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Old 06-26-2009, 05:45 AM
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Default Transmission leaks/overflows when hot

My 99 Cherokee with 4.0 and AW4 has poured transmission fluid all over the place twice. Both times has been when it is very hot outside. The only reason I noticed it was because of huge clouds of smoke where it is burning on the exhaust. It is difficult to tell just where it is coming from because it's flying everywhere. Once I stop, the leak stops almost immediately. Because of the large amount of fluid coming out and the fact it stops when cool and doesn't leak ANY most of the time, I don't thing it a normal leak but more like it is overflowing somewhere. I know VERY little about auto transmissions. I do understand it has a vent on the top, but I can't seem to get to it. Can anybody help? There was a similar problem mentioned in a post several years ago
http://forums.off-road.com/jeep-mid-...ak-coming.html (got a tranny leak, coming from ??),
but not the end result. I don't think it is the main seal or surely it would leak at least some all the time.
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Old 07-05-2009, 12:58 PM
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You've got me swinging, but it is a curious event that I'd like to see figured out. That is, it's worth hanging with just for the experience.

I don't know if they snorkle the vent on the AT in the Chero. For that matter, I don't know if they snorkle the AT in a Wrangler. The do everything else.

I'd really take note of exactly when the condition starts. You're not saying if it's when you're climbing a grade ..idling in traffic ..at highway speeds .. Try and be a bit more critical of the surrounding circumstances on the next event. Rpeat the conditions that create the event while altering one or two elements.

We'll then progress to "I can avoid it if I ......." or "it gets worse if I ....".

If it's not boiling out the dipstick tube, then the vent is the most likely spot. This would be a hard thing to happen without an accompanying coolant issue for the engine. Your in rad cooler may be ineffective/clogged/dysfunctional.

Whatever the cause, boiled aerated fluid is no good for your trans.

As a quick "see if this helps" maintenance item, take the trans cooler lines off at the transmission. They should be easy to detach. If it's like my son's 00 AW4, there are two "pinch tabs" that are plastic wedges that hold the hard lines in place. You manipulate them (push, pull, pinch) and the line just pulls out. It goes back in easy enough too. Take both of them out of the trans.

Then take either carb cleaner or brake clean and stick the swizzle stick in the tube and seal around it good with a rag. Run the whole can through if you can manage not to leak too much out of your end. Run two cans if you have to, but assure that you're producing flow out of the other hose.

I'd prefer some lower pressure air to chase the stuff, but if you don't have that, it's not all that big an issue. Most of the components in the brake clean will volatilize on their own. Carb cleaner will have some residuals (probably) but after you lock this down, I'd recommend a ATF swap in the same manner. There you merely detach the rear most cooler line and place it in a drain pan ..and pour the new fluid through the dispstick. That purges all the fluid. It will take about 10-12 quarts to get most of it out.
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Last edited by GeeAea; 07-05-2009 at 01:07 PM.
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Old 07-05-2009, 01:20 PM
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Default More Details

Thanks for replying,

I can give a few more details. First, it has only happened twice, about 8 days apart. Both times were as I was leaving a 5-10 minute wait at the Burger King drive thru. Perhaps I should just avoid BK? Anyway, the first time I had driven about 15 miles mostly city driving with a 10 minute or so stop in the middle. After mostly idling at the drive through for 5-10 mins, then pulling out into traffic, the smoke started. I stopped again about 5 miles later for ten - fifteen minutes then drove 5 miles home. Still the leak/smoke. At first I thought it was oil. I cleaned everything underneath, changed the oil. Nothing for 8 more days. This time, after 35 miles freeway driving I went about 2 miles city, then 5 miles or so of near constant 60 mph with a couple red lights, then 1-2 miles city to the BK. Again, pulled out from the drive through and shortly the smoke started. Drove it home, leaking and smoking. This time, I checked it better and found it was trans fluid. Again, there have been no leaks since. Not a drop. From where it was going it seems to be coming from the top of the tranny, but it goes everywhere so is hard to tell. I suspect the vent. I believe it is on top near the front, but can't seem to get to it. I can't even tell if there is a hose connected to it.

