Found the cutest little cooler

On wifey's 88 limited 4.0 AW4. it sits in front of the A/C condenser, is a double-pass cooler, (makes 1 "U" ) approx 2.5" x 15"

Would this be an OEM aux tranny fluid cooler or oil cooler? it looks fairly tiny for an ATF cooler...maybe convert it into a PS or engine oil cooler if it is for the tranny.

The Jeep has a 2" receiver (maybe OEM) and thus might have come with an aux cooler. We may tow a little with it, and in the plans were a bigger tranny cooler/gage and remote filter mount.

TIA

Woody

Woody,

You are right that is the factory aux transmission cooler. If you actually measure it the finned area id 16 x 3 which gives you 48 sq in of cooler. The U-tube being so long and thin makes it look small but if you look at aftermarket aux coolers you will find this one.

I looked at the B&M site and they sell a cooler rated for 16,000 lbs and it's dimentions are 11"x5-3/4"x3/4" or 63 sq in of surface area. So IF the ralation of cooler size to vehicle weight is a straight line relationship, which it is not, then you'd only need 32 sq inch to cooler your transmission.

Being a Mechanical engineer I know sizing heat exchangers, that fancy name for this cooler, is a black art. Just because you double the size of the heat exchanger does not mean you will get double the heat out of the fluid.

I installed the same cooler on my 88 XJ three years ago when I I was moving and thought I had to move myself. I have full confidence in the sizing. Remember the guys who picked out heat exchanger took in to account how the XJ was rated and where it would operate it. Also they provided you a warranty if you had it installed and towed up to 5000 lbs.

I would leave it alone and follow the owner's manual service interval of 15,000 mile for ATF changes if you plan to tow and DO NOT use Mobil 1 ATF in the AW4 transmission. I lost 3-4 mpg using it and ended up having the transmission flushed at the dealer to get back good old Dextron.

If you are concerned about AFT temperature I'd spend my money on buying an AFT temp gauge and install it in the oil cooler line, the Mopar perforance web site had a very nice block you placed in the hard trans line. You cut the line and remove approx 1 inch of tube, then you install this block with ferrel type fittlings if I recall then you screw in your temp sensor to the block, very sweet. This way you can monitor ATF temperature and know if you have too hot or too cool AFT.

Here the block I talked about: http://www.mopar.com/m_perf_parts_product_part.jsp?categoryID=10013&itemID=342

In case the page does not work here the P/Ns
P4876057 5/16" O.D. tubing
P4876058 3/8" O.D. tubing

Then buy the gauge and gauge pod of your choice and install. Nothing like having another gauge!!!

HTH

Martin

Thanks for the quick reply and tech/part# info Martin! Is this aux cooler independant of a radiator cooler or is it in conjunction with?

I didn't figure that it would be a linear upgrade to increase the size of the cooler (double would increase the volume a bit though) And I do think a remote filter with 5k swap & top-off interval would be better than just doing lowly prole pan-drains@15k

I suppose the best bet would be to do this mod right after a professional flush/ATF exchange...supposedly this is a freshly rebuilt tranny (less than 5k on it and it does fine) so that maybe a worthwhile expense to have the break-in goo get gone.

Thanks for the PN for temp gage plumbing...and advice on M-1 Synth ATF...LOL it works good in a 231 gearcase though, never tried it in AW4.

Thanks!

(you wouldn't be one of those Air Cav looney pilots would you?) Nice avitar in any case,

Woody,

The plumbing for the AW4 runs from the Trans - radiator cold tank cooler - aux cooler - back to the trans. So the Aux cooler you talk about is in series with the cooler in the tank.

To remove the aux cooler you have to remove the front bumper, all in all I am impressed with the item. Also if you pull off the grill and look on the bottom side you should see a label saying Modine and giving the part number. My thoughts are AMC told Modine we need a heat exchanger for the XJ, design us something that will work. Also there are not plastic ties holding the cooler to the AC condensor so no chance of making a hole and losing the 32 oz of R-12.

