It seems Jag used different sizes of plugs over the years, this one’s M20 with 1.5 thread pitch. M20 is about 3/4 inch…rather big. Not sure why the original plug is marked 12.
I tried a new plug hoping new threads would be enough, but the pan threads will not hold. I tightened it all I dared, and it leaked a quart in a few days.
So I’m looking at Heli-coils and Time serts.
Wow, the Time Serts are $300, with 4 thread inserts, drill bit and install tools.
Heli-coil kits don’t seem to come with the appropriate drill in the kits.
The Time Serts seem a better fix, with its chamfered fit.
this seems to be not unusual; my own car has received a new oil drain plug as well - way before my time, but the AF size of the plug is breath-taking! Not far from what you would expect on a Cummins Diesel …
I see one possible direct cure to your problem: oil plugs are typically cut conically to provide for a seal. Maybe you used a standard size bolt? A secondary cure sparing you the helicoil fix would be another oil pan; they are available at reasonable prices and can be fitted once you “let down” the front suspension cross member.
I don’t think Jaguar changed the drain plug, Robert - no reason why they should…
I noticed that your pictures do not show the necessary copper washer? On the plug there is unthreaded bit under the hex - and without a washer the sealing would at best be uncertain.
Sealing would be worse if the plug was cross threaded, which sometimes happen - or indeed a plug with the different pitch was fitted. Once in a blue moon a drain plug is lost - and even in a bluer moon a wrong plug is fitted…
The torque is specified to 26 lbsft and should really not be exceeded. The safe way to avoid either is to seat whatever is fitted by finger tightening before tools are applied - it is impossible to cross thread or seat a wrong thread by hand.
You say the ‘it won’t hold’ when torquing which I take to mean that you can torque but that it leaks - implying that the threads are not stripped…?
So…fit the appropriate washer - and if you do have one, not shown, anneal or replace it; and see what happens. You should also check the mating surface on the sump is undamaged. And indeed that the hex, when seated, is parallel to the sump surfaces - any leaning imply cross threading…
After all that, if it still leaking - you/we may consider other options…
Jochen, I hope I never have to lower the suspension as you have, but that’s a great picture. I love the pastel greens Jag used. I had a Willow S1 for 36 years.
So, It seems this pan has been threaded before. Frank, you are right, all the 6 cyl parts cars I have are the same, a smaller size. Also I see the plug that was in there is a self-tapper design. I think it just bores a slightly bigger thread size as it’s driven in. This is the least reliable type of repair.
I’ve ordered a 3/4 16 Heli-Coil kit, and new 3/4 16 drain plug. Hopefully that will fix it. I’ll check the flat mating surface as well - good thought.
Another option is to seal the drain plug and start using a vacuum oil changer. I did that on my XJ6 and it worked fine. I was a bit doubtful about completely draining the oil using the vacuum.
So, before I sealed the drain plug, I did a test and emptied the sump using the vacuum. I then opened the drain plug and there was only a dribble of oil came out for a couple of seconds.
