This is all I could come up with at the moment, an article by Four Wheeler magazine. They say the FSM states optimum temps are between 125-176F. (Third paragraph, last sentence)

http://www.fourwheeler.com/how-to/tr...ps-and-tricks/

 

We have a genuine '98 Jeep/Chrysler FSM.......not a Haynes, not a Chiltons. The AW4 section in the FSM is some 110 pages long. I have not read all 110 pages word for word but nowhere can I find the FSM saying anything about 125-176 tranny fluid temp range, like what is stated in the Four Wheeler Magazine article. Nowhere do I see in the FSM any reference to any fluid temp......high/low, good/bad. I may have missed it and I'm sure someone will be along to correct me if I did miss it. I wonder what FSM Four Wheeler Magazine got their info from.....don't think it is from the Jeep/Chrysler FSM.

There is a short section in the Jeep Cherokee FSM titled "Causes of Burnt Fluid" and it basically says burnt fluid is caused by overheating and then goes on to discuss what can cause tranny fluid overheating. No specific tranny fluid temp number or range is stated/referenced as being overheated.

There is also a short section in the FSM titled "Transmission Cooler" and in that section both the "main" cooler and optional "auxiliary" cooler r discussed, but with no reference of any kind to a specific tranny fluid "temp" and no reference to a fluid temp "range".

I see no reference anywhere to "heating/warming" tranny fluid, as in tranny fluid can be "too cold", but maybe I missed that as well.........however, I don't think so.

In that Four Wheeler Magazine article, is one of those gauges showing tranny fluid temp and the other gauge showing engine coolant temp, even though both gauges say "Trans"?

 

I'm pretty sure it's safe to say keep it under 200 degrees and you'll be fine.

 

.....but that's entirely different from the previous statement made earlier saying there's a "optimum temp range".

 

Under 175 would be better unless you are running synth fluid.
At some point cold fluid will change viscosity enough to drop out of spec and alter transmission operation.
I noticed it in the AW4 on below zero days, sluggish shifts until the fluid warmed. Exactly what that temperature is where operation is affected IDK, but there is one.

 

I don't think you will find this without contacting engineers at Aisin. Even then, they may not have any numbers to give you as this setup may have been arrived at by simple testing. Obviously the operating range of the AW4 is not critical or we'd have sensors on it.

****, even the engine - which does have critical temperature points - doesn't have the operating range called out in the FSM!

I suspect specs for the transmission amount to "not cold" as that is all the factory system can reliably deliver. Possibly the goal is just a certain viscosity of the fluid.

 

Bingo. Just because the number isn't stated explicitly, does NOT mean that there is not an optimum temperature range. I can't think of any complex machine that does NOT have an optimal temperature range.

The Field Service Manual is just that, a SERVICE manual. Since the temperature range is not adjustable, there's nothing to service, so there's really no reason to state it.

The design itself ensures that the trans remains in the optimal range if everything is working correctly. The engineers will have calculated normal operating temperatures, heat production rates, exchange rates, loss rates, etc., and sized the radiator cooler to keep the trans in the correct range.

In the olden days (when Cruiser & CCKen were young men), those numbers were calculated mostly by seat-of-the pants. Nowadays, it's complex computer modeling.

Damage from overheat is obvious and sometimes, immediate. Everybody recognizes it.

Damage from running too cool is probably a lot more subtle, likely only showing up as shortened lifespan. Nobody is EVER going to successfully lay responsibility for that at the feet of a trans cooler.

All the companies that sell coolers care about is making sure your trans is never too HOT, so they recommend putting it AFTER the rad cooler. That provides maximum cooling for the trans. It might not be the best thing for the trans, but it's definitely maximum cooling.

So, the trans cooler companies will always recommend putting the cooler after the rad cooler. That's what's in their best interests.

However, by putting an external trans cooler AFTER the rad cooler, you remove the system's ability to keep the trans warm enough.

On the other hand, if you put it BEFORE the rad cooler, you dump any excess heat from the trans, avoid putting that heat into your engine coolant, and retain the system's ability to keep the trans in the optimal range.

 

I'm not the one looking for any numbers because I know they don't exist. I forget now who made the statement in this thread saying there is a "optimum temp range" for tranny fluid. But hopefully they understand now there's no such animal or if there is, it's highly guarded and top secret.

Saying there's a "optimum temp range" for tranny fluid is kinda like saying 210* is the "optimum operating temp" for engine coolant.......how many times do we see that false post/statement?

The factory engineers (and tranny cooler mfgs.) have determined the best way to mount the auxiliary cooler is AFTER the primary cooler for 2 reasons......1. under cooling is a non-issue and 2. overheating is a major issue.

Can the auxiliary cooler be mounted ahead of the primary cooler?......sure. Is that the way the Factory mounts the auxiliary cooler and the cooler mfgs. recommend mounting the auxiliary?......nope. Only one person here recommends mounting the auxiliary cooler bass ackwards and for a reason (under cooling) that the Factory considers a non-issue.

 

Really? Where do you find that info?

 

U find it in the FSM.......have u not looked at a FSM diagram?.......the Factory mounted the auxiliary cooler in-line with and AFTER the primary cooler to provide max cooling as under-cooling is a non-issue. The aftermarket cooler instructions say to mount the auxiliary cooler AFTER the primary cooler for max cooling as under-cooling is a non-issue. The tranny warms up sufficiently, even in cold weather, just from driving. Again, under-cooling is a non-issue. If the tranny sees temps in which it is too cold to function, the motor probably won't start anyway.