You have me thinking once I get my XJ fixed I may install a Transmission oil temp gauge. On April 14 I had a 19 year old run a red light and hitting me while I was waiting for the same rad light. She hid me on the driver's side passenger door and turned the XJ 90 degrees. That was after she clipped the bumper of an 18 wheeler and bent it 30 degrees forward.

If I did this project I am not sure which oil line to install the sensor. I think the returning line then you would know if your cooling system is working. I may have to ask a dealer mechanic where the sensor is located on the newer trucks, you know see what the convention is

As I was talking before heat exhangers are a black art. Even if you go larger you may not get much more heat out of the fluid and you know having fluid too cool is also bad. Heat is rejected by the heat exhanger in this case by convection and radiation. Both are dependent on ambient temperature and no matter how hard we try the fluid will only cool so much.

When I took heat transfer we did fin problems and modeled a fin and found out at 1/2 inch it rejected 99.4% of the heat, at 1 inch long it rejected 99.7% of the heat. So that extra half inch of material cost you weight and gave you essentially no increase in performance. You can see this at work next time you look at an air cooled motorcycle engine.

I agree Mobil 1 ATF works great in my NP 231 and I have 75W-90 Mobil 1 in my differentials but only use dextron with the cert number on the bottle in the AW-4.

I would check the rubber hoses on the ATF cooler lines. Three years ago my hot line was seeping and I decided to change both while I was that far into it. Check your hot line to confirm that is not seeping.

The Avitar is one of the available. I am not an Army Aviator but I do have a set of Army "Master Aviator" wings given to me by a First Sergent and a CW4 for when I was doing flight test. I am an Army Civilian - NOT a Contractor - and am the engineer for one of the Army's Helicopters. Most of my aircraft are used in Cavilary units so though the Stetson was a good Avitar. Not to rub it in but I do have 45 hours as a crew member in Helicopters and even have 4 hours of actual flying an UH-1 Iroquios (Huey).

Martin

It might be more meaningful to measure the temp in the pan which is what RV and trailer towing folks tend to do. B&M makes a aftermarket drain plug kit and it so happens that their tranny temp sensor is treaded the same as the plug.

LOL I thought about a bed mounted radiator for my fantasy MJ... run hard coolant pipes back to the bed with 'flutes' (not High $ fluted thick tubes, but steel tube with flat stock 0.5-0.75h x0.125 th fins) welded or brazed longditudinal like where clearance allowed.

Appreciate the insight into fin area vs weight of the created apparatus vs benefit realized. I'm a civil engineering tech/shade-tree jeeper and always enjoy tidbits of brainfood from real Mech Eng. types...especially ones with aviation focus.

Thanks

put one temp sensor on the out line, one temp sensor on the in line and one temp sensor on the pan.

then you have all your bases covered

(i like gauges)

Talking about the flush, you already have a drain plug. Just change the filter and fluid, drive a while, dump the pan with the plug and you've gotten (1-.5)^2 of the fluid or 75%. Do it three times and you get 87.5% of the fluid. Or better yet change the filter, then every 5 or 6K miles pull the drain plug. On the third time do the full filter change. This way, no one is screwing with your cooling lines or pumping the fluid backwards and backwashing metal particles into the tranny and you're not paying someone $100 for a service you are providing to yourself free. I got the OEM cooler after tallking to Martin and it is working great. I don't have a tranny temp gauge but my coolant temp stays below 200F (measured at the T-stat cover)no matter how hot it gets.

I rigged a tranny temp gauge not too long ago...right after i installed the new tranny oil cooler.

I installed the sensor on the "in" or "send" line to the cooler...that way i could see exactly how hot the oil was, and hopefully the cooler would bring that temp down some.

(i also like gauges

you could use just one gauge, and have multiple sending units, 1 on the send and 1 on the return to the cooler.....and then just rig a 2 position switch to select which sending unit u want to monitor.
depends how fancy u want to get


CaptTrev