The dinky radiator is the weak link in the XJ cooling system chain of components and is why all of the XJ cooling system components must be functioning at 100% efficiency to prevent overheating in 90*+ ambient temps.

To prove this, the XJ rad core is something like 1.27 sq. inches frontal surface area per engine cubic inch displacement. On our other vehicles (including 2 wheelers), their rads sq. inches frontal surface area per engine cubic inch displacement range from 2 to 3 sq. inches frontal surface area per engine cubic inch displacement. I believe the 4.0L rads in Wranglers and Grand Cherokees have a larger radiator sq. inch frontal surface area per engine cubic inch displacement ratio than the XJ rad (same motor, bigger radiator).

Bottom line, in order for the rad to "fit" in the XJ, the XJ rad has to be dinky in size.

 

And this is due to the vehicle not being designed for this engine in mind I'd guess. Use to have only a 4cyl and V6.

It'd be interesting to do a temp comparison using the same XJ with then w/o the a/c condensor. That condensor's fairly dense.

 

I don't think whether the condenser is there or not or it's density would make much difference in engine coolant temp. The fact that the condenser gets hotter than heck with a/c use would make the big difference, since that condenser heat passes thru the rad.

 

That's true.

Bottom line is you've just got to keep these cooling systems in top shape. More so than any other vehicle I've owned I'll admit.

 

I don't have any actual numbers available, but unless the designers were completely clueless, the system is set up so that the transmission gets cooled by the transmission cooler. That means it's normally coming into the radiator ABOVE normal engine coolant temperature. The whole point of a radiator trans cooler is that it will extract heat from the transmission fluid.

To put it another way, the system is designed to dump heat from the transmission into the engine coolant, and from there (we hope) into the air passing through the radiator. If you are towing, there's more heat to dump into your engine coolant.

If you are already overheating, that's the last thing you want. Especially since, as already pointed out, our rads are not exactly oversize.

If you put the trans cooler AFTER the radiator, your engine cooling system takes most of the heat out of the transmission, then passes it to the trans cooler to chill it down even more. You are asking your engine cooling system to do the heavy lifting.

 

Since u stated u don't have any actual numbers.........I would bet just the opposite is true for the designers/engineers and say that they have all kinds of numbers from testing under all kinds of driving conditions......so, who is really clueless here? Something tells me, but for sure, that the designers/engineers probably tested the optional secondary auxiliary tranny cooler both ahead of and after the primary internal radiator mounted tranny cooler. From there, my guess is, their tests determined that having the auxiliary cooler in-line with and AFTER (the rad cooler) was the best for max tranny fluid cooling.

The instructions that come with the B&M #70264 say "for max cooling, mount their auxiliary tranny fluid cooler in-line with and after the primary (rad mounted) tranny fluid cooler".........just like the factory mounts their OE optional auxiliary tranny fluid cooler. Hummm. The factory also mounts the optional secondary auxiliary tranny cooler between the condenser and grille for max air flow thru the auxiliary cooler, thus allowing for max tranny fluid cooling. My guess is, but for sure, that's why B&M recommends their auxiliary tranny cooler be mounted between the condenser and grille as well.......in max air flow for max tranny fluid cooling.

I'm not going to make any claims about AW4 tranny fluid temps because I have been unable to program our ScanGauge to display tranny fluid temps. My guess is, it's something to do with the XJ protocol not supporting/providing tranny fluid temps to the ScanGauge. Since the towing we do with our XJ is 2K-2.5K lbs max, usually less, I'm not concerned with tranny fluid temps in the XJ.....especially since we have changed the tranny filter and have done several tranny fluid dumps/refills. I'm also not concerned about XJ tranny fluid temps because we have installed a secondary auxiliary tranny cooler (B&M #70264) mounted identically (both fluid flow and cooler location) to the way the optional factory installed auxiliary tranny cooler is mounted.

Again, no tranny temp gauge in our XJ BUT, we do have ScanGauges displaying tranny fluid temps in both of our other 2 vehicles, 'yota RAV4 and GMC Canyon. U made a statement something to the effect "That means it's (tranny fluid) normally coming into the radiator ABOVE normal engine coolant temperature". My question to u is.....have u actually observed that tranny fluid entering the radiator (cooler) is above normal engine coolant temps?

I have never observed the ScanGauge displaying tranny fluid temps above engine coolant temps in either our 'yota or GMC.....in fact, in 99% of our driving time/conditions, tranny fluid temps remain 20*-25* below engine coolant temps and that is right now, this time of year, already in 3 digit ambients, in town or on the Interstate. Both vehicles run/display 180*-190* engine coolant temps on the ScanGauge.

From what I have observed on the ScanGauges, tranny fluid is very slow to warm up.......even in the summer heat, it takes much longer for the tranny to warm up than the engine. In the winter months, tranny fluid temp displaying 90*-100* below engine coolant temp is quite common. That's why in another thread, I suggested a tranny fluid temp gauge that reads/displays below 100*.....if the gauge starts at 100*, it's not likely to display during cold weather driving.

