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Discussion Starter · #1 ·
My 94 IDI overheats when I'm pulling a load uphill. Where do I start looking for the problem? There are no leaks in the cooling system. I've had this truck for 8 months now and have already put $2400 into it but I expected it since it has over 300k miles.
 

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Are there bubbles in your coolant tank when it's running and up to temp? Is your upper radiator hose hard when its hot (it's supposed to be if radiator cap isnt sealing it wont keep coolant under pressure and will boil). Do you have a real gauge or the factory gauge? What does the inside of the radiator look like when looking through the radiator cap? Is your clutch fan functioning? If you hav a real gauge, without a load does the thermostat always maintain 180-190?
 

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Discussion Starter · #3 · (Edited)
Are there bubbles in your coolant tank when it's running and up to temp? Is your upper radiator hose hard when its hot (it's supposed to be if radiator cap isnt sealing it wont keep coolant under pressure and will boil). Do you have a real gauge or the factory gauge? What does the inside of the radiator look like when looking through the radiator cap? Is your clutch fan functioning? If you hav a real gauge, without a load does the thermostat always maintain 180-190?
I have the factory temperature guage. The clutch fan engages very little when it gets hot, doesn't stay on while it's hot. When warmed up the temperature hovers around the center of the guage during unloaded driving. I will check all those other things. Thx
 

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Saying it overheats pulling a load uphill doesn't mean a thing without knowing what temp your talking about.

The fan kicks in hi speed if you want to call it that, it kicks in at around 135*F to 140*F from the air thru the radiator that heats the coil spring in the fan clutch. Normally the fan will only cycle for 1 to 3 minutes to cool down.

Without a real gauge to indicate the head temp, your just guessing that it's overheating.

If someone installed other than a Motorcraft or IH T'stat, that could be a problem. IF it's a Chine made, they are prone to have the supports break off and not control the coolant flow correctly. See pic to see the three supports, thin metal strips to dome. Shown is the correct T'stat.
 

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Discussion Starter · #6 ·
Saying it overheats pulling a load uphill doesn't mean a thing without knowing what temp your talking about.

The fan kicks in hi speed if you want to call it that, it kicks in at around 135*F to 140*F from the air thru the radiator that heats the coil spring in the fan clutch. Normally the fan will only cycle for 1 to 3 minutes to cool down.

Without a real gauge to indicate the head temp, your just guessing that it's overheating.

If someone installed other than a Motorcraft or IH T'stat, that could be a problem. IF it's a Chine made, they are prone to have the supports break off and not control the coolant flow correctly. See pic to see the three supports, thin metal strips to dome. Shown is the correct T'stat.
The temperature needle went past the normal range to the red and the overheating light came on and I could smell coolant so that's how I figured it was overheating.
The Tstat would probably be a good place to start. I'll get one from Ford parts and replace this one. Can you recommend a good sealant to use for this?
 

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I use Three Bond 1184 for everything. It seals up within 10 minutes, well you need to let it tack up for 10 minutes, then mate surface and its ready for oil/coolant in 10 minutes. Be careful with the thermostat housing, soak it in Kano Kroil or something, i did and still broke one of the bolts, i was lucky enough through soaking after removal to get the broken stud out with vice grips
 

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Discussion Starter · #8 ·
I use Three Bond 1184 for everything. It seals up within 10 minutes, well you need to let it tack up for 10 minutes, then mate surface and its ready for oil/coolant in 10 minutes. Be careful with the thermostat housing, soak it in Kano Kroil or something, i did and still broke one of the bolts, i was lucky enough through soaking after removal to get the broken stud out with vice grips
Hmmm maybe I should go ahead and get 2 new studs while I'm at it. It does have a lot of miles on it. Thx
 

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Well they are actually bolts, they became studs when I broke them haha. I just replaced then with 1.5 or 2 inch 5/16 of 3/8 grade 8 bolts. I can't remember the exact size I always have a few bolts laying around. I'd invest in some aero kroil, it's expensive but by far the best penetrating oil I've found, it even smells nice.
 

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I've had 3 of these, my last one had the heavy duty radiator & never thought about getting hot, current one runs a little warmer all the time & will heat up if pulling.

Maybe something to look into.
 

