With my '03 XJR, (with 43K miles), on a 250 mile trip, with the cruise set at 75 MPH, I got about 18 MPG. This was double checked with a manual calculation, and the trip computer seems spot-on. My 99 XJR would get between 22-24 under the same conditions. I'm wondering if other 98-03 XJR owners are getting similar mileage? I probably wouldn't have been as surprised if my previous Jag hadn't done so well. Should I expect better mileage? If so, where would you start to determine the cause?

Thanks!

 

@j

'00 XJR. US Spec. No mods. Factory Pirelli specced tires. 96k miles. Shell V power.

Urban (means work and back, 10 miles on city streets with A/C on) = 16mpg

Highway (75~80MPH on cruise) = 23mpg

Highway on ramps (Sport mode selected, J gate in 4. Right foot in the carpet) = 4mpg :-)

A friend at work who does a lot of miles was doing an experiment with different gas stations and gas vendors and he has seen 10~15% fluctuations just by using different vendors. Costco being the worst (and cheapest). Not sure if that could be a factor in your comparisons to your older car? are you still using the same type of gas ?

 

My Bike runs like it's fouled plugs with Costco Gas. It was so bad I thought I had broken something. Next tank (Chevron), coughing/sputtering went away.

For me, I run Chevron, although, will use Shell in a pinch. I don't notice any difference between them though.

City: 16-17
Highway: 23

 

Highway 23 MPG is what I was expecting, and I have been using Esso Premium (Exxon) for the past 40 years. I can also get 4 MPG in sport mode . So obviously there's something wrong with mine. Any ideas on where to start to track it down?

 

99 XJR - MPG about like SARC (at least for the first 120,000 miles :-) - BP or Conoco gas - used cut-rate gas once and regretted it!
Usual suspects for poor economy: AIR FILTER, low tire pressure, first things I'd check. Then change fuel filter (very easy if car on ramps or lift) & run Techron or BG injector cleaner in a tank of fresh fuel. Clean part-load breather. If still getting poor economy put in fresh set of spark plugs. If still issues, clean the throttle body - excellent step-by-step for that here:http://maxperformancecars.net/, click on "Articles" near top banner.
What fantastic road cars these are, eh? Take the fatigue out long drives like no other I have owned.
Cheers!
________

 

Thanks very much, I appreciate the info and check-list. I'm running 26 PSI in front, 28 PSI in rear as per Jag manual. Do you feel this pressure is too low and contributing significantly to dismal fuel economy?

Cheers!

 

I noticed it relies very much on the gas you use and always recheck gas mileages with different stations whenever I get a new car. My 96 vandenplas only liked crap Texaco! I get about 18 mpg at those speeds too using bp or chevron, my mileage drops 2-3 mpg on other gases. I usually average 15.5mpg with a mix of city/highway driving. I also noticed that my parents 03 xj8 on average gets 3 mpg less than our 98 did when we had that in 2001, I blame this on the rampid use of gas stations adding ethanol into gas. Tire pressure does seem low check the drivers side door it should have recommended cold pressures listed. ++ On cleaning the throttle body and air filter, mine went up dramatically when I did, try cleaning maf too could help especially if using a K&N filter, reminds me I better do mine today its been awhile.

 

I second that!

I've noticed this also. I think it's the same thing as when you go to the grocery store and a bag of potatoes is now only 4lbs or 8lbs, instead of 5lbs or 10lbs, but you pay the same price, or more. They are adding additives to make gas cheaper to produce, but we get less milage, AND they keep raising the price. Not to mention the extra wear on our engines for using all the additives.

This should not be happening with gas companies though, because they still raise the price every time there is mention of a change in barrel prices.

 

My 99 xjr and 2003 xjr get the same...15 in town and 21 on the road. My trans fluid was a quart low on the 99, preventing it from shifting to 5th gear for a while, lowering the highway number to 18. When I figured out the problem with the fluid, it went back up to 21. You might very carefully see if you are shifting to 5th gear....

 

John:
My xjr quit getting into 5th. No other symptoms, so I was assuming I had some tranny work ahead of me. I hope your tip is whats wrong!

 

John, that's a great post, and something I hadn't considered when talking to Fairlane about tire pressures and such. Did you have any other symptoms, and was a there a DTC code logged (posssibly overtemp) when the fluid level was low?

 

I’m definitely shifting into 5th, so thankfully that's not the issue. I'm going to raise the tire pressures, and check the Air Filter. I'm a bit cautious about the fuel injector cleaner. First, I cannot get Techron or BG 44 here in Canada, and I don't want to do any damage. I'll ask my mechanic what he recommends.
Thanks to everyone for their words of wisdom.

 

There were other symptoms, the most bothersome was the shuddering upon letting the accelerator up after sticking it to the floor until the car hit about 80. Sometimes I would get a trans fault dtc, and more than once I did get a overtemp code. I read somebody's thread about how they had the same shuddering problem, and others theorized that the fluid ran out or foamed....So I started down that path. I got a dipstick from ebay for 25 bucks, and started adding fluid while the trans was hot (engine running in park). I got almost a full quart in the car by the time it hit the full mark. I have driven it for about a month now. It finally shifts into fifth, has not had a trouble code, and stopped the shuddering problem. So, not being one to let well enough alone, I have ordered a full change of fluid, gasket, and filter. This car has 102k. I will let you know if I screw it up. It is working perfectly right now.

 

AWESOME, thanks for taking the time to reply, we'll both be glad you did...

The most likely reason your fluid was low is that there is an electrical conector on the RF of your transmission which is leaking. This is a fairly common problem with the MB trans used in XKR/ XJR, there is a Jaguar factory bulletin on it.

It's a repair you can probably do yourself. PM me if you want more details. The parts are all available in stock at my local Benz Dealer, probably yours too. The cost for all the trans items, including the fluid, is pennies on the dollar compared to Jag dealer list.

Why I'm glad to read your answer is that I have performed these repairs before, but not yet experienced drivability faults caused by the low level. Now I have some information that will deter me from looking other places until I rule out the basics first. Thanks again,

Andy

 

Same tranny as MB? Awesome info, friend. Much help in determining where to get the best prices...

M5