I am just coming off the first leg of my road trip to Atlanta for Christmas.

Ambient temp ranged from 40-53 degrees.
Speeds were 80-85 mph

My gas mileage dropped from about 28.5 (that's what I used to get in the summer) to about 23.8 at about the same driving speeds.

I can see maybe a mile or two less, but this is almost 5 mpg less.

The only change is that I have my new tires on the car.

Anyone else experienced this?

 

Mine always drops in the winter...

Maybe it's the fuel your using..

Scaring myself regarding ethanol in fuel, I just changed gas stations that I use.. My MPG so far on this tank has improved by 3MPG without any change in driving routine or weather conditions...

 

It is not uncommon for new tires to cause a significant drop in mpg. Some tires have a far greater rolling resistance than others. You recently put on a set of Bridgestone Serenity tires, correct? You may want to do some research to see if others going to this same tire have reported a similar drop in mpg....

Another potential contributor to lower mpg is higher concentrations of ethanol in the fuel you're buying. You were on a road trip so I assume you were buying fuel from highway gas stations that you don't normally deal with. Check the ethanol stickers that are required by law on the gas pumps before you buy....

 

I'll have to check on that. I think that I may have gotten a bad tank.

I don't believe that I have ever driven the beast in weather this "cold."

 

Very good points. I will check into that. When I was doing my research before, I never saw any reports on gas mileage drops. Hopefully this will change.... Gas is getting kind of high lately.

 

Also, check your tire pressure. The owners manual (or the sticker on your drivers door frame) probably says to run 30 or 32 psi in the tires. That's because "luxury car" companies know that their clients like cushy, soft rides. But they don't care about tread longevity or gas mileage....

I run our S-Type tires at 34 to 35 psi year-round, and I check that pressure every weekend. My wife consistently gets right at 34 mpg on her trips to and from Tampa running 72 to 74 mph on cruise control with the HVAC system set to whatever is comfortable for her. In fact, she's on I-95 North headed back home right now....

 

I will definitely check that out. 34 mpg? Incredible!!! Is that 72-74 on the speedo or on a GPS. The speedometers are about 3-4 mph optimistic from what I have seen.

I got 30-31 mpg on a long trip once measured off the trip computer. That was in teh summer with my old tires. I drive 80-85 mph overall. I use AC sparingly.

 

Several factors. First, ethanol content of the gas - a lot of the "winterized" blends contain up to 15% alcohols.

Second, the tires can play a role. Pressure, and actually rolling diameter and unsprung weight.

Lastly, Ambient Temperature. - The cold air rushing through the motor makes good power compared to less dense air but with a corresponding increase in fuel consumption. Also the colder ambient air actually pulls more energy away from the motor as far as taking heat away from the motor.

George

 

I think there may be another smallish apparent amount of reduced mpg as follows:

If you habitually set the cruise on a particular speed (as I do), bear in mind the way the car "knows" the speed: it calculates it from what it believes to be the tire size. Your tires are now bigger so at the same indicated speed (as before the tire change) you're now going faster. That'll mean the various mpg calculations the car does are off by a little (compared to what they were) but also because you're going faster there will be a little more air resistance (consuming a little more fuel).

I can't figure out what percentage those result in! Anyone want to estimate it please do

 

That's 72 to 74 mph on the speedometer using cruise control. Had the Jaguar dealership sales guys tried to tell me that this car would average 34 mpg on these trips back and forth to Tampa to visit her parents when we purchased this car just over two years ago primarily for that specific purpose, I would have called them liars straight to their faces. And after a couple of those trips had been completed, I would have had to apologize to them....

 

34-35 is about the limit as far as tread longetivity, because after that, you will wear out the center of the tire before the edges. I have NO idea how you get mileages in the high 20's. My car has NEVER gotten past 23 mpg mixed daily driving. I once got 26mpg and change on a straight shot run from eastern pa to the jersey border, almost 400 miles non stop.

Maybe it's just a combo of the traffic conditions and my heavy foot. https://www.jaguarforums.com/forum/i...cons/icon6.gif

George

 

It depends on the vehicle as well as the tire. I run 37 to 38 psi in the 18-inch Bridgestone Alenza tires that are on my wife's 2004 Lexus RX330 AWD. That car sees more of a mix of highway and city driving, yet the Alenzas routinely get 55,000 to 58,000 miles before they're done on that vehicle. And they wear evenly across the tread, no centers worn out first....

On my 1999 Dodge Ram, I run 33 to 34 psi in the truck's 16-inch Firestone Destination LE tires. The 5.9-litre V8 is tough on all tires, but I can generally get 45,000 miles out of them before they're done....

