I have a 1990 f250 diesel (7.3 IDI non turbo) 4x4 4:11 rear axle 158k miles.
the tranny occasionally overheats when on the high way over 70mph for an extended period of time or when under heavy loads for a while.
First time on the highway, second time was after all day of hauling 7-10k pound trailer of manure to the field, looked back and saw some smoke from the tranny, took it easy for a little bit and then back to it no more problems for the rest of the day. After research I found out the original cooler is undersized so I ordered a new bigger one and turns out it’s the same as what’s in it, so apparently it already has the bigger cooler in it.
Is there something else that’s causing it to run warmer than it should be or am I simply overworking it?
there are no others issues with it, shifts fine and just changed the fluid and filter.

thanks in advance

 

Three questions:

1. Are you towing in OD?
2. What did the tranny fluid look and smell like when you dropped the filter?
3. Is this the original transmission, as far as you know?

 

Define hot. Do you have a temperature gauge? If not, is it just possible that you may have a small trans leak that drips on the exhaust?

 

Yeah it's gunna get hot with those gears at that speed.

 

no I don’t think so, was only driving a mile away to dump and refill, barely got to 4th gear. If you’re referring to the overdrive button on the dash I didn’t touch that at all.
fluid didn’t smell or look unusual to me, it had a little bit of dark sludge in the bottom of the pan but I didn’t think it was anything to be concerned about.
and yes original tranny as far as I know.

Please excuse my lack of knowledge, I’m not very familiar with how auto transmissions work, I’ve never worked with them before.

 

I do not have a temp gauge on it but I plan to put one on soon.
I’ve checked for leaks and there are no other leaks. Trans is completely dry until it overheats.

 

Overheating auto transmissions (that arent actively slipping) are usually caused by damaged or clogged transmissions cooler lines.

 

I forgot to mention I’ve made multiple 3-4 hour trips on the highway since then staying right at 70 and no issue whatsoever.

 

that never occurred to me, I’ll check that out thanks

 

It’s possible it over heated, the front seal went temporarily soft, it pumped out some fluid, relieved it’s pressure - ie. fluid was pushed out the front seal of the pump at the torque converter - then when it cools back off it seals up again properly. It may be time to change out that seal, and use a Viton seal when it replaced. Any transmission or good auto shop should be able to do this.

You’re cooler may be old and partially plugged up. It may be worth swapping in the new one and trying. I would also instal a trans temp gauge, even if just temporary to see what temps you have before swapping in the new cooler, so you have a base line.

The temp probe can be installed in the rh side of the transmission. There is a small plug for a pressure test port. Just make sure the probe is not too long to fit in it. Use a small pick or screw drive to test the depth of the port and compare it to your gauge’s probe. Should be lots of threads with pics of it, if not post up, someone can get you picture.

For coolers, Trucooll makes nice units. Larger than the factory stock, and has an option for a Thermo couple to restrict flow in cold weather. Alternatively, the best is probably the Ford 6.0 transmission cooler, you can probably order one online, or rock auto.

 

very helpful thank you very much!

 

Hey sorry, typo. The pressure test port is on LH side of the trans… just ahead of the TRS (MLPS).

 

How hot is it getting?

 

I got a temp gauge installed. Cruising at 60mph it’s around 170-180, at 70mph empty it’s about 210,
and hauling a 2,000# trailer at 70-75 it’s stays around 220. Is this acceptable temperature ranges or is it hotter than it should be?

 

Get a nice big transmission cooler. Bypass the radiator all together and only run through the transmission cooler. And run it right in front of everything so it get lots of wind. One of the nice ones with the AN fittings. Doesn't have to be Mishimoto. And try get it as big as possible. And some high quality fluid. Maybe do the engine coolant at the same time. See if you drop down to 10⁰ below engine operating temp while loaded. That's upper end temps but not insane.