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Here's a tale - my 1996 4.0 Celebration has recently had a gearbox fluid flush and refill using a Wynns system that sucks it all out and then refills with fresh - we had to get an adaptor made to get the connections right but all went OK - or so it seemed! Wind forward three weeks and it is time to take the car for a decent run across Devon to Dunkeswell to pick up essential cider making equipment - so a reasonably fast run on a coolish day on A30/M5/A30 - no problem and good for the car after weeks sitting around in various workshops and the barn....
I get to Exeter and off the A38/M5 to rejoin A30 towards Honiton (approx 35 miles) - stopped at traffic lights - window down smoke belching out around me - smells 'orrible - no warning signs anywhere, car running well, gears working as they should - pull over couple of miles further up the A30 get down underneath to find ATF dripping away onto and around the gearbox mounting spring assembly and onto exhaust! Engine still running check ATF level and it is somewhat over the "HOT" mark on the dipstick, so plenty of fluid. Drive slowly to Dunkeswell and check again - still plenty of fluid in gearbox. Let the beast cool down. Drive back towards home steady pace no more smoke, no more drips, gearbox level good and steady! Park up in the barn and this morning no drips or sign of leaks anywhere........whats happening? Anyone any ideas? Filled with too much fluid on flushing? Is there an overflow on the gearbox to exhaust excess fluid? Grateful for any input.......Cheers - Steve

Hi Steve - I had the same thing once when I overfilled the gearbox on my Celebration. If the level is above the HOT mark then maybe that's the answer.
Try sucking some out of the dipstick tube?

You probably just overfilled it, and it may be coming out the gearbox breather - if it has one. I had to chuckle as it reminded me of a similar smoke problem with an old Rover 3500 Vanden Plas EFi. This had a magnificent 'James Bond' smokescreen whenever it had a period of enthusiastic driving, but was OK in normal use. I don't know what gearbox the XJS has; when the underside is plastered with ATF it's difficuIt to pinpoint the source and I had all sorts of things changed to stop it including driveshaft oil seal (twice), dipstick tube seal, and the gearbox breather - maybe your source of oil spill - but on the Rover GM180 gearbox this eventually turned out to be caused by a problem with the seal round the kick down cable mechanism, dripping ATF on the hot exhaust.

Thanks David, Brian - good to have voices of reason and experience out there. The car is going in for service/MoT next few weeks will get a once over then but I feel we have the explanation - Cheers - Steve

Remember you need to get the fluid hot in the gearbox and to cycle all gears parked on a flat surface and then take the reading about five times to be sure. Easy to overfill otherwise and it will escape and smoke.

Nick