The key is to check your pressures weekly and rotate your tires relatively often. On all of our vehicles, I rotate the tires at every oil & filter change....

 

Some tyres have a high rolling-resistance because of the rubber type used. But they also have a fantastic grip on the road and will provide a short stopping distance. I believe this type of rubber is also used for better traction in snow. There is of course a penalty, isn't there always? That shows in a worse fuel consumption. Some of the cars in UK have just scraped into a cheaper road tax band by the makers simply using "eco" tyres which have a good rolling-resistance, but poor braking distance. This produces a little less CO2 in the grams/Km. rating.
My diesel S-type is only doing 25 to 26 mpgUK in the current very cold weather (was minus 18 in some parts of Yorkshire). This has two parameters:-
1) It's a diesel, notorious for taking a long time to warm up. But you can't have it both ways, the economy is due to less wasted heat from the fuel burning.
2) Most of my journeys ATM are short, 10mile or less, and the engine is just warmed up by the time I get back home. Bugger.
So...I've realized that the only way to get round this cold running problem is to warm up the engine by some other means before even switching it on. This would have far more effect than things the makers have done, like having 6 or more gears and a continuously slipping torque converter clutch. I shall devise something, but it won't cost £250 to fit, it won't use heavily and multiple-taxed diesel, and it won't cost anything to fit, and it WILL be cost-effective. Just watch this space, as they say.
Leedsman.
p.s. The S-typeD has shown no problems at all this very cold weather. Starts first time every time. Autobox working and changing as usual. Getting it ready for MOT (the british annual government safety check) I found only a blown front sidelamp. Dead easy to change, unlike a current Renault, where you have to find a child with a small hand to fit a lamp through the orifice provided.

 

Uh yeah until you get staggered STR Vulcans with directional tires and have no way to rotate tires...

George

 

Sorry George, but that would never happen to me. I won't buy a vehicle on which I cannot rotate the tires....

 

Not all states require that sticker.... Florida does, Ohio does not..

Follow the link in post #19

https://www.jaguarforums.com/forum/s...ad.php?t=47204

 

That rules out a LOT of interesting cars! (Because they are RWD with wider tires on the rear.)

 

Wow - I don't know what to tell you to check, but my STR averages 26-27 MPG all-highway (most recently a trip to NH, then Boston, then back to DC). I even averaged 24MPG on a 5-hour trip that should have taken about 3. I would expect the 3.0 to average much more, so there might be something wrong?

 

Car is perfectly fine. Everything runs fine. No CEL's codes etc. Believe it or not, the 3.0 is probably the least fuel efficient S-Type.

3.0 - 16 City 24 highway...

http://www.fueleconomy.gov/feg/2008c...f.jsp?id=18665

Now, my drive is probably 50/50 mixed maybe a bit more city side because of traffic, and like I said, my foot weighs as much as a bowling ball. I've honestly never really cared about fuel economy, but some of these reports just have me amazed. I've gotten 26, 27 on the highway on a straight cruise, but we never have a highway open long enough to really get true highway mileage ratings here in Jersey.

My morning commute:

1.6 miles of local roads (25-35mph).
6 Miles of Interstate 195 - 50 - 60 mph depending on congestion
27 Miles of the New Jersey Turnpike (I95) 50-90mph, cyclically up and down (as you approach exits etc). This is on a good day.
3.2 miles of Rt18. The first 2 miles are generally bumper to bumper, and the other 1 is usually 30-40mph in congestion once 18 splits into local and express sides.
.5 mile of local Surface streets. 25mph between lights.

My Evening commute. - I take a different route because the Turnpike is literally congested the entire 30 miles south.

Same .5 mile of local surface streets 25mph between lights.
2.5 miles of Rt18 - Generally entirely bumper to bumper
4.6 Miles of Rt1 South - Generally about 40mph with moderate congestion
31 Miles of Rt130 south - 30-65mph cyclically, depending on congestion, and how many lights you get caught at.
1.5 miles of local road 45mph.

This is a Normal day, with no anomalies or abnormal traffic conditions.

See why my car gets the mileage it does?

George

 

Gas gauge/computer issues ... ? When I is was researching the mileage potential for an STR on here they ended up a lot higher than I've ever observed on highway driving. Even the indicated gas mileage never got as high on my car. My car runs very nicely but it never idicated over 21.7 mpg and really ended up being 20.1 or so.

Ethanol contains less energy and there's plenty more of it in winter blends depending upon where you are in the country. The morons at the EPA want to go with even a higher content in spite of the vast potential technical issues. It's also using valuable farmland for fuel. Dumb in so many ways.