I strongly disagree with this. The radiator cooler removes a lot more heat than the aux cooler can remove. You'll lose a lot of trans cooling by skipping the radiator cooler.

 

I don't mean just a Hayes auxiliary. Something heavier duty. You can go in series and do both. I prefer to not run through my radiators.

 

Seems on the warmer side for lightly loaded, imo. Your coolers may be dirty and restricted, try giving them a good cleaning - bugs and dirt can really plug them up. You can also have a look into the Trucool coolers and the 6.0 powerstroke cooler.

Trucool has a Thermo bypass for cold weather if that applies to you. The 6.0 cooler is much larger. Run it through the radiator cooler first, don’t skip that.

I used the Tru-Cool with the Thermo bypass. In the end I didn’t use the Thermo bypass, I’m not running it in cold weather on the highways anymore. Personally I’ll use the 6.0 cooler in the future.

 

The 170-180 is ideal trans temps (w/ sending unit @ test port). In a perfect world, your trans would run right there 100% of the time.
210-220 is still very safe. If you want to try to keep ideal temps most of the time, you can install Tru-cool Aux Cooler LPD47391 & bypass/T-stat. This is what I use in both of my work trucks and I see ideal trans temps the majority of the time.

Be sure your aux cooler is after the radiator.


This question implies that one shouldn't tow in OD with the E4OD. This isn't the case. It's built 100% for towing in OD.
The ZF5 manual trans, is the trans that Ford states not to tow in OD with.

For sure. Not to mention the high risk of burning the trans up in traffic jams, plowing, off road, or idling.


I suspect this also, however it's probably just an aged seal that needs to be changed. According to the temps posted, I bet it takes just getting warm, but if happens again, he'll know if it actually runs hot now. Well above his posted max 220F so far.

 

the only reason to not use OD is when you are are in situations where your truck will kick down into 3rd and reupshift
That constant shifting creates heat and wear, and if its happening, staying in 3rd is adviseable

but if you can go in 4th and not do that, then by all means

 

Damn sure use both coolers
Last I heard, Fords strategy was to cut out OD if the vehicle overheats
I believe your 1990 E4OD has no FLT / TFT sensor so it's up to you to keep it OUT of overdrive when towing a heavy load
Get an actual mechanical coolant temperature gauge on it, is what I'd do, and watch it closely
Once you determine exactly how hot your engine is getting, you can make a decent decision on what to do, or whether you have an actual problem or not
Fords strategy is to keep the coolant and the trans fluid / engine oil all the same temp
If they can keep the engine oil the same temperature as the coolant, your engine will last longer
If they can keep your transmission fluid the same temperature as the coolant your trans will last longer

 

Gear hunting in the diesel (like the op has) engine isn't much of a concern. They tend to enter OD and hang out there, unless they need to downshift for hills. That's more a concern with the 302 engine than most others.
Cancelling OD wont make the trans run cooler than in OD. Either way, the converter will be locked and the pump is flowing large amounts of fluid when the converter locks (especially with the '95+ pumps). You'll never see a temp gauge drop (w/ sender @ test port) by canceling OD. You'll simply be burning more fuel, using a lower gear. There's been many myths about OD in the E4OD over the years for whatever reasons, but the fact is, it should be treated as just another gear. It's not more prone to heat than any other gear. The most prone gears to heat would be 1-3 in conditions (primarily, but not limited to; vehicle speed) where the converter isn't locked. One could argue, the best gear to run the coolest will be in OD; due to having a locked converter and vehicle speed that is sending large amount of airflow through the coolers. If you're not running 200F or below in OD, you need to ensure the trans lines are free flowing and or install a larger aux cooler.

On both of my work trucks w/ E4OD's, I have:
Temp gauges w/ sender @ test port.
1995 front pumps.
4r100 bypass w/ upgraded 3/8 lines.
Tru-cool Aux Cooler LPD47391 w/tru-cool thermal bypass.
(tugger shift kits and extra low stall converters, but these are not primary cooling upgrades.)

Outside of July and August where I may see 200-210 trans temps from time to time (with is great.) they run 180F (which is near perfect) once up to temp all other months, like 95% of the time, if not 99%. If I cancel OD, it's probably because I'm going down a steep grade.

 

my trans puking from low load not towing just driving became from my restricted cooler line in a kink near the radiator on the lower line, larger diameter would have been good factory to mitigate this, but i also had restriction on the cooler but i was able to clear that, but the rusty fitting/line failed before it could release while i tried to work it ol, so I bypassed, but now it doesnt warm up. i have a cracked end tank anyway, so i eventually i will fix it right but id probably get the 4r100 bypass, put a new spring kit in it , and then get larger diameter and use the same time to properly plumb my aux cooler


here i cut it the first time as far high as possible , but then i couldnt get a flare tool on

plus a flare tool wouldnt play nice with this being partially folded

I cut it a bit further so I could have a more round pipe and reach it from below AND get the flare so I could put a simple flare on , to encourage my hose repair to stay

The line uses is sunsong trans cooler line, which is fantastic very durable and stiff (less likely to kink, more abrasive protection) and two fuel injection clamps , opposed to each other

This hose combined with the clamps done this way, would have worked without a flare

But it gets quite cold here, and Id like to minimize my chances of it popping off in cold one day and losing my trans fluid quickly especially being sprayed near the fan lol. messy. Simple flare , it was. but in a situation where you have a short bit of pipe rusted out or pinched, you could safely bridge the pipe with this method and using 4 clamps between a section, youd very unlikely pop it off. just a cool trick might help someone. same situation as PS return lines

 

I wrote that up wrong
Mechanics error
It is converter lockup that is denied in an overheat situation, not 4th gear
That'll work AuroraGirl

 

Liquid to liquid sheds more BTU's than liquid to air, by a very large margin.