I have a ‘89 2WD with a AW4, 3:55 gears, 2” lift with 30” tires. I installed a transmission cooler and temp gauge for towing. I recently got an overland style camping trailer, it weighs about 2K. The XJ tows it like it’s not even there, but there’s one steep grade near my house and there’s no alternate route. I took the trailer out this weekend and going up that hill, the trans temp hit 217 degrees towing in 3rd at around 35 mph. The hill isn’t too long, probably a few miles, but when the temp gauge started climbing it felt like an eternity! I don’t want to damage the trans and have to replace it. What can I do to keep it a bit cooler? Is ~220 degrees ok for a few minutes? Would dropping to 2nd gear keep it a little cooler? I’m good at most things mechanical but I don’t know much about transmissions and I’m fairly new to towing. I’d appreciate a little help.

 

check your lock up torque convertor is being activated under normal driving conditions, if it is, it will lock up in 3rd as well

if it isnt that generates a lot more heat

220 is ok for a few minutes in my opinion, mine will do that on a long up haul when towing

if the ambient temp is high, they get hotter

 

Thanks. Ambient temp was in the 80s, but it gets well over 100 here. I’ll take a look at the torque converter.

 

I did the fluid check on the torque converter and it seems to be working. Maybe I just have to accept the trans getting a little warm going uphill. It was only above 200 degrees for about ten minutes, so it’s probably ok. I’d just hate to kill the transmission. It’s a good Jeep, I’d like to keep it that way.

 

Drop it to 2nd and let the motor wind out. Its very likely the torque converter is not locking in 3rd at 35 mph with a trailer.

Using the GrimmJeeper Gear Calculator, your engine speed should be 1392 rpm at 35 mph in 3rd gear with the converter locked, 2129 rpm locked up in 2nd, and 3896 in 1st.

I have no problem letting my motor run 3500-4000 rpms for several minutes at a time when climbing big hills. Don't be scared to wind the engine out a bit, it really doesn't mind. You'll do much more harm pushing up the hill with your converter unlocked.

Try throwing the level down into 1-2 and let the Jeep do whatever it wants to do to hold speed. If 4000 rpms is what it wants to do, let it. Check your trans temp after that. I bet it will be much lower.

 

Thanks. I’ll drop it down to 1-2 next time. I don’t mind winding out the engine. I have temp gauges for the engine and trans on the pillar, so I keep a close eye on them when I’m towing. I need to find a better tach though, I hate the one I have.

 

Did you install the aftermarket transmission cooler before or after the factory in-radiator cooler?
Where did you place it?

 

I put the cooler in a long time ago, I don’t remember how I plumbed it. I believe I ran it from the trans to the cooler, then to the radiator, then back to the trans. As far as placement, it’s in front of the a/c condenser, so it’s right behind the grill.

 

You have it backwards then.

 

I was thinking the same thing. I need to replace the A/C condenser, so I’ll take a look at it when I do that. If it’s backward I’ll fix it, it’s just a matter of moving a couple of hoses. I recall thinking that I didn’t want the trans to run too cold, so I’d let it pick up a little heat from the radiator. I’ll have to see if my trans cooler has a bypass in it. It normally runs a lot cooler than the engine, so maybe I did plumb it right. I guess I’ll have to get under the Jeep to figure it out.

 

Being a transmission builder, my thoughts may differ a little from the conventional school of thought. I always by-pass the radiator completely with the ATF and run a separate cooler sized for the job. (Especially on anything that tows). It takes all that localized heat from the ATF out of the radiator. It adds potential BTU capacity for the increased coolant temp from towing. This way, the ATF doesn't have to compete with the engine coolant for available cooling capacity. The factory is all about combining things into a module for ease of installation and cost reduction. Its barely adequate for minimal towing. You can do much better without any real cost increase. 180 to 200 degrees is the ideal towing temp. range. 200 is getting warm. After this simple mod is performed, If it wont stay below that... Put a fan on it, or go bigger on the cooler.

If you are concerned about the ATF not being up to temp due to cold ambient temps or not warmed up yet, they make an in-line thermostatically controlled valve to handle that. it wont flow to the cooler until its up to temp in the pan.

Personally, I put a check valve inline to keep the cooler from draining back into the pan. This just adds capacity of fluid since it stays in the cooler when you shut the engine off. You can put more fluid into the pan at the full mark. On my Duramax tow truck I installed a simple one wire Autometer (Gauge Company) 200 degree inline sensor on the outlet (cold) side of the cooler. It turns on a basic warning light that grabs my attention. These are available from Autometer along with an inline fitting to install it.

Its good you are paying close attention to the temps, that's the number one killer of automatic transmissions.

 

The factory puts the transmission cooler in the radiator because liquid is far more effective at transferring heat than air. Often what happens on an XJ if you bypass the cooler in the radiator and put a large liquid to air cooler in front of the radiator is it actually causes it to run hotter due to all the hot fluid being in front of the radiator. The best way to do it is keep the cooler in the radiator so it takes the majority of the heat out of the fluid, then plumb the aftermarket cooler in after that, the factory has it set up that way if you get one that has the auxiliary cooler.

 

Yes, location of the cooler is important. Blocking the radiator would obviously be counter productive. But, the fact that removing the hot ATF from the radiator tank dropping the coolant temps is 100 accurate. Mine go under the body with a fan and a thermostatic switch.

 

Well I took the trailer out again this weekend and came home last night. When I got to that uphill portion, I dropped it into 1-2 and made it up the hill with no issues. Trans temp got to 177 and engine temp got to 214. Thanks everyone for the replies. I’m surprised how much torque the XJ has - it flew right up that hill in 2nd gear. For my light trailer, it’s a great tow vehicle. I don’t think I’d ever push it to the 5K tow rating, but it handles 2K with ease.