I have a medium sized transmission cooler in front of the radiator, but want to add more cooling as I have really big tires, and do a lot of slow crawling in my 1990 XJ. My transmission can get warm. I can add a bigger or second cooler in front of radiator, but I dont want to harm the engine cooling, as she tends to sometimes run on the hot side on slow steep trails in hot weather as it is.
What about adding a cooler with electric fan under the floor? I think it can be placed just ahead of the rear axle perhaps, looks like there is room. I dont see many folks do this, so I wonder if that is cause it is a bad idea or???

I have mounted engine oil coolers for VWs and Porsches like this, and it works nice, the key being having a good electric fan and shroud.

Thanks!

I believe the AW4 only sends part of the fluid through the cooler, not all of it. At some point, as you add more and more hose and cooler to the circuit, the backpressure will reduce the flow. No clue where this crossover occurs, just thinking out loud. Other than that, if you keep everything protected, mounting it in the rear would work just fine.

DO NOT bypass the radiator. If you have a gauge, you can try it, but you'll quickly reconnect it...

I assume you have a switch to manually turn on the electric cooling fan. The autometer gauge I'm using has an output that I drive a relay with to turn on the fan when the temp gets too high, It has a warning light that comes on at 260F and I've only had it come on twice after towing a 24' pontoon boat up and over a big hill and then pretty much straight up the side of another one using a rutted dirt driveway. I think you'll be hard pressed to abuse a AW4 much worse than I have... :-) In the spring and fall, it stayed below 240F. The hottest week of the summer, 250F, 255F, ... I have a switch to turn on the fan, which I engage before I start that driveway. B&M 70268 cooler dead center in the middle. I presume you're using a plate-style cooler... There's a bigger model that "should" fit but I haven't tried.

With the basic wiring system on the Renix models, I'd be tempted to clear out the space there on the passenger's side and vent a cooler up through the hood. I have the later-model washer reservoir in the fender and an aftermarket coolant tank on the driver's side of my '88 XJ. There "should" be enough room there for a fan on the cooler.

I'm not sure what your aesthetic requirements are, but mounting a fan on a cooler in front of the radiator would kill two birds with one stone...

why is that? I've been setup bypassed for years without issue?

The cold side of the radiator has to be cooler than 200F, otherwise there's no way your engine would only be operating at 220F. Fluid-to-fluid coolers are much, much more efficient than fluid-to-air coolers, so even if it was 200F in the cold side of the radiator, it's still cooling the trans fluid if it's running hot. I've heard numbers as low as 160F in the cold side tank.

Upon find a strawberry milkshake in my transmission one day, I too bypassed the radiator and used only the B&M 70268 cooler. Ran it that way for a year. The following year, I installed a high end B&M gauge and found that it was running entirely too hot. It's been a number of years now so I'm a bit short on details, but it was significant, I remember it being an "oh crap, I better fix this" kind of thing with a very hard "Nope, not doing that again" lesson learned...

lengthy thread on the Oz forum (especially as trans cooler is on the hot side of the radiator for RHD)

Its to do with the laws of thermodynamics, as the previous poster alluded to

I did bypass mine for a while, with a temp gauge fitted, and it did not lower temps at all, appeared to run somewhat hotter

LHD & RHD rads - another one of the world's great mysteries!

Adding an additional transmission cooler with an electric fan under the floor of your 1990 XJ could be a viable solution to address transmission overheating during slow, off-road crawling.


What trans temps are you seeing that is making you want more cooling?

I run a B&M cooler in front of the radiator offset to the e-fan side. I also have an override switch on the fan which I typically keep on while wheeling, so the trans cooler gets a fair amount of air through it.

When I mounted my temp gauge, I put it on the cold side thinking that I'd rather see the fluid temp being supplied to the trans rather than coming out. Not sure if that was the best idea. It was awhile ago and I'm not changing it. I rarely see more than ~160°F on my gauge. That's with 3.55's, 35's, and max ambient temps around 95°F with high humidity.