Howdy fellas,

Been a while since I've been back.

My '91 7.3 IDI 4x4 is having cooling issues and I was hoping to get a little help diagnosing the problem, or choosing which repair path to take. Forgive the long-windedness... I like to give a lot of details.

A little background: I've had the truck almost three years and I've honestly never even noticed the temp gauge move before and thought it was broken (speedometer is way off as well). Then I sat in a line for thirty minutes at the dump on a hot day and when I finally got inside, smoke/steam was coming from my hood. I loosened the radiator cap like an idiot (I'm pretty inexperienced working on vehicles) and fluid shot out everywhere until I got the cap back on). Dumb question, but this does constitute an overheating episode, right?

I let it cool down a bit, checked that the fan was spinning, and when I started her up again, I noticed the temp gauge was in the middle of "Normal" (though it starts way left, and may be way off). On the drive home, I got up enough speed to cool it down a bit. That's been the situation ever since... if I'm driving over 40 mph, say, the temp creeps up and levels out. If I sit in traffic, it starts creeping up again.

I have a fair amount of slop in my belts, even after trying to tighten them. Not really sure if my fan clutch is working. Never heard the "jet take-off" sound (it seems plenty loud under normal conditions), but do have a bit of resistance when I try to spin the fan when the truck is off/cold.

Again, I'm an idiot, but draining and replacing coolant is the one highly recommended job I have yet to do since owning the truck (been too busy replacing the glow plugs, injector return lines, fuel filter/water separator, tires, u joints, calipers, etc. etc.). Except for the boil-off, and increasing amounts in the reservoir, the coolant level has stayed consistent. Can't really tell if the radiator/water pump is working, though. No visible "flow" through rad. fill hole, but not sure what I should be seeing. If I leave the cap off, it will eventually belch out fluid. Everything gets hot as hell if I leave it idling, but the big upper hose doesn't seem as hot as the little return(?) lines. Neither upper or lower hose seems to be collapsing.

I have bought the proper replacement thermostat (Motorcraft E5TZ-8575-C), but not installed it yet. I have 4 gallons of Napa green, 4 gallons of distilled water, and 2 bottles of Napa Kool, but waiting to see whether radiator is shot or what before I drain and replace. Still can't find the block drain holes for the life of me. Engine is dirty and black as hell, but I think that's from the old return line leaks.

Any tips on how to start diagnosing? Which order of replacement/repair? I have 20 days left til inspection, and would like it done before then.

For what it's worth, there was clearly an major overheat at some point in this truck's past, as the fan shroud is melted and cracked at the top. Also, the radiator has an odd little "smaller radiator" section in front. Is this stock?

Thanks a million in advance.

 

It's your thermostat. It's probably jammed itself shut.
I had an actual temp gauge, and I actually drove a good 50-100 miles with the darned thing stuck shut and never got over 220. 'Course, I was empty, and driving highway speeds(so lots of airflow), but...

I threw a cheapy thermostat in mine, though... and it solved the problem entirely. Now, I can watch my thermostat opening and closing; even with a 6+K trailer on, it still cycles open and shut when cruising. Obviously, going up hills with that made it warm up beyond that point, but...

Our engines are amazing at not putting out a ton of heat, especially at idle/low throttle positions.

Edit:
I'd just go the simple route for now -- Grab a 5-gal bucket, pop the bottom radiator hose, pull the radiator cap. drain as much as you can easily, then pull the thermostat.
You'll need to remove the alternator and the vacuum pump while doing so. It's about a 2-hour job, if you have tools handy.
Replace with your current coolant, or use some new... not that it'll matter much.

 

Thanks for the feedback, Macrobb. Much appreciated.

I'll report back when I have the new thermostat in.

Out of curiosity, if I wanted to throw a new temp guage in, where would I plumb it into the system? Thanks.

 

I'm thinking to add a temperature gauge, whats the best way to plumb one in, a new one?

 

I have come to feel many stock pressure and temperature gauges in American trucks are suspect, one way or another. One can simply buy a quality after market gauge and sender.

Isspro, VDO, and Auto Meter would be my choice.

Also, a non-contact IR hand-held temperature gauge is a darn handy item when diagnosing: is the motor really over heating, is my radiator plugged, is the t-stat opening?

 

BTW, Isspro is having a "Garage Sale":

ISSPRO.com - Quality Gauges, Tachometers, Speedometers and more!

 

Drivers side head. Two ports, one in front, the other towards the back. The front port has the over-temp light sensor in it, the rear just has a plug. I like to use the rear one myself as to keep the factory equipment working, but many don't like fighting the rear pug and just opt to pull the over-temp sensor.

 

just a word of advice. if you change the thermostat, only use one purchased from ford or international. aftermarket t-stats have been known to not work properly in our engines, and overheat them.

 

On the other hand, that is anecdotal experience -- One I picked up from car quest keeps things cooler than factory under light load; right at the 190F mark, and even under heavy load, it does a great job of allowing good flow.

The Chinese ones are more likely to break, being potentially of shoddy quality... But all the examples I've seen of this involve it breaking /open/(due to how the spring is designed), meaning that if it fails your truck just won't get warm quickly(versus overheating).

 

i have seen hundreds of stant t-stats installed in our engines that then overheat and get towed into the shop. every single time it was a direct result of the "new" t-stat not opening. replace it with either a ford or international unit and send it out on it's way.

my local ford dealer even learned the hard way. they had to replace an engine because they used a stant t-stat in it and melted the engine because the tech started it and walked away. it overheated in the services bays and did not shut off until it heat seized.

 

I just replaced an after market thermostat with a motorcraft and all is good now.