Afternoon y'all,
First post here, though I have used the forum to help solve problems on several trucks over the years.

My current problem I have seen addressed here, but never with firm solutions.

Recently acquired a 2001 350, 4x4, 7.3, 4R100, 230k miles. Recent receipts- rebuilt transmission 15k miles ago, (replaced the almost new solenoid shortly after), newer turbo, injectors, glow plugs and other misc receipts. The transmission rebuild included a new torque converter, new rebuild kit, solenoid and cleaning, but not replacing valve bodies.

Then the solenoid failed shortly after the rebuild, there was a note from the shop about the batteries testing low, and that potentially being related. The batteries were not changed until I purchased the truck. It would occasionally shift hard from 2nd to 3rd, but otherwise no issues in normal driving, or towing my 2k# flatbed.

I used it to tow my 28’ bumper pull (5300# dry) and the transmission started getting warm on the first 75 mile trip (never over 220). I installed a 6.0 cooler and put about another 100 miles without over heating towing the camper before heading on a 1400 mile road trip.

On the trip, the transmission started warming up again. I tried a stretch with overdrive off @ 55mph and it quickly heated up. After stopping and letting it cool, I got it up to 70mph in OD and it never got over 190* the rest of the drive. I don’t believe the TC is locking up in 3rd. I have yet to have any codes/flashing OD light.

I am waiting on my FORScan dongle to ship, but am curious if anyone has any insight. Would a bad solenoid cause the issue in 3rd? Would bad batteries cause the solenoid to fail?

My next plan is to drop the pan and replace filter/fluid and inspect for clutch/other debris in the fluid. Debating replacing solenoid at the same time.

 

A couple other notes-
- Fluid was bright red, free of debris, slight burnt smell but not terrible, when I swapped the cooler to the 6.0.
- I did not bypass the radiator when installing the 6.0 cooler.
- bypass tube is still in place

 

Now I'm trying to think if my `99 locks the converter clutch when at speed and low load with overdrive locked out. I usually notice this kind of thing, but can't say I've noticed this particular combination locking the converter or given much thought. I'll have to pay attention next time I drive it.

I'm curious how hot it got while towing in 3/unlocked?

Either way, you should be good towing with overdrive.

 

From the time I turned overdrive off, to pulling off the highway was about 10-12 miles, and it climbed from 180 to 220+ before I pulled off.

I agree, I can tow in OD. But for work and cross country travel, I need to be able to reliably pull 4000+ pounds. I have been known to do questionable things re: my definition of reliable, but for this truck and my needs, I wouldn’t trust consistently towing with 75% of its intended gears. I need to be able to trust it fully, and currently I don’t.

 

I have an E4OD and use the larger 6.0 cooler. On the hottest days up the steepest passes, I have never seen the temp go above 190. Normal driving [towing a 10k, 5th wheel] it hovers around 150F. My engine lacks power and I believe in 2nd gear, the converter is not locked [towing uphill, almost full throttle]. At that extreme load, it's never more than 190F.

I would get a pressure gauge. For me, I purchased a gauge that has pressure and temperature. That way, I don't need an extra gauge. I like gauges, but there comes a time where too much information just makes me worried. Ignorance is bliss.

With a pressure gauge, you will know real quick when you are in limp home mode.

Google normal automatic fluid temperature range. 220F is within the normal range. You and I may not like that, but it's within the normal range. Synthetic fluid can survive higher temperatures before they start to fail.

I believe in the temperature bypass bolted to the side of the transmission, but if that is leaking internally, all the fluid is not being sent to the cooler. They are fairly cheap but they also can be rebuilt. Some shops think that bypassing them is a good idea. I do not share that opinion.