Hi all,

 

I have an issue with my daily drive that I thought I would post on here, as the people on here are far more intelligent than on any other forum!

 

A couple of months ago, I bought a Jaguar S-Type 2.5 V6 Automatic to replace my E-class that was sadly written off over Christmas.

 

The Jag is in mint-condition (probably the cleanest used car I have ever seen), fully dealer serviced and clearly lovingly cared for. It also had only 46,000 miles on the clock.

 

The problem I have regards it's fuel economy, which is beginning to matter more and more as each day passes.

 

It is supposed to return 32-34mpg on the motorway, and many Jag drivers have confirmed that they even get 37-38 on the odd run.

 

This would make sense, as my E-class used to give me 30-32, despite having a larger engine (2.8), being heavier and having 180,000 miles on the clock.

 

My Jag however is giving me 27 mpg - consistently. I have now done nearly 2,000 miles and the results are consistent.

 

Despite the excellent condition and service history, I have personally checked the oil, air filter, brakes, switched off air-con etc. and cannot find anything obvious. I even visited a dealer, but he wasn't any help.

 

Any ideas what could be the problem or what I should check next?

 

20% more fuel/less mileage is a lot in my opinion...on a full tank of 15 gallons, it's equivalent to over a 100 miles!

what are the tyres like? cheap ones or good ones?

Tyre pressure?

Tyres are new Michelins, 235 17"

 

The standard 2.5V6 has 215 16" tyres...could the difference in tyre size make that much of a difference?

 

The thought had crossed my mind but the brochure has both models (SE and Sport) showing the same mpg.

 

How much difference would larger and wider tyres make in reality?

I put 18's on my old 530i that came with 17's. That knocked about 5mpg off!

I put 18's on my old 530i that came with 17's. That knocked about 5mpg off!

 

Ouch! :cursing:

They were replica M5 wheels, made of cheese to i took them off.

If your wheels were on the car from new, i cant see that doing it..

They were replica M5 wheels, made of cheese to i took them off.

If your wheels were on the car from new, i cant see that doing it..

 

Yes, they're standard wheels. It's the sport model, which comes as standard with 17" wheels and 235 rubber. That said, surely it must consume more mpg compared to 16" 215s?

 

7mpg seems extreme though.

Could the fuel mixture be too rich?

Try some injector cleaner..

I think the main question is how do you drive it?

I think the main question is how do you drive it?

 

Very true, if you are trying to achieve the brochures apparent MPG figures, they are done under the best possible circumstances, and are unlikely in real life, especially if your not 99 years old and actually have a right foot that works :)

I think the main question is how do you drive it?

 

Good question, but on the motorway, there isn't much choice. Cruise control at a steady 70mph...

The thing is, I've also tried 50mph to see what happens, and no improvement.

How are you calculating your MPG figures?

Are you relying on an on board reading, or working it out manually?

If its the computer, have you checked the figures yourself?

have you changed the fuel filter?

 

I haven't personally but it was changed at the last major service.

How are you calculating your MPG figures?

Are you relying on an on board reading, or working it out manually?

If its the computer, have you checked the figures yourself?

 

I've always calculated the mpg manually, as the on-board computers are typically optimistic by 2-3 mpg. That said, it's not bad on this car, being only 1 mpg more than reality.