tranny overcooling

hey all

i installed a B&M tranny cooler and temp guage just like the one on the jeepin.com writeup, except i did a few things differently.

i had broken my OEM tranny cooler hard lines while wheelin and had to replace all the old lines with new rubber tranny cooler hose, this is why i did the mod to begin with.

also, per B&M instructions for the temp guage, i installed the sending unit on the cold side of the tranny cooler (they said it shows the efficiency of the cooler)

i bypassed the stock cooler altogether.

while driving, the tranny temp rarely gets above 110*-120*
while wheelin, the tranny temp stays about 160* varies a little.
keep in mind this is the temp coming out of the cooler, and the thermostat for the engine coolant is a 160* unit. the tranny temp on the guage is always 50* cooler than the engine coolant temp. (ex coolant 160* tranny 110*, coolant 210* tranny 160*)

even using a 185* thermostat that gives me a tranny temp of 135*

is this too cool for an aw4? i am thinking about switching the lines to see what the temp is coming out of the tranny, as this would be closer to operating temp

i have heard auto trannies should operate about 150* and max at like 300*

thoughts?

-Tim

Consider inaccuracy of the sending unit and double check it. My B&M is about 50 degrees off... likely because I overtightened it...

kubtastic said:

Consider inaccuracy of the sending unit and double check it. My B&M is about 50 degrees off.

Overtightened?

Click to expand...

overtightened?

-Tim

I think overtightening the sensor during installation can ruin it.

kubtastic said:

I think overtightening the sensor during installation can ruin it.

Click to expand...

i dont think i overtightened it. however i did use teflon tape on the threads, would that make a difference?

also, i had to run a dedicated ground wire to the sending unit because it is designed to ground itself thru the metal tranny lines, but i used rubber lines. a quick call to B&M tech support cleared that up

-Tim

teflon... hmmm maybe I should check that out. I got a bit on there too.

Best to just do a sanity check here and just grab that line with your hand and see for yourself if it's really only 110 degrees in there...

Because it gets fairly cold here in VA in the winter, I leave the stock radiator cooler in the loop to put a little heat back into the oil. I'm running the largest Hayden cooler made, 30,000 GVW, and it some times over-cools. What I did was go from tranny output line to cooler back through the radiator through the sender back to the tranny. My tranny runs 160* summer or winter. I tow with this XJ every day. I also have a B&M temp guage, here are some pics of the guage sender and of one of the trailers that I tow with my rigs. I have 2 XJ's with the exact same set-up.

I would switch lines, putting the line on the return doesn't give the operating temp of the tranny, just the temp of the fluid after passing through the cooler. You are likely not overcooling as much as your sensor location is leading you to believe.

If you are working your tranny hard, you already know that the oil comming out of it is hot, You really can't prevent that from happening, friction equals heat. What you want to know is that the oil is being cooled properly and will in turn cool the tranny properly, and the cycle repeats itself.

I'm sticking with this theory and it has worked well for me, the XJ shown has over 80k(120k total miles) in towing miles alone, trailers weighing 3k or more.

I don't have one in my my XJ but I do have one in my Barracuda. I agree the hot line coming out of the trans is where you need your sender, otherwise you will never know when your getting it to hot as your just seeing what the fluid temp is going back in.

hey all
thanks for the responses.

i decided to switch the temp sender over to the "hot" line coming out of the tranny, but to make it simple to swap back, i just added hose barbs and put a double sided barb on the other line to close it back. i also rechecked all the wires to make sure they were connected right.

the temp still reads low (110* when cruising) after driving to Douglasville (45 mins) i grabbed the metal part of the tranny line coming directly out of the transmission pan, and it didnt burn me and it was about as hot as water gets from the tap at home.

so i have concluded that the tranny isnt getting much hotter than 110*, i dont know if i have a larger cooler than i need (19,000 GVW) or what.

-Tim

i was hopin jeepin jason would chime in because he has the exact same setup as i do.

-Tim