Trans Cooler... has anyone experimented with....?

This is my '96 XJ, 4.0, AW4 I set-up as an Expedition Vehicle. Among many other mods, it has a RT Tent and weather proof surplus Viper Rocket Case mounted on a modified Conferr Rack. I've been racking my brain to find a solution to my A/T over heating when fully loaded and under a load, uphill, highway conditions.



Long story short, the previous owner had by-passed / abandoned the radiator trans cooler and installed a large cooler in front of the radiator. This seemed to works fine under normal loads, but under heavy loads, doesn't provide enough cooling for the tranny.

Obviously, the simple, common sense thing to do would be to plumb it back into the radiator cooler to solve the problem. BUT, and here's my dilemma, the radiator cooler is already in use as a water heater for my on-board hot water shower system, so I need to come up with another solution. Other than installing a second trans cooler with a thermostatically controlled fan, I was at a loss to come up with any other options until now. I'd like to get feedback on this idea, if anyone has every experimented with it, any drawbacks/ problems etc. anyone can see that would prevent it from working, I would appreciate any input / opinions.

I recently had to replace my heater control valve after it failed (blew apart) on a recent trip. That is how I slowly concocted this crazy idea.

What if.... :
1. .... I capped the radiator heater hoses.

2. .... I modified the heater core intake and outlets and ran the trans lines/fluid through them using the hot trans fluid as a heater heat source while at the same time dissipating (cooling) the trans fluid?

3. .... I also Modified the ducting system to be able to selectively divert the hot air from the core either inside or outside of the vehicle?

4. modified the ducting system again to divert (blow) cold air conditioned air over the heater core to add additional cooling power

5.... Installed a valved bypass loop before the core to bypass it all together** (and just use the external trans cooler), thus enabling the use of the air conditioning system for driver comfort when extra trans cooling is not necessary?
**(this would also ensure that if the core failed, I could by-pass it and not lose all of my trans "cooling capacity" or fluid)


Has anyone ever attempted this and if so, the results? Is it practical. Would it be efficient enough? Would the heater core stand up to the temps and/or pressure or the trans fluid? Most importantly, would it be a reliable alternative, at least for me?

To say the least, I'm thinking out of the box here :wow:. Any input would be appreciated.

SC

How about just a bigger/better cooler and/or its own small fan? Your what-if idea sounds retarded.

foxwar71 said:

How about just a bigger/better cooler and/or its own small fan? Your what-if idea sounds retarded.

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This is the kind of response that limits my participation in 's forums. Thanks. you're a credit to the organization.

I would like to experiment with an oil to fuel heat exchanger like what is used on turbine engines.

It just seems like you're trying to go thru a bunch of unnecessary complicated steps to fix a problem. The main part of the problem sounds to most likely be the cooler. How big is it? What style is it? Tube & fin or stacked plate? Instead of going thru all these weird steps, why not just address the problem directly?

Sounds like a lot of work when you could just get a better trans cooler with a fan and be done.

how much overheating? going uphill on interstate 8 in california on a 100+ degree day my XJ was loaded to the brim, i kept a steady 35-40mph the whole climb up the mountains and was holding a bit above 220. i had 33s and 4.56 gears, all good condition cooling components and a small extra tranny cooler. i wouldnt call that overheating.

are you geared? if not, thats your problem.

I'm also on the "you need a larger stacked plate style cooler" bandwagon.

It sounds like you're creating a very complicated fix to a very simple problem, and creating a lot more space for things to go wrong in the worst possible conditions.

what size and type of cooler? is there a chance that it is partially obstructed? and how old is your trans fluid?

im with most on here. just get another/better cooler and be done. and like XJLI said, if you have not re-geared, you should. your tranny will love you.

XJLI said:

how much overheating? going uphill on interstate 8 in california on a 100+ degree day my XJ was loaded to the brim, i kept a steady 35-40mph the whole climb up the mountains and was holding a bit above 220. i had 33s and 4.56 gears, all good condition cooling components and a small extra tranny cooler. i wouldnt call that overheating.

are you geared? if not, thats your problem.

