My brother's van has a problem with transmission fluid leaking out of the dipstick tube hole. It has had this problem through three transmission, two dipstick tubes, new o-rings around the tube, and RTV sealant slathered around the union between the case and the tube.

The transmission only leaks when it is shut off and sits. I am beginning to think that the leaking is caused by fluid draining back into the pan from the massive transmission cooler mounted in front of the radiator (it is the big one in front, not the smaller oil cooler in back):



Is it possible that the volume of fluid contained in this transmission cooler drains back into the transmission pan on shutoff and overfills the pan, causing it to leak out the dipstick tube hole? I am at my wits end trying to solve this leak.

Thanks.

Interesting that it still leaks despite new tube O-ring. Are you sure the tube is in good shape (still round at the bottom, not dented or cracked), and that the correct O-ring is being used? And are you absolutely certain this is where the leak comes from?

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

The new o-ring was tried on the previous tube. I will be pulling this second tube and installing a new o-ring and double checking for damage. This tube and transmission are a matched pair that were pulled from the same junkyard van. The transmission looked clean with no leaks at the junkyard, but leaked when installed in my brother's van. I am about 95% certain that the leak is coming from the dipstick hole. Otherwise, the leak would have to be from the front passenger side edge of the pan and somehow flowing up to the tube. That would be possible if it leaks while driving, but it is more likely it is the tube/case union.

The next time the van is down in my garage I will be inspecting all transmission lines, gaskets, and fittings for leakage, tightness, and warping/deformation. I am going to replace the pan with a different to be absolutely sure it isn't a leaking pan and I will be replacing the O-ring with a new viton o-ring.

But is it possible for the transmission cooler to backfill the pan and cause an overflow? I'm getting to the point of wrapping the tube in teflon tape sealed by RTV goo and then jamming it down into the case....

Yes, the fluid level in the trans will rise after shutdown as the torque converter (and probably the trans cooler) drains down. There are several potential leak points that are normally above the fluid level, which can get inundated with fluid after drainback. Dipstick tube, shift/kickdown shaft seal, pan gasket, neutral safety switch, speedometer pinion/speedo cable, etc.

_________________
一期一会
Too many people who were born on third base actually believe they've hit a triple.

My '64 leaked there for a long time. It finally stopped with careful cleaning of tube and the hole in the case and a new O-ring from Pat Blais.

_________________
"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

OK, thanks. I wil get in there and clean and inspect everything closely.

Couple of things here Reed.Does the van have that real long tube that sticks clean out to under the hood? If so maybe it's getting a small tweak/bind when bolted up leaving a less than even fit around tube to tranny.I second the clean/oil free fit and then maybe kinda force it to seat evenly while your bro checks where the hold 'em up bracket is in relation to it's mounting hole.
If it was me I'd ditch that massive trans cooler,a much smaller one should be just fine if you fellers is towing with it alot and might not be needed at all.I remember reading years ago that 'over cooling' on a MoPar trans was NOT a good thing,almost akin to running an engine at low temps.

_________________
83 B-150 slant 6,4 speed. 79 B-300 360 pathfinder 4x4. 74 W-300 318 4x4 git-r-done 80 B-100 sl6,4speed

I agree with everything you say. It does have the looooooong tube that runs up to the hood, so I will be sure to make sure it is fitting down into the case correctly. The transmission and tube were a matched pair from the same van in the junkyard, but I know the transmission was removed and rebuilt at some point, so maybe the mounting tab got bent.

My brother doesn't tow anything right now, but he did install a class III hitch and might use the van to tour with his band and haul five adults plus a trailer of band gear. That being said, I think the tranny cooler he has now is very oversized, and I might just get rid of it or install a smaller one. I have also heard that overcooling the transmission is bad. Maybe that explains why this van has managed to eat two 727s.

Does it still have the cooler in the bottom tank of the radiator?

If it does, why not just bypass the big cooler, and see if the problem goes away?

Yes, we are actually running the factory radiator mounted cooler and the big aftermarket cooler in series, so a bypass of the big cooler shouldn't be a problem. Good idea!