Perhaps in your country there is a red area, but for vehicles sold in North America, the engine temperature gauge has only a green zone to the right of the '90' marking. Compound that with the fact that many Americans are unfamiliar with the Celsius temperature scale as they still use the old Fahrenheit system for everything and there could potentially be some overheating issues to deal with.

Most owners in the U.S. have to deal with annual or biannual emissions tests, so most XJ6s are running with the 87 C thermostat to reduce NOx output. Unfortunately, the XK engine was never designed to run that hot, thus the loose tappet guides and blown head gaskets.

NBCat

 

I agree that you don't want to see your gauge moving above 95 degrees, however one interesting point to note is the following extract from the original Jaguar XJ/Sovereign "Series III Driver's Handbook" as supplied from Jaguar with the car (a.k.a. the handbook, in front of me now):

I almost had a heart attack when I saw 125°C being quoted as normal! The last time my Sovereign did that I needed a new head gasket!

Don't believe me? Go and turn to page 14 of your owner's manuals, and have someone ready to call 000/911/999/etc.