My S3 has been parked for the last 6-8 weeks with the cooling system partially disassembled. (I’m working on it as and when I can). Over the last few days, it appears to have begun leaking transmission fluid; bear in mind it hasn’t been started or moved at all since it was parked. Any ideas what would cause this? The only thing I can think of is the overnight temperature has dropped over the past week or two into the low 40s (f). Could that be enough to shrink a seal or something and cause a leak? I’m baffled.
You might look at the ‘vent-tube’ to see if the fluid is coming from that.
I remember having a Borg Warner 65/66 XJ sedan sitting in the corner of the shop for a few weeks and seeing fluid leaking from the gearbox vent. I don’t know why it would overflow (torque converter draining?) but it does happen.
bob
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one thing to check is the transmission shifter seal, it can leak quite a lot (but not usually like that!)
in any case, to trace a fluid leak, I follow a procedure (not much fun)
jack up the car, and fully clean the offending area with degreaser and rags, until it is so clean a white rag can be wiped across it. During this process you may be able to spot the leak
operate the vehicle for a very short time and examine suspect area with bright light.
if you made it clean enough, a new red trail will be there.
the shifter seal fools one into thinking its the pan gasket, but is about 2" above it
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My S3 starts to lose ATF after 3-4 weeks. Drips only. I assume the valve body drains, eventually reaches the shifter seal - I’ve heard that before - or something like it and starts to drain after a while.
If you can it might help to start it up, run through all gears before it gets hot?
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Hopefully that’s all it is. Unfortunately I can’t safely run it until I finish the work i’ve started replacing the water pump, radiator, hoses etc. I plan on spending a few days with it over my extended weekend this week. Hopefully I will get it all back together, but you know how these things go, there’s usually something that crops up and throws a road block! Fingers crossed she’ll be running again on Monday.
Paul,
This type of transmission fluid leak in non-running car is a common problem with the BW66 automatic transmissions in the Series III XJ6s. There must be dozens of posts about it in the archives. I experienced it with my two XJ6s when they sat awaiting maintenance and all three of my Series III XJ6 parts cars also leaked when they sat awaiting dismantling. So all five (100%) of the Series III XJ6s that I have owned leaked like this when they sat for a few weeks or more, although some leaked more than others.
I have read that this fluid leak is due to fluid in the torque converter slowly draining back into the transmission fluid pan over time when the car is not used not used and overfills it the pan. If the gasket between the pan and the transmission is old and cracked then the overfilled fluid drips more quickly than a good new gasket. I have removed and replaced a few of those pan gaskets myself (a rather simple task), found them badly cracked from age, and after I installed new gaskets they reduced the amount of leakage but never completely eliminated it. Especially if the car sat for a month or more.
If it is any consulation, both of our V12 Jaguars with the GM400 transmissions have similar drips even after I changed their pan gaskets (a real PITA job on a V12). I keep a drip pan under each car and find that if the cars are driven at least once every week or two there is little or no fluid in the pans. If any of them sit for more than that I can expect to see fluid in the drip pans.
So my recommendation is to live with the minor leak for now, use a drip pan whenever the car sits for a week or more, and replace the pan gasket when you can to at least slow down the amount of leakage. Then once your current work is complete, try to drive the car at least once a week to minimize transmission fluid leaks.
Paul
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Thanks Paul, (and all others who have responded). I appreciate the information, and feel better about the situation now. It sounds like once i’m able to run the car again (hopefully next week), the leak will stop. There was no leak when I was driving it. I plan on doing a trans fluid and filter change in the near future, so that will take care of the pan gasket.
Once again, thank you all for the info!
Thinking back a about a year and a half I had my S11 in the garage to do some bodywork and after a few weeks it did a fluid drop as described. Cats and marking their teritory 
I dont know on the BW66, although I have one sitting around, but on the BW8/12, the pan gasket is immersed below the line of fluid at rest, by a couple of inches maybe.
whilst driving, enough fluid may be retained within the hydraulic system to drop the level.
after just doing some trans repair work on another vehicle, I again recommend a very thorough clean of the trans area…this allowed me to spot that after fixing worn out old parts, bodgy PO workarounds, there was also a crack in the steel line to the trans cooler
Same for the 65 and 66, level is probably below the shifter, etc. seal as long as the hydraulics are full of oil, but always above the pan seal. I think it is about three inches, but should check my spare dipstick tube to give a real value.