1986 XJS-V12 Engine

My mechanic said that water got into the engine and he can’t figure out how. It did sit outside for a while with a cover. He can’t get it started and I have no idea where to get any help. I live in Georgia and I have even tried to find a used engine. Any suggestions would be great.

I don’t think your mechanic is doing all he can re. water.
First, is the water mixed with coolant, or Oil or fresh.
Did he pressure test the cooling system, crank case, engine?
The cost of a replacement motor and installation will be more than the car will ever be.

Thanks for the response. I will ask these questions. I would really like to keep this one because of all the things I have had done to it: front and rear sway bars, put in a 5 speed manual transmission, etc. A rebuild is out of the question.

Now I see it makes sense to restore.
You’re already down that rabbit hole.
There should be quite a bit of pre facelift lumps around.
What part of the world are you?

I am in the Middle Georgia area. There use to be a really good mechanic in the Chamblee-Tucker area but he is not there anymore.
Again thanks for trying to help me out.

I think that Coventry Motors is somewhere near there.
They have been a Jaguar problem solver as long as I know.

I have done business with them in the past. I check in with them off and on to see if they have an engine available and I have asked them to get in touch with me if they come across one. So far nothing.



Hi I have a '83 V12 with 63K miles. I’m in Maine. Ran good, plan 2 replace with a V8. Will sell 4 $2000…Jim

Can you send some info on it so that I can give it to my mechanic? Like service records, etc?


I have little info as I recently bought the car to do a BB transplant. Previous owner used car for summer toy for years, but started transplant as car would sometimes die when hot, and not restart for a half hour. When I got the car, it turned over with good compression, but had fuel feed problem. Thats really all I know…Jim


I will talk to my mechanic about the overheat shut down and see what he thinks. If you don’t mind me asking, why are you transplanting engines (going to V-8, etc)? And would you mind taking a picture of the engine (just a top shot) and emailing it to me at: jeptha46@gmail.com



Hi…Doing transplant as A carbuerated engine with a simple ignition is very easy to work on, and I like easy. Engine looks like every other jag V12. I don’t have a camera 4 a picture…Old guy…Old school. If it is really an issue, I can have a friend send you one…Jim

Jim, Thanks for your reply and I am sorry that I am so late in responding. What engine did you transplant in your Jag? I am now ready to get mine taken care of. I have been in touch with John’s Cars (johnscars.com) in Texas. They have the complete conversion kits for the Chevy small block or big block engines. My mechanic has a V12 available for $2,500 but I am thinking of getting the Chevy engine (small block). They say it is 400 lbs lighter (new springs for the lighter weight come in the conversion kit). They have a 3 speed auto transmission but I will try and keep my converted 5-speed manual. Just checking in on you to see what you did, with what engine and how it turned out.

I am in Columbus, have you talked to Dick Maury at Coventry West up in Lithonia they part out a lot of Jags and do some work also. They put a Five speed in my E-Type and have finished some lumps, you should be able to get good info from them.

Dan, Thanks for your reply. I have used Coventry West over the years but not for this project. My mechanic has come across a used XJS V-12 that he is checking out for me but I am thinking of going to the Chevy V8. Just confused if I want the 350, 400 or LT-1. Have you heard any results from these conversions?

Lots and lots of info out there. This might be a good place to start.


Thanks Jerry! I have been in took with them and have read about their conversion kit. I am pretty sure that I am going to go with John’s Chevy small block full conversion kit. Still trying to figure out if I want the Chevy 350, 400, etc. and if I want to keep my manual 5 speed or just go with his 3-speed auto.

Hi Jep-
Here are a few thoughts:

This whole conversation might be better suited for the Lumps forum, there are certainly experts there.

After a quick glance, John’s site seems focused on the pre-LT (and thus pre-LS) Chevy engines. I’d be curious why one would not go with an LS, they are an all-around more modern and better performing than the previous generations. More detail: https://en.wikipedia.org/wiki/LS_based_GM_small-block_engine

If for some reason you are set on going with an “Gen 1” engine, avoid the 400. To get the 4.125" bore into the same sized block as the 350/327, the cylinders are siamesed together which leads to cooling issues. Stick with the 4.000 inch block family. If I was doing a Gen 1 engine for the XJS, I would build a 383, which is block from a 327 or 350 (4.00 in bore) and the rotating assembly from a 400, giving increased stroke and a better torque profile. It’s been done thousands of times with great results.

Also avoid the 305. While external dimensions are the same as the 350 and the 400, it was an “emissions engine” from the start with many design compromises.

Unless you have medical or other issues which prevent you from shifting your own gears, I don’t know why you would not keep the 5 speed. A 3 speed auto box is a big step backwards, IMHO.

My .02 :slight_smile:

I have a couple of Jaguar V12s. I am just South of Pittsburgh. Contact me off list and we can discuss 412-853-1612.


Thanks Bob this helps a lot and I will take a look at at the Lumps forum.