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The temperature needle went past the normal range to the red and the overheating light came on and I could smell coolant so that's how I figured it was overheating.
The Tstat would probably be a good place to start. I'll get one from Ford parts and replace this one. Can you recommend a good sealant to use for this?
Silicone RTV used correctly is some of the best I've ever used. Never seize on the bolts will insure that you never have to use any penetrating oil again. Some penetrating oil, and a good sharp rap with a hammer and punch usually loosens the stubborn ones that don't have never seize. If I'm not mistaken, the thermostat will come with a square ring replacement, and won't require any sealant, just put it together. If it is a gasket, a thin layer of silicone on both sides, and let it dry for about 10 minutes then assemble.
 

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What mechanics have used through the years for this and most all other applications is 3M Weatherstrip Adhesive on either the block or thermostat housing to hold the gasket in position, and a slight coating of the Permatex Aviation sealer (brown stuff) on the other side of the gasket. Actually if the surfaces are clean, no sealer is really needed, no reason why it should leak.
Unless someone has installed the wrong thermostat, it's a greater possibility your overheating problem is your fan clutch. When pulling hard at at least 2400 RPM or more, you should definitely hear your fan clutch lock up and roar when your gage needle gets to the upper area of the "hot" range. Mine has always done so, then the needle slowly creeps down to the lower "cooler" middle of the range while the fan is locked during long heavy pulls like going over the Continental Divide. And don't be led astray by this type of incorrect crap from another IDI site:

"once your speed is past 30-ish, the fan is useless anyway, as the wind over the radiator is more than a fan would pull over it. the fan does the most good in stop-and-go traffic, and when just stopped. but even climbing a steep hill at 35, there's plenty of airflow a fan isn't going to make a difference, but water flow sure will!"
The guy's obviously never towed much or definitely a flatlander who never saw a mountain.
 

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My truck was slow to warm up, which I realized later, and began to get hot towing on hills. Half way stuck non Ford thermostat was the problem.
 

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What mechanics have used through the years for this and most all other applications is 3M Weatherstrip Adhesive on either the block or thermostat housing to hold the gasket in position, and a slight coating of the Permatex Aviation sealer (brown stuff) on the other side of the gasket. Actually if the surfaces are clean, no sealer is really needed, no reason why it should leak.
Unless someone has installed the wrong thermostat, it's a greater possibility your overheating problem is your fan clutch. When pulling hard at at least 2400 RPM or more, you should definitely hear your fan clutch lock up and roar when your gage needle gets to the upper area of the "hot" range. Mine has always done so, then the needle slowly creeps down to the lower "cooler" middle of the range while the fan is locked during long heavy pulls like going over the Continental Divide. And don't be led astray by this type of incorrect crap from another IDI site:

"once your speed is past 30-ish, the fan is useless anyway, as the wind over the radiator is more than a fan would pull over it. the fan does the most good in stop-and-go traffic, and when just stopped. but even climbing a steep hill at 35, there's plenty of airflow a fan isn't going to make a difference, but water flow sure will!"
The guy's obviously never towed much or definitely a flatlander who never saw a mountain.
I can remember calling the weather strip adhesive "yellow death"
 

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Discussion Starter · #16 · (Edited)
I pulled the thermostat out and it was a motorcraft part but it was in 2 pieces. It was stuck but it was stuck open so I replaced it with the motorcraft tstat and made no difference. Ever since I bought this truck a year ago the overheating just gets worse and worse. I have noticed a slow but steady coolant drop in my radiator but never saw the leak but it is dropping much faster in the past 2 weeks and I put 2 gal in it yesterday and today it is below the fins again in the radiator but I can see the leak now. It is coming from the front of the engine with a steady stream leaking directly from the crankshaft. I cant see it coming out of the water pump but Im assuming its leaking from there. Could it be weak flow from the water pump causing all this overheating? I'm going to go ahead and replace the water pump. Is it hard to replace the water pump? Should I get the motorcraft pump or autozone? Are there any left hand threaded bolts? Do any of the bolts need rtv on the threads? Any tips?
 

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Biggest thing is the bolt lengths. The top two are a specific length so they don't hit the timing gears. I wouldn't use the AZone "house" brand myself but that's just me.
 

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The fan, mounted in the end of the water pump shaft is a left hand thread, and sometimes a real booger to get off.
 

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Are there any left hand threaded bolts? Do any of the bolts need rtv on the threads? Any tips?
No left hand threads except the fan clutch. Don't use Teflon tape on any bolts. Use a liquid sealer on the bolts.
 

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Discussion Starter · #20 · (Edited)
What liquid sealer should be used on the bolt threads?
 
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