fivenote

I got the B&M 70268. Same as the OP. They're $55 at Amazon. The extra hose, clamps and 3/8 connectors came out to another $15.

webejeepin

Subscribed. It's a very good question on temps in the winter time...was thinking the same.

I tool like to follow this, and find it interesting.

Perhaspe a few things that may help...Aeroforce Interceptor Scan Guage to monitor the tranny temp then add a 'winter front' which is a insulated 'pad' you can put on the front of your grill to limit the amout of direct air into the rad(s).
Get the type that has little flaps on them so you can control the amount of cold air intake. Just keep an eye on the scan guage....

mikesoffroad

I purchased a tranny cooler from the local Bumper to Bumper parts store. I wanted to get one that helped cool the tranny since I am running 37's and like to play on the rocks. The only problem is it is winter up here for 8 months of the year = lots of -30 weather. The unit that I was sold has a bypass in it that lets the thicker fluid (more viscocity) flow the shorter route. If the fluid gets thinner (less viscocity) then it flows throught all the fins to help cool. I hope I explained that correctly.

ronjenx

The stock cooler circuit in the 42RLE has a bypass, too. I have not been able find the bypass parameters, though.
So I don't know if it bypasses only if there is a total blockage in the cooler, or if it bypasses at a certain viscosity.

Suspector X

All that I have ever read about tranny operating temps from Hot Rod Mag to service manuals to everything in between have told that sump temps of 180ish is ideal.

I think we all agree that the fluid condition is one of the most important mechanical factors in tranny life and that's why 180 degrees is "settled" on. The hotter it's sustained temp, the sooner it needs changed but much cooler than 160ish (again an estimate) and you don't get hot enough to "burn off" moisture from within the fluid. To the best of my knowledge, the colder temps are not bad for the tranny it's self but bad for the fluid.

I always cool before the factory cooler to avoid over cooling since in theory the radiator could raise it up again if it is cold outside and it seems to work for me. I've used modest coolers on towing transmissions and when checked at the sump, mine have always stayed within +/- 10 degress what the radiator is running at the moment.

ronjenx

What you describe works fine for a trans cooler that is cooled by the water in the radiator. That's not the case with the JK. The stock cooler is outside of the radiator.

Like I've said before, the only reason 180°F is considered normal for the trans fluid is for a lot of years, the fluid was cooled by the 180° water, (or thereabouts).

I'm still researching if it's OK to have the trans temp remain as low as 90°-130°. Everything I've found so far indicates it's OK. Nothing official from transmission or transmission fluid engineers; just the opinions of people who work on transmissions a lot.
Still looking...

On mine, it's running fine. The fluid still looks like new.

Edit to add:

I just talked with tech support at Mobil, asking about Mobil ATF+4 transmission fluid.

I explained the following:
1. The JK trans cooler is outside the radiator.
2. The transmission is programmed to not allow torque converter lock-up until the fluid reached 80°F, which will reduce the time it takes to get to that temperature.
3. I have installed an additional transmission cooler.
4. My transmission fluid spends most of it's time in the 90°-130° range.

I then asked if that's too cool for the fluid.
The answer was no, that's fine; no reason to keep it higher.

I then called Valvoline Tech Support, and asked about their ATF+4, giving them the same info as above.
Their answer was not only is that temperature fine, "it's great that you can keep it that low".

So, I'm pretty sure it's not a problem. This winter will be interesting. I'll be watching the trans temp, and looking to see if it gets above 80°F.

fivenote

Great information! Thanks for hunting down the answers!

I just got back from my first long drive after installing the cooler last night. I averaged around 150, peaked at 170. This was 40 miles of highway and city traffic in 90 degree heat.

I'm hitting the beach with it in a few weeks. I'm curious what the temps will be then and later next winter.

If I haven't said it already, here it is again... this forum is tops!

Suspector X

Well at least I've learned that the JK cooler is not in the radiator so I guess trying to help was not a total loss.

fivenote

Don't feel bad... I just figured that out last night when I had the grill off to install the cooler. It looks like the factory cooler is the bottom quarter of the condenser in front of the radiator. You can see a solid metal line separating the top fins from the bottom. In all, it looks like a pretty small tranny cooler. It also looks like it's sitting below the grill and may not be getting much direct air.

I appreciated your comments. The thought of over-cooling in the winter has been in the back of my mind while doing this project, and I'm glad to see it discussed on the forum. I'm also counting on B&M's stacked plate design and "low pressure drop" that they say prevents over-cooling.

Suspector X

"Low pressure drop"? Is there a pressure level that needs to be maintained within a cooler or is it the volume that matters? I do know that the fluid can slow down a lot through a stacked plate type compared to a back and forth (am I saying that right?) type account of multiple parallel fluid paths.

After reading the same thing you saw I am even more confused about the low pressure drop thing. Is it a name for some feature? but I'm not sure what it does? Maybe it's the bypass feature that allows cold fluid to return to the pan? Idunno but I don't believe the cooling circuit is a high pressure circuit. Perhaps a real (ie paid) tranny expert could elaborate.