AW4 leaking, but only when hot.

I need help with my tranny. It is blowing trans fluid out from the bell housing area but only when towing a trailer, and no it is not overfilled in fact I have drained it down to just below the add line and it still does it. It has a tranny cooler on it but no temp guage. I have pulled over after it starts puking fluid (this is real obvious because of the smoke screen behind me) and checked the temp of the pan with an IR thermometer it reads about 220-230. I'm not sure what constitutes too hot though. As long as I'm not pulling a trailer it never leaks so I assume this is related to the head buildup. What gives? is 230 too hot or do I have a bad front seal? I don't see why a seal would only leak when hot :dunno: does the fluid thin that much as it gets hot? Oh yeah it's a '90 4.0L NP231 if that matters. Also the cooler measures 5x18 and the factory cooler in the radiator is plumbed in as well.

Thanks for any help
Luther

First off, yeah htinning fluid does make that much of a difference. i had a leaky rear main on my old 4.0 that only leaked when hot (& bothered, like when i tramped it passing uphill). other than that, it was fine to putter around all day long.


Now, are you 100% sure this is trans fluid? I only ask because in my real world experience (and from reading online), the AW4 seems to be super-stout...though that rear main is cruddy.

If it is the AW4, check the trans cooler lines - make sure that sucker is actually pumping the fluid through properly. I'd recommend getting a gauge into that loop, too. IIRC, 220 is a tad on the hot side.

Also, how much weight are you towing - is is in excess of the rated limits for your rig? If it is, that could be part of the problem - making things work much harder than designed.

After all that, you may want to have the tranny professionally flushed/cleaned to ensure all the passages are clear and fluid is circulating properly.

Anyone think maybe the torque converter might be wonky? I have never seen what happens when they start to fail...or if they even can fail, but since he's checking things...

HTH - when you get things sorted, post up the problem and the fix for others to reference please.

I had the exact same issue- bellowed smoke and PUKED fluid. The pump seal for the t/c snout was bad. I found a burr on the snout and am certain it was done intentionally. It was rebuilt not too long before I bought it.

Anyway, I replaced the seal and installed a sleeve over the snout of the t/c and no more leaks. I also installed a tranny cooler, as it still seemed unhappy after getting to full temp.

I have other issues now, but for the leak, that took care of it.

Thanks for the responses.

To answer a couple of questions: Yes I'm sure it is tranny fluid, when it does puke it dumps enough for me to see red fluid dripping when I crawl under it and if it is bad enough, even puddles of it on the pavement. The load I'm pulling is not that big, just a 5x10 utility trailer with very little weight on it (usually a go-kart and a truck box mounted on the front).

From the responses so far it looks like I probably have a leaky front seal (at the torque converter) so I guess I will have to drop the tranny down and replace it, I didn't know that sleaves were available for the T/C so I will look into getting one of those as well so that I'm prepared should I need it.

As for the temp: If 230 is on the hot side then maybe I need to look into why it is getting hot as well. I have checked all the tubing and hoses, nothing is kinked, doesn't mean I don't have a blockage though. What size cooler is recommended? From looking on line I think my 5X18 is probably about "medium duty". I have also found some listed as "high efficiency which have flat tubes as opposed to the standard round tubes with fins like I have.

Smokey said:

I had the exact same issue- bellowed smoke and PUKED fluid.

Click to expand...

LOL is that how you got your user name?

you should look for a restriction in the cooler lines or cooler itself,

Another common cause for overheating is the torque converter not locking up. You should also run it in 3rd when towing to allow the t/c to lock at an earlier rpm, and discourage a lot of 3 - 4 shifts

The sleeve, I think, was actually for a harmonic balancer (crank snout), but homie cross-referenced the size and came up with it. Be careful not to press it down too far or the new seal won't touch it. I have about a 1/4" gap from the flange of the sleeve to bottoming out on the converter.

desertjeeper said:

LOL is that how you got your user name?

Click to expand...

Funny, but no. Had a dog named smokey, they started calling me smokey (he was crazy, not unlike myself !!), and I smoke...

speedi-sleeve is what the sleeves are normally called. I think that's the company that makes them.

230* is pretty hot. I think my ZJ got that hot once. I was climbing steeps hills (2nd gear) with 3 people in the Jeep and 80* out.
Normally with highway cruising it will run 160-180* I do have an extra cooling, which I'm sure helps.