That's what the ScanGauge shows in both of our other 2 vehicles and I'm going to go out on limb and say the AW4 tranny is probably not a whole lot different,.....but again, I'm clueless (just like the designers) as to being positive about how the AW4 performs.

 

FINALLY got to reading the instructions for the trans cooler. Of the 3 suggested mounting positions there's quite a difference in cooling efficiency. #1 being in front of both rad and a/c condensor,#2 in between the two,and #3 behind the two.

100%(#1) to 75%(#2) to 60%(#3).

 

.....and in addition to "where" to mount the cooler, I believe they (B&M) also suggest mounting it in-line with and after the factory cooler for max efficiency.

EZ, post up your cooler mount (with pics).

 

Yes they do.

I'm hoping to get in this week for a towing trip next weekend. Pics? Sure.
But they're going to look an awful lot like yours.

 

......but a lot newer.

 

Oh I'll make purrty all right.

 

My apologies to the OP.......kinda turned a "overheat" thread into a tranny cooler thread....sorry.

 

Let me try to help you. You are confusing two different issues.

The designers of the Jeep are one set of people with one set of design goals and constraints.

The designers of aftermarket trans coolers are a different set of people who have a different set of design goals and constraints.

The first group is trying to make sure the trans doesn't overheat, and that the engine doesn't overheat. They aren't trying to get max cooling for either one, just good enough. They are doing a balancing act. (By the way, that balancing act also includes making sure the trans is at proper operating temperature. Not too hot, and not too cold.)


The second group doesn't care about engine overheating. It's not their problem. They only care about max cooling for the trans.

That's after the radiator, of course.

They don't care one bit if the radiator takes the worst of the trans heat. It's not their problem. All they care about is max cooling for the trans.


Now, a bit about that basic thermodynamics. This one is pretty simple: Energy (heat) flows from higher levels to lower levels, never the other way around. The higher the difference , the faster the energy moves from one location to the other.

If your trans fluid is cooler than the engine coolant, going through the stock trans cooler will make the trans fluid HOTTER, not cooler. It will pick up heat from the engine coolant.

If the trans fluid is HOTTER than the engine coolant, it will transfer heat to the engine coolant and come out cooler than it went in. Probably not the same temp as the engine coolant, but at least cooler than it was.

Now drop it through an external trans cooler, and it will transfer more heat to the air. Where does that heat go? It depends where the trans cooler is. If it's in front of the radiator, It's going over the radiator. What happens next depends on the relative temperatures. If the air gets heated above the temp of engine coolant, it will transfer some more heat into your engine coolant. BEST CASE: The air is below the coolant temp, so it won't add heat, but it will still be hotter than ambient air, so that part of the radiator will get less cooling than if the external trans cooler were not there.


Now, unless your engine is radically overheated, the engine coolant temp will cool the trans fluid within the design limits of the transmission. Making this the last cooling stop does no harm to the transmission. It's not the best possible cooling, but it's good enough. Obviously, since that's exactly what the factory does. When you add the aftermarket trans cooler BEFORE the stock trans cooler, you dump heat out BEFORE the radiator, thus you don't add that heat to your engine. In fact, you might wind up extracting heat from your engine. In a vehicle with a marginal cooling system, that's a good thing.

When you put the aftermarket trans cooler after the stock trans cooler, you get a cooler transmission, but you also get a hotter engine. How cool is the transmission? Cooler than the factory "good enough" level. Is that a big benefit? No. It's a small benefit. It doesn't really buy you much.

Putting it BEFORE the stock cooler buys you a cooler engine, and the factory "good enough" cooling for the trans.

So, if you want max cooling for the trans, and you don't care about engine heat, you put it after.

If you do care about engine heat, and are happy with "good enough for the factory" cooling for the trans, you put it before.

Understanding beats blindly following directions, every day.

 

Again, to the OP, please accept the apology for the hi-jack.

FWIW, here is a little more info that disagrees with our resident designer/engineer/cooling expert. (he does know how to correctly spell duh)

http://www.trucool.com/?q=frequently-asked-questions

 

I hear all these stories about needing extra cooling than what came from the factory. At 250,000 miles I towed a 6x12 double axle enclosed trailer 1500 miles in August heat, uphill all the way from Tennessee to Colorado. Most all interstate locked in 3rd. I don't ever remember the engine temp rising. And when I changed my trans fluid it was still nice and red. The same cooling system can handle I-8 between El Centro and San Diego (desert and grades significant enough Caltrans puts radiator water drums every 1/2 mile). All original factory parts except the thermostat which I change every couple of years using one from the dealer.

Copper and brass radiators... Do they work as effectively as aluminum? Change the thermostat with a dealer one. The jiggle pin goes on top. Correct engine temperature is 210F. It should not cycle. That's almost certainly a bad thermostat. When your coolant temp is too low engine wear increases. It's pretty significant. I think every 20-30F is 2-4X increase in wear.

Temperature creep sitting in traffic is usually a fan clutch or radiator efficiency problem or both.

When everything else checks out don't rule out a problem with the engine head or head gasket. Erratic temperatures can be direct engine problems, not cooling systems.