The temp gauge did go up about 5 degrees. It usually stays locked on 210, but occassionally will get to 215 or so in hot weather and city driving. It went to about 215 both times. I don't know if before or after. I THINK I had the AC running both times. I know I did the second time. The fluid doesn't appear to be burnt. It looks and smells normal. I have not run the AC since, thinking this might contribute to the problem which I'm nearly sure is heat related. I considered changing the filter but am waiting on advice from more knowlegeable people since I have heard too many horror stories of new fluid causing new problems. Thought about changing filter, filtering the old fluid and putting it back in.

I'm a decent shade tree mechanic that's had a wrench in my hand for 30+ years, but I've never even heard of this before. I know little about Auto Transmissions so any help / advice will be greatly appreciated. I don't have the money right now to take it to a shop and suspect most of them would scratch their heads also.

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Old 07-05-2009, 02:01 PM
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Thanks for the additional good info. Don't worry about a full fluid swap. 99.99% of those rumors are from people who never change their fluid until something goes wrong ..then they change the fluid ..and the problem lunches the trans ..just like it would anyway.

Yes, this tends to look more and more like a cooling issue. Adding an auxiliary cooler isn't that easy in this setup ..at least if you want it up front. There appears to be plenty of room under neith, but I'd still do the in rad cooler cleaning as I described. I'd recommend putting a Magnefine inline filter (NAPA and others), but since the Cherokee uses either hard lines or crimp connections, it's not a seamless procedure. Doable, surely, but more involved.

Pan filters are sieves. Anything on the suction side is just to catch chunks.

The AW4 is a great trans. Failures are rare even if hammered on a bit.

While fluid can get burnt by over heating, it's usually a slippage/friction deal. You're burning up many things that the fluid carries away. Once overheated, ATF is a poor lubricant. It's more of a coolant with some lubrication properties.
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Old 07-05-2009, 02:36 PM
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Default Sounds like a plan!

Thanks again!

I will try cleaning the cooler in the next few days, first chance I get. I think you are right, it is a cooling issue. I have had this jeep 4 1/2 years and about 70,000 miles and never had such a problem. So I don't think I need to add an additional cooler. I'm pretty easy on it. Mostly it hauls me and my kids around town and on our "big adventures" which sometimes end up on some trails. I don't take it out mud-bogging or mountain climbing. I will flush the cooler like you said, drive it a little while, then change the fluid. Probably go ahead and change the filter while I'm at it. At least see what's in there.

One last question if you don't mind. When purging the fluid, is that with engine running or not running?

I really appreciate your help. I will try this and get back with the results.

Thanks
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Old 07-05-2009, 05:06 PM
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Yes. It's easier as a two person deal. You just unhook the rear line and hang it over a pan..run the engine in PARK (if specified on the stick - some require NEUTRAL due to the cooler in some models being valved out in PARK - though I've never encountered it in a jeep) ...when the flow stops (you get bubbles) shut the engine down. NOW WOULD BE THE BEST TIME TO DROP THE PAN - it's almost empty . Repeat until you've only got 3 quarts left of your 12 quart supply. Hook the line back up ..add 1.5 quarts and check level (run it through the gears). Add until you JUST see it on the stick ...run it for a few miles to assure it's heated. Recheck and top off to HOT spec.

The fluid added via the dipstick tube, being cold, will confound good readings (usually) as it will drip down on the stick where the tube and stick meet inside it. Once hot, it doesn't cling ..but then again, it never creeps up the tube.

Your total fill is allegedly 8.3 quarts. To purge most of it you need about 50% more due to mixing in the converter.

Good luck!
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Last edited by GeeAea; 07-05-2009 at 05:15 PM.
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Old 07-13-2009, 04:36 PM
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Default 91 jeep cherokee tranny fluid flows out of breather when hot.

