poni

Hey guys, newbie poster here. Please excuse the long post, I’ll give as much info as I can…

I’m trying to diagnose a phantom intermittent leak from the trans. It’s happened twice, under somewhat different circumstances. I’m running a 99 XJ, 4.0, AW4, 4x4. After the first event I installed a trans temp gauge to help troubleshoot.

Conditions when it happened:
first time, hot day in bad stop/go traffic (85deg, 30-40 mins traffic). I noticed faint white smoke as soon as the tc locked up at around 70kmh. When I parked, atf was leaking on the exhaust near the bell housing. Lost about 1/2 litre of atf, but checking the dipstick color was good, fairly bright red, not burned.

2nd time, after a 2 hr highway drive with no problems, about 15 minutes of slower driving on a gravel road (hilly, so lots of up/down shifting/accelerating) it started to smoke again. Trans temps on the highway stayed pretty even around 140, once I got on the gravel and speed started to vary, temps went up to 190ish.

strange thing to me is it will only leak after the tc locks up around 70kmh when the temp is over 185. Any temp below that is no problem.

I’ve checked trans vent- clear. I’ve cleaned everything and monitored for leaks, it’s dry until I repeat those conditions then it’s wet from the bell house back along the bottom. Engine temps are normal, ~190 confirmed with IR gun.

any suggestions greatly appreciated!!!

cruiser54

When is the last time you did a drain and fill on the trans, and which fluid did you use?

You're checking the level according to the instructions on the dipstick?

poni

Ive only had the jeep for about 7 months (5000km driven), I haven’t done a drain/fill. Since I bought it the fluid looked quite new, I’m not sure what fluid the po used but he was diligent with fluids at his local mechanic. Could the wrong atf cause these symptoms? I topped it up with merc/dex lll.

checked atf as per fsm, engine hot, in park, cycled through gears. Right in the middle of the “safe” range.

as a side point, when I tapped into the cooler line to put the temp sender not much atf dripped out, not sure if that’s normal. Also, the fluid in the line was noticeably darker than on the stick. Thanks

cruiser54

I would do a drain and fill with Dex/Merc. Don't need to pull the pan.

Inspect the metal tubes from trans to radiator. Make sure they're not crimped/smashed.

awg

Your trans temps dont seem excessive, but your sensor is in a cooler spot than mine

If it gets too hot, it may come out the filler tube..is that the case ?

What is the ambient air temp ?

I have a gauge in my '96 oil pump port and it has been over 212F, but typically runs about 185F in 70-80F weather

cruiser54

Good^^ to know those readings based on real world experience.
Indeed the additive packages in trans fluid can wear out or be the wrong ones, causing fluid to come out the tube.

poni

ok thanks, I’ll try that and report back what I find. I’ve read I should repeat the drain/fill process 3 times with brief drives between to be sure to change out the majority of the old. Would you recommend that, or just once?
From visual inspection the lines look ok, no pinches or outside damage, however they look original (240k kms)

filler tube at the top is dry, definitely leaking from lower, either bell house area or maybe o ring on the filler joint.

ambient temps around 25-30C. (Around 80f I think lol)
I’ve compared various points on the trans with IR gun, pan, body, in/out lines at trans/cooler. They’re all within about 25 degrees of each other so my location might not be exact temp of the internals, but it lets me see any spikes in temp which I haven’t seen. Usually in the 150 area, seldom over 175.

cruiser54

Clean it off and closely inspect that dipstick/o-ring connection.
Could be if the fluid didn't foam, it would never reach the o-ring area?
Because we don't know which fluid has been used, I'd lean toward at least 2 drain and refills.

poni

sounds good, easy step to eliminate a possibility. I’ll get to that this weekend and post back. Thanks cruiser!

cruiser54

Can't hurt and could help. Have a good weekend.

Randy Bobani

Fluid is much more likely to puke out of the breather than the dipstick tube.. The breather is on top of the transmission, just behind the bellhousing flange. Fluid will puke out of the breather when hot, if the trans is over filled. Your trans was over filled. Dump some fluid, add fluid to proper level by reading dipstick while engine is running, trans in Park (or Neutral, doesn't matter).

poni

I checked the vent, it’s dry and clear. No atf has leaked higher than the o ring on the dipstick tube for sure, completely dry from that point up. I keep a close eye on the levels, it was right in the middle of the safe range before the first occurrence. Only added about 250ml to get the level back up to the middle of the safe range after the leak.

cruiser54

Isn't the o-ring for the dipstick tube lower than the vent anyway?

dzywicki

IF it's coming from the bellhousing, it is most likely the front seal on the transmission. When that seal starts to go, it will leak as the fluid warms up and expands. IT will leak pst that front seal and drip out the bellhousing onto the exhaust and make white smoke. Top up the fluid, clean everything, go for a drive. Once you park, leave it running and look at the bellhousing drain area.

poni

yep 😜

I was suspecting front seal. I cleaned it up and did as suggested, but couldn’t reproduce the leak. It was probably 2 months between the 2 leak events with zero leaks, even after long highway/city drives. I figured if it was a bad front seal it would leak pretty consistently after reaching operating temps. I can drive it all day long, highway speeds, side streets, no problem. Would a bad front seal be so intermittent like that?
Only seems to happen when it’s really hot ambient and I get caught in bad traffic, or the second time the trans was working pretty hard on the gravel road with hills and lots of acceleration/slowing down.

since it seems temp related, even tho it happened with trans reading around 185f, I’m thinking maybe restricted flow thru cooler? No pinched lines or anything, but maybe buildup inside? I could do the flow test from fsm but I’ll start with cruiser’s suggestion and go from there. I’m a firm believer in starting with the simple solutions, po using wrong fluid is pretty simple 😆