Post radiator swap out stuff...

Just changed out the radiator for the first time in my '96 XJ 4.0 auto. Coolant emptied out of course but I was surprised that no transmission fluid came out when I disconnected the lines. Everythings back together now with the new radiator in, so filling and burping and refilling with coolant shouldn't be a problem...but I'm not so sure about the transmission fluid. Have I lost some trans fluid in the radiator that I'll have to top back up to get things right again?

Check the trans fluid level following the steps in your Service Manual, add more as required.

When I swapped radiators I don't recall a whole lot of trans fluid draining out. IIRC the trans/radiator heat interchanger is just a simple brass tube surrounded by engine coolant to allow the engine in assisting the trans getting up to temp; I'm not sure but I think it's only full when the trans pump is active/on.

If you're in a hot environment, this is a good time to bypass the radiator altogether and install a $20 transmission cooler.

Yes thanks for the advice.

First time hearing about this trans cooler. I'm in a semi hot environment...July and August can be upper 80s to 90s. Are there significant advantages to be had by transitioning to a trans cooler?

bradleyheathhays said:

Yes thanks for the advice.

First time hearing about this trans cooler. I'm in a semi hot environment...July and August can be upper 80s to 90s. Are there significant advantages to be had by transitioning to a trans cooler?

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I think most oem coolers come with factory towing. It's meant to keep the temperatures down in harsh driving conditions. Doesn't sound like you really need one. Doesn't hurt either. IMO helps extend the life of the transmission.

As I recall our oem cooler is relatively small.

For the new radiator I'd let it warm then check it like the good book says. If you didn't see much leak out , you probably don't have to add much in unless it's been leaking. Been over 6 years since I had to swap a XJ radiator, I don't recall if there were any leaks when pulled but then we have the coolers too. Just can't remember how all that hooked up.

Did a radiator swap on a sienna van, pita, bumper has to come off for access. That one leaked a good amount transmission fluid, took a couple of drives to finally get the radiator burped and transition fluid settled.

Comparatively the XJ is a cakewalk

bradleyheathhays said:

Yes thanks for the advice.

First time hearing about this trans cooler. I'm in a semi hot environment...July and August can be upper 80s to 90s. Are there significant advantages to be had by transitioning to a trans cooler?

Click to expand...

If your area max temp is in the 90s and you're not regularly towing a rig full of horses or whatever, just keep the stock setup. People in hot desert climates and who wheel/tow weight regularly will benefit from installing a transmission cooler. It's basically a small radiator dedicated purely to cooling transmission fluid.

The OEM/stock XJ transmission fluid/radiator loop isn't for cooling IIRC; it's actually to help warm up the trans fluid by exposing it to engine temps.

I tow a 4 wheeler on a golf cart trailer every now and then but other than that just regular driving. Sounds like I should just leave things as it. Good info though.

When the radiator heat exchanger is FULL, there is only about 1.5 cups of fluid in it, it's not under pressure, unless the motor is running, and most of it likely drains back out when the motor is turned off.

bradleyheathhays said:

......... Are there significant advantages to be had by transitioning to a trans cooler?

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On an XJ with the AW4 ... yes.

But fit a temp gauge to the gearbox and see whats going on - before leaping into, what maybe, unnescessary cooling changes.

ParadiseXJ said:

When the radiator heat exchanger is FULL, there is only about 1.5 cups of fluid in it, it's not under pressure, unless the motor is running, and most of it likely drains back out when the motor is turned off.

Click to expand...

Yep ... truly an insignificant little thing .. that does squat for "cooling"