Hi All,
I have a '98 XJ 4.0 with the AW4 and factory transmission cooler. I'm soon going to be repairing the lines from the transmission to the radiator. Whilst they're off, I want to flush the radiator and transmission cooler to make sure they're flowing freely.

Can anybody guide me on the best way to do this?

 

What I do is disconnect the rearmost transmission cooler hard line where it returns to the transmission. I put a short piece of tubing over the end of the metal line and run the engine while the fluid flows through the transmission and cooler. Shut it off as soon as you see any bubbles, then refill and repeat a couple of times.

EDIT: In rereading your post, I see you're planning replace the lines and are likely trying to flush the cooler separately. Do you have access to compressed air? If so, I'd probably just blow it out with that in both directions. Just don't crank up the pressure too high if it's not flowing well.

 

Obviously this was easier cause I added one to my '00 and cleaned it before I did but thinking just get
a can of that Kooler Kleen, find a brake line that will screw into the end of the hose on that, get a clamp,
and shove it in to the line after you disconnect it.
Disconnect the other line and shove the hose in a drain pain.
I would tell you what size brake line I used but damned if I remember.
I'm guessing you could pull this off while in the Jeep.

 

^This is the best way. But I would just use a couple cans of brake cleaner and an air compressor to blow it through.

 

Disconnect the cooler lines at the transmission. Use a hand transfer pump with clear vinyl hose. Push fresh fluid in one line until it runs clean out the other. Use only ATF+4. You can backflush by swapping which line you push into. Finish by blowing compressed air through to clear any leftover fluid.

 

AW4's love Dexron-III/Mercon fluid and it has detergent properties. Flushing any part of the system with another fluid could contaminate the Dexron-III/Mercon and lead to damaging your transmission. Lube&Tune shops that have hard sold transmission flushes with other fluids have been sued for damaging their costumer's cars.

 

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Thank you all, this is super helpful. I'm performing this flush to make sure the cooler isn't blocked, not to perform a fluid change (although that will be happening at the same time).

I've had some transmission issues for a while that only happen when the transmission is hot, so I want to make sure I've done everything I can to ensure it cools properly.

 

Sounds like a plan. If your transmission troubles persist, it may be time to check the solenoids. They tend to act up more when hot when on their way out.

 

Yeah, that's along the lines of what I've been investigating. It's a whole story, but my lock-up torque converter doesn't work when hot. I replaced the solenoid a year ago and it fixed it for a while, but the problem came back pretty quickly.

 

Could be the lockup in the torque converter itself. Unpopular opinion would be to just get a low mileage salvage trans, a new torque converter and be done with it.