Jaguar Repair: overheat&nonstart, 12 cylinders, combustible fuel

Question
my 84 XJS v12 was overheating on my way home. The next morning  it would only turn over. What is the toubleshooting sequence for it. I would start that the amount of fuel is ok . also I changed thermostats a week previous and I was looking to see possible causes for overheating.    thx

Answer
If it overheated and now does not run, you need to address the  not running first. All engines only require 3 things to run. Compression, fire and fuel, with conditions on each.
You first need to confirm that the overheating did not do any engine damage by doing a compression test on ALL 12 cylinders.
Be sure to disable both coils (you don't want a spark jumping down a coil tower and destroying the ignition system. Remove all the plugs. Block the throttle open. You must see 125 PSI or above to expect it to start. 100 or below will not fire at all. You should see 150+. If any coolant blows out of any plug hole it is no use testing further.
If all 12 cylinders are OK and not more than 15% of each other, reconnect the coils and place each spark plug on each wire and lay each plug on a metal part of the engine and spin the engine with the starter and watch for a thick blue spark on each plug. Or you can reinstall all the plugs and connect a timing light on a plug wire and have someone spin the engine while you monitor the timing light to confirm ignition. Last is fuel, spray either starting fluid in each air filter or a combustible fuel in while someone spins the engine and if it fires up for a second, you know it is a fuel problem and will require a series of tests for the injection system.
Let me know,
Howard