Ford Ranger - Cracked head after dealer returned it with no cool - pub landlord

Dear John,
I have a 52 plate Ford ranger with 52000 miles on the clock and full dealer service history.
In May 2004 it was in the local dealer for some accident repair it was insured with Ford. After the repair I collected it from the dealer and set off home only to find after 12-15 miles that the temp gauge had gone in to the red. I stopped and found that the dealer had not put any coolant in the engine.
I wrote to Ford and the dealer to put them on notice that I was concerned that it may have damaged the head and could cause a problem in the future.
The Head has now cracked and Both Ford and the dealer are denying any liability and are being very un helpful.
I am aware the over heating occured 6 years ago but the Ranger has only done 52K.
The dealer is blaming the Mazda engine claiming they have a none fault.
Thanks for your time and any help you can suggest

Paul Batten