SEAN,I WOULD TRY USING A NEW THERMOSTAT RATED @ 160 DEG.,A FLEX-FAN OF AN ELECTRIC WITH THERMOSTATIC CONTROL.THIS FAN CAN BE WIRED FOR A SUCKER OR A PUSHER DEPENDING ON HOW IT IS MOUNTED.ALSO CHECK YOUR RADIATOR CAP (PRESSURE TEST IT).YOU CAN ALSO GET AN ADDATIVE CALLED "40 BELOW" THAT WILL GREATLY HELP YOU.I USE IT IN MY INTERNATIONAL 4700 WRECKER.HOPE THIS HELPS YOU.

 

Ok, I hesitated about saying something before, but when fozzy
asked about mpg I have to give my opinion. I hate flex fans.
They are noisy, and they fly apart. They are horsepower robbers.
I had one on a car that I swapped the engine in. It flew apart
and luckily didn't go through the radiator but busted the fan shroud. A friend of mine wasn't so lucky. He did the 400 to
460 swap in a 79 f150 and was driving down the interstate when his flex fan flew apart and went through the radiator leaving him stranded. I thought this was a fluke until mine flew apart on me. I thought it would be less load on the water pump bearings and give me some more horses, but it puts a terrible
drag on the motor at high rpms and I can't stand all that noise.

 

Just a couple of notes:
Ford made a thermo controlled vac advance for the FE engines that would pull vac from one source when hot and another when cold. I was told that this would change the timming when the engine started to overheat and it cooled it down. Back the timming down and if it makes a difference but you loose performance, consider the thermo controlled vac adv setup.
ProBlend makes cooling products for oil, water and tranny, the 40 below works great.
The fan should be 1/3 the way into the shroud. Run about 70% water not 50/50, as water transfers heat better. Also, an engine oil cooler might be a good investment. Edelbrock makes excellent alum water pumps and they flow more than stock.
I replaced the cast iron impeller water pump on another car with a stamped steel one and noticed it ran hotter. They make backing plates for the impeller that increases flow about 30%. Also, different size pullies might help to, I used the stock ones for and A/C truck and they make the water pump spin faster.

 

Sorry 'bout that Fozzy,
That really didn't make much sense did it? Well, what I should have said was that you will lose a little fuel mileage with the flex fan, due to it pulling air all the time at low speeds (this seems to help the a/c a lot though, especially off-road and in town). I really don't believe I lost mileage much at all if any. Air noise will be there all the time also, (I don't notice it over the exhaust), that's the reasons behind the stock clutch fans, less noise, better gas mileage, and remember, not to long before our era of trucks they only used fixed blades. Have had mine for at least 12 or 14 years and never had any problems even when it was "treading" a little water. It is of the stainless steel type and was not the cheapest made, no rivited blades sections on it, all one piece, nothing to fly apart, but do expect that some day it will start stress cracking. But it does pull the air and when revved at a stand still, the engine/exhaust noise masks any noise it makes, there is also not much more noticable air flow at higher rpm's than at idle when sitting still. If you do go this way, make sure to check the bolts after it warms and cools a time or two and do use some lock-tite. Once again, sorry about any confusion, was not in any way intended, hope you have yourself a fine weekend!

 

I run a Flex Fan also, figured a little loss of hp was a fair trade for not having a clutch fan slipping and burning up my hard work I put in this beast. Also I run a 165' thermostat, Oil cooler and transmission cooler, two 10" electric fans mounted in front of the oil and tranny cooler which are mounted in front of the radiator, no cooling problems here.
Couple of things you might check:
Hoses have the spring in them, as when it heats up they tend to collapse and shutdown cooling.
Take top hose off of engine when cold and check to see if coolant is in there, have seen a rebuilt engine suffer from vapor lock and overheat at idle.
Since it is overheating at an idle I definitely recommend the flex fan, superior air flow at idle.
Take out the thermostat, takes longer to warm up but gives max coolant flow. Also will tell you if thermostat is the culprit.
Hope it helps.

HeavyMetal (Rod)
1977 F100 429CJ bored 30 over, Heads milled 30, edelbrock performer cam, intake, lifters, valve springs, Flat top forged pistons, polished and ported, Holley 750 Legacy, Hooker Super Comp. headers with dual Hooker Comp. exhaust and Hooker dual resonators, B&M C-6 racing tranny, with a TCI Breakaway 2600 flash stall converter, 9" rear with 2-72 gears.

 

remove the thermostat?? will the radiator have a chance to work??? I havent got the flex fan, I just got back from San Antonio,but I will be putting one on in the AM, will post results

https://www.ford-trucks.com/dcforum/User_files/3a9df0394b631ce6.gif

77'FORD F150 XLT 400

 

If take out the thermostat you allow coolant to flow from the block to the radiator 100% of the time. You of course seal the housing using a gasket and sealer, just no thermostat. Will take longer to heat up but will increase cooling, should let you know whether your Thermostat is good or bad. It won't hurt a thing.
Out of curiosity what heat range are your plugs, some engines don't respond well to plugs in too high of a heat range.
Keep us up todate!
HeavyMetal (Rod)
1977 F100 429CJ bored 30 over, Heads milled 30, edelbrock performer cam, intake, lifters, valve springs, Flat top forged pistons, polished and ported, Holley 750 Legacy, Hooker Super Comp. headers with dual Hooker Comp. exhaust and Hooker dual resonators, B&M C-6 racing tranny, with a TCI Breakaway 2600 flash stall converter, 9" rear with 2-72 gears.