Here's a short byuer's guide that includes the Ser III models:
http://www.jag-lovers.org/xjlovers/xjbuyersguide.html


Here's some tech info that'll give you an idea of what your in for:
http://www.jag-lovers.org/xjlovers/xjfaq/index.html


This is a longer and enjoyable wrire-up on the Ser III models. Worth reading.
http://www.jag-lovers.org/xjlovers/info/jagcare3.pdf


These are great cars. Built like tanks, drive like velvet. "The most modern of all antique automobiles".

Most repairs are well within DIY parameters and parts prices are reasonable.

Paint-chrome-leather-wood are where the big money is. If you care about that stuff it's best to find a car that doesn't need work in those areas.

Unless you are extra careful and find (and pay for) an exceptional example, plan on spending a chunk of money and time getting everything up-to-snuff. Once you've done that these can be very reliable cars.

Cheers
DD

 

The six cylinder engines crack between the bores at the top of the block. I had this with my 1980 car. This causes frequent head gasket failures as the block sinks were it is cracked thus removing the clamping pressure of the cylinder studs.
I rebuilt my engine around an uncracked block, but be warned, 8 out of 10 of the blocks are usually found to be cracked. I then had no more engine problems, but lots more other ones with the car!!

This cracking is due to Jaguar always doing things on the cheap, and trying to extend the life of the engine design which was produced from 1948 to 1986 ! The engine started life as a 3.4 litre but as time went by, more torque and power were needed so the engine had to be made bigger resulting in a 4.2 litre but still with the same block size. The bores were siamesed on the 4.2 engines, and on later engines, to improve cooling, Jaguar machined passages to allow coolant to cross the block between the bores. Trouble was this machining was done from the bores, making each bore look like a 2-stroke engine! So to make things good, the coolant passages were then covered by a thin lightly pressed-in liner. Over time the metal "bridge" at the top of the block between the bores cracked due to thermal stress.

It is possible to cure the problem by using "top hat" liners. These have a lip at the top which fits into a machined space, thus closing off the crack, (adjacent liners are made so they almost touch each other). The block face is then faced off to make it all smooth and ready for the headgasket.

 

I would recommend avoiding a car that has significant rust unless it already runs and drives good, then just treat it like a beater. Don't pour a lot of money into a rust bucket when you can buy a pretty good rust free fixer upper for fairly cheap. Personally I would always be bothered by the rust I knew was there, even if the outer appearance was brought up to par.

My car was $1200 and it needed only an ignition switch to run, but I decided to go through and fix a lot of neglected items before I put it back on the road. I have replaced the rubber fuel lines and vacuum lines (very brittle 1987 originals) to prevent future problems, and touched up some minor paint problems. The brake fluid leaked from bad reservoir-to-master cylinder seals and caused the paint under it to come off. I had to replace the brake booster anyway so while it was off, I cleaned that area to bare metal using an angle grinder and repainted it with Duplicolor wheel paint that was a decent match.

Also, I drained the gas tanks and cleaned out the sediment in the bottom of the tanks. Found a slight leak in one tank-- I sealed with Seal-All. Repaired the fuel gauge senders in the tanks that had a lot of built up scale deposits.

Still need to replace ball joints and tie rod ends, and assorted suspension bushings.

That is an example of what these cars typically need when bought at cheap prices. Rust costs a lot to fix properly, and the cars are not all that valuable at the moment. Come to Texas and find a clean one, or California/Arizona. Then you might have to repair some interior issues, which is easier than rust repair. I had some peeling wood trim, a broken horn, sagging headliner and other minor trim issues as well.

Do the research first, here and on jaglovers, read the online books for a good picture of common issues, costs, and solutions.