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yeah that grade will bring out any cooling problems. then with 33's and stock gears. ew for me. 2nd gear 3500-4k RPM.

the radiator cooler is already in use as a water heater for my on-board hot water shower system,
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God I love it. How hot is the water?
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Were is the cooler mounted? Best if in front of the rad/clutch fan. It runs all the time.
I have seen them mounted off to the side with no air flow and no fan of it's own. No good. Clean it out too.
Check lines and hoses to cooler for kinks, pinch points etc.
Check for SOME fluid flow to cooler. Pull supply line to cooler. Place in bucket. Have buddy start engine and sandby to kill engine FAST. SOME flow should come out. HOw much can very a lot. But you should get some.
All is well. Replace cooler with biger unit.

Change you trany fluid. OVER 200 deg and your trany fluid life is cut in half. Evey 20 deg over that and cut that in half. So if it is over heating change it now.

Also make sure you feed *IN* to the *bottom* of the cooler, and back out the top, so your fluid doesnt run through the cooler at gravity speed and back to the pan without having time to cool.

cal said:

I'm also on the "you need a larger stacked plate style cooler" bandwagon.

It sounds like you're creating a very complicated fix to a very simple problem, and creating a lot more space for things to go wrong in the worst possible conditions.

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Agreed.

I wouldn't run tranny fluid through the heater core, it's under enough pressure that I would worry about it bursting, and that ending up under the dash is a recipe for disaster. You'll have to rip the whole dash apart to set the AC system up to do what you want, too. Way easier to just get a better tranny cooler.

i know that the heater core couldn't stand up to the pressure. also you wouldnt get heat until after driving for a while or letting it run for 30mins. but some radiators do have a power steering cooler and trans cooler. also how hot is it getting. i have a stock 89 xj with a aw4 trany. this last summer i took a trip to Oregon loaded down so much that my rear axial was on the bump stops. the highest temp for my trany i hit was 185

I would like to commend you for "THINKING OUTSIDE OF THE BOX".
That said, there are several good posts with reasons why not to do this.
I personally don't know.
I did much to lower my trans temps.
After all the work I found that the main contributer to my high trans temps was the Mobile 1 full syn ATF. I discovered that the hotter the oil got the more the trans would slip and in turn cause higher temps.

I run my fluid thru a B&M High Tech cooler, then thru the radiator. The B&M cooler is mounted on the underside of the hood with the fan on top of the hood. At one time I had a leak and bypassed the radiator, the only change I noticed was that the tranny temperature did not stay as steady. The tranny would make large temperature swings. My tranny will still hit 220 for short periods when climbing steep grades with both coolers. My gauge sending unit is on the tranny output side before the cooler, so it is picking up the TC heat. Now considering I had 140,000 miles before I added the cooler and gauge, I feel once we know how hot the tranny is getting we start to panic. If you did not have a gauge you would never worry! I don’t think 220 now and then is an issue! Just think how hot the tranny was getting without the cooler!

All that being said I have watch my water and tranny temp. and have come to the conclusion that the tranny is heating my water, as the tranny will climb then the water fallows. I think the answer is to install a TC lock up switch; this would reduce the heat created by the TC.

I run two coolers one in front of the radiator on the mechanical fan side and one under the radiator with a fan similar to gojeeps install. I do not run through the radiator anymore. I had a in radiator cooler fail and lets just say coolant and tranny fluid do not play well together. My tranny temps hardly ever see 180 in the summer. Once it got to 195 climbing a steep grade. It mostly runs between 150-160 all the time with the fan off.

jeepme said:

I run two coolers one in front of the radiator on the mechanical fan side and one under the radiator with a fan similar to gojeeps install. I do not run through the radiator anymore. I had a in radiator cooler fail and lets just say coolant and tranny fluid do not play well together. My tranny temps hardly ever see 180 in the summer. Once it got to 195 climbing a steep grade. It mostly runs between 150-160 all the time with the fan off.

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Jeepme, where is your sending unit for the tranny mounted?

another thing that will help your trans temps is an external filter assembly because it will
1 allow you to have more fluid in the system
2 take the fluid along yet another path to give it time to cool before going back to the tranny.

i am personally looking at this because I fried my trans fluid last summer at rausch creek. I changed the fluid 2 times and have not had a problem yet but I am going to do this as a prevention measure.

kcjeep6 said:

Jeepme, where is your sending unit for the tranny mounted?

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Fluid pressure test port on the tranny. KCjeep6 I would bet that if you move your tranny cooler off the hood and plumb it after the radiator, you would see lower temps. When you turn that cooler fan on, it is just drawing hot engine bay air into your allready hot cooler. But then you wouldnt have that awsome Flux Capacitor look.