Kymasabe

OK, here it is: '04 WJ, 2WD, with I think 42RE transmission.
When i got the Jeep a couple of years ago, previous owner had bypassed the trans cooler in the radiator and was running aftermarket cooler mounted behind the grill. This past summer, I replaced the radiator and did not hook up the trans cooler in the radiator, left everything as-is. But, I have a long drive/trip coming up in a couple months and thinking I want as much cooling ability as possible so would like to run both coolers. Here's are my questions/problems:
1. my cooler lines were cut back and are mostly hose now. Which line from the trans is feed and return? I think I read somewhere that the forward line is feed, and return goes to a fitting further back on the transmission?
2. I'm guessing I go into the radiator cooler first, but do I feed into the top or the bottom of the trans cooler in the radiator?
3. I guess once I leave the cooler in the radiator, I feed in and out of the aftermarket cooler in same order that I did on radiator cooler?
4. I intend to drop my pan and do a service at same time, I have new Dorman pan with drain plug and new Mopar reusable gasket. I'll pick up a filter at my local Napa, any idea how much ATF+4 I'm gonna need ?
5. Last question and possibly the hardest to answer...ANY idea what size fittings I'm going to need to screw into the cooler ports in the radiator?
6. I lied...one more question I just thought of. Do I need to tighten/adjust bans when I do a trans service? IF so...how?
Help !!

dave1123

Okay, here's my input on how to plumb the coolers.

The radiator cooler does double duty in that in cold weather it warms the trans so that it functions properly sooner. There is a thermistor in the trans that won't allow it to shift into 4th (O/D) until it reaches 32*F. It also kicks it out of O/D if it's over 240*F.

In hot weather you need an aux cooler to reduce the fluid temp to keep it from overheating. You should send the hot fluid thru the aux cooler first to reduce it's temp so that it doesn't overheat the engine's cooling system.

The line coming out of the forward part of the trans carries hot fluid from the converter and the rear one returns to the pan. Unless there is a blockage, the most pressure you'll find in those lines is about 40 psi so you can use rubber hose and good clamps with bubble ends on the tubes to prevent them sliding off. You only need flexible hose anywhere there is motion between the engine/trans and the frame/radiator/cooler, like near the drive belts. The hot fluid should enter the bottom fitting so as to eliminate the possibility of air pockets in the system, but it really doesn't matter.

You'll need around 6 quarts of ATF+4 PLUS any additional capacity of the Dorman pan. Make sure you get the filter for the 2wd. I think there's a difference with the 4wd one.

My 42re has 230K miles on it and I've never adjusted the bands. It still shifts solidly and on time.

IDK about the tube fittings because I've never had to replace them. I'm thinking 3/8 flare tube?

Kymasabe

I forgot to mention, I'm in SW Florida so it doesn't take much to warm the trans, my concern is max cooling ability.

dave1123

Well, I guess you answered your own question then, didn't ya?

Kymasabe

Not really.
I'm still under the impression that the cooler in the radiator will still cool the trans fluid, and was thinking that adding an aftermarket one after that would drop temps even lower.
I still not clear if that's the order that would provide the most cooling, or if I should skip the cooler in the rad and just get a bigger, better aftermarket cooler or something like an Explorer trans cooler form the junk yard?

dave1123

Well, you've got to remember the radiator will remain just below normal operating temp determined by the thermostat. You can use an infrared thermometer, but I think the coolant temp coming out of the radiator is about 160*F and going in is at around 195-210*F.

Given your location, I'd just use a large aux cooler in front of the radiator and forget using the rad cooler. I've seen a custom street rod using just a pair of small power steering coolers hung below the radiator. He said he wanted to hide them, but I thought they should have been in the fan's airstream.

Most of the heat in an automatic transmission is generated in the torque converter by fluid slippage. Sitting still in gear or pulling a load is when you get the most heat.

Of course, these are MY opinions and you should do whatever floats your boat!