My 91 Cherokee Limited is doing the same exact thing. Looks like it is a cooling issue. I haven't had this Jeep very long, and I just noticed that the auxilliary cooler is out of the loop. I will try hooking it back up and see if that helps. Also having a cooling system in good shape is important, I hear, because if the engine runs hot, the tranny runs hot. (Mine runs at 200 most of the time.) A good tranny guy just told me the higher temperature makes the fluid foam and out the breather it comes. Also could be bad gasket in the valve body, but that would pressurize the pan and send fluid out the breather all the time, not just when hot. The pump may be worn out too, as this would decrease circulation and the tranny would overheat easier. First thing to do is check fluid flow. Make sure the fluid has a healthy flow and the lines are not bent or plugged. That is the stage I am at. Good luck.
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Old 08-11-2009, 01:43 PM
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Default 99 Jeep cherokee 4.0 Auto same issue - leaks when hot

My recently acquired 1999 Cherokee 4.0 / auto started this same issue in June, and it leaks - as in little stream of fluid - once it's driven about 5-8 miles city. The leak continues for a 30-secs to a min when turned off, seeming to indicate it's over heating NOT direct over pressure/leak from running(?). I am mechanically inclined, but have not done tranny work. I will post as I get more info - hope others will do the same. The leak appears at the FRONT of the tranny, on the passenger side, mid to low level. When driving, the fluid is pushed back up the where the tranny pan is, and leaks onto the exhaust making smoke. I'm starting with the premise that this is an overheating issue, as the engine "seems" to run hot. I have a 2WD with idiot lights only. - The tranny also does not seem to shift from higher gear to 1st when I stop, especially if I stop quickly, it takes a few secs, then a little "thud" and it's in low. I've heard about a speed sensor to clean out??
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Old 08-11-2009, 04:59 PM
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I'd get a bottle of Auto-Rx (Auto-Rx Engine Cleaner Transmissions Motorcycles Stop Leaky Seals Oil Burning Increase MPG Better Gas Mileage Trouble Shifting ARX) and follow the recommended instructions for automatic transmissions. Then do a cooler line fluid exchange. I recommend this due to your shifting issues. If you want to determine if heat reduction will cure the problem, rigging an auixiliary cooler ..even temporarily under the floor (hassle up front), is cheap. If you've got an IR gun thermometer, you should be able to see the outbound ATF temp through the line.

The Auto-Rx will clean out your in rad cooler of anything that is preventing good heat exchange. Even the normally "warm" running Cherokee has more than enough capacity to cool your trans. If your coolant is in control, so should your trans temp. Liquid:liquid heat exchangers are much more efficient than air:liquid radiators. The density of the coolant trumps size by a large margin. (for others that may be reading) Think of how you can be comfortable in 70F air ..think of how you'll eventually shiver in 70F water.
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Last edited by GeeAea; 08-11-2009 at 05:03 PM.
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Old 08-16-2009, 12:33 PM
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There is no problem with the standard fluid and filter change. It is this big push to do "full trans system flush" that causes issues, also swapping out the fluid 2 or three times in a very very short period of time with the thoughts of "getting out every drop of old fluid including that which is in the converter". The problem arises with a vehicle that hasn't had proper fluid changes throughout it's life. They start to build up deposits in the passages and valving and then you flush out all the old fluid and put in all new fluids and with their brand new detergents it starts loosening up the deposits and causing that crap to start circulating around and that's what will jam up the valving and plug passages. A properly maintained vehicle WILL NOT suffer any detrimental effects from a proper fluid and filter change. And changing fluid in the proper manor should not cause issues either as your only replacing some of the fluid and not giving the trans and "overdose" of detergents.

As to the issue at hand, trans fluid blowing all over, check the vent tube on top of the trans for starters, yes the "snorkel them on the XJ auto trans too. If that's clear, then over heating fluid is a good possibility and you'll need to find out why it's happening. I would be looking at the brakes also, as a dragging brake would cause more heat buildup in the trans, not to mention the damage it can do at the wheel that it is dragging on. Can wipe out bearings and seals in a hurry. It may not be your issue but would be worth checking as it can be a "free" diagnosis you can do yourself.

As for adding anything other than transmission fluid, I personaly do not use or recomend "Magic fix in a bottle". That can be just as bad as a full on trans fluid flush, again knocking sludge and deposits loose and causing trans failure.

Just my opinions on the subject for the moment. Good luck.
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Last edited by krabysniper; 08-16-2009 at 12:35 PM.
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