In 1973, the carburetor V12 was first introduced in the XJ sedan and Car and Driver observed 9 to 11.5 mpg. The first model with fuel injection was the ’75 XJ12C and AutoTest found a 21% improvement in fuel economy (some was due to higher gearing).
The 70’s fuel crisis forced Jaguar to implement a completely revised head and piston arrangement in 1981 commonly referred to as the HE (high efficiency) version of the V12. On the “urban cycle fuel consumption test” the HE XJ12 improved 25% from 12 mpg to 15 mpg.
No matter how you look at it, the V12 is a thirsty beast. And because you are getting as much joy from your V12 Jaguar as possible…..your mileage will probably be worse than quoted above.
What does fuel consumption look like in real life (leaning toward sporty) driving? I have mentioned before that I am a bit of a nut when it comes to cars, so you may not be surprised to find out that I have been keeping track of all the gas fill ups through my 20 years of ownership.
The car typically ran between 10 and 12 mpg and very recently between 12 and 13 mpg. Its hard to believe I am getting excited about 13 mpg, but I think my tuning and upgrades have helped the car become more efficient.
Lets put this in perspective. According to PEW, the average passenger vehicle mileage in 1975 was 13.5 mpg, so maybe my 10 – 13 mpg is not so bad for a high performance sedan from that period.