I just want to know, is average 24-25 mpg normal? I drive about 80% highway.
I'm using a K&N air filter, and I just change my oil , oil filter, and fuel filter recently. And I have also alligned my tires.
Basically I have done everything to maximize fuel efficiency.
If this is not normal, can somebody give me some clue why it happens and how to fix it?
I'm really frustrated with the gas prices now, I have commute at least 60 miles/day.
Thank you.

 

You don't say which engine your S40 has.

I have a T4, the thirstiest of the 40 series engines, and average 30 mpg on high quality gas.

There are an awful lot of factors that can affect mpg/fuel efficiency, including:

Driving style (traffic signal grand prix will eat fuel, as will driving in too low a gear).
Automatic transmission gives reduced mpg, manual tranny gives improved mpg.
Condition/state of tune of engine & how well serviced. Includes condition of fuel system inc. injectors (some cleaner added to the fuel tank works wonders) and the ignition system inc. plugs.
Correct tyre pressures.
Getting rid of unnecessary weight - do you have stuff in the car that you don't need to always have in there?
Driving with roof bars or towbars still bolted on, that may only be used once or twice a year (or never).
The quality of the fuel used.
Driving with the windows and/or sunroof open burns more fuel.
Using systems such as climate control/aircon and electrical accessories such as lights, wipers, radio, heater blower etc. burns extra fuel because the engine has to work harder turning the pump & the alternator.

These are the most obvious things to look at, 24/25 mpg is more like stuck in city traffic figure rather than 80% highway driving figure. Hope you manage to improve mpg! Just think, you could be in UK & paying near to $8 a gallon.....

 

my engine is 1.9T, automatic trans and i'm using 89 octane gasoline.
So, that means there is something wrong with my car.

Thanks anyway, i hope i can work it out.

 

I'm guessing from the chart below that 89 Octane to you means roughly 92 in UK. This seems low, as Volvo recommend 95 RON (91 PON) for the petrol engines they put in the S40/V40 range (except the T4 where they recommend 98 RON).

In America the service stations use the Pump Octane Number or PON rather than RON. This is the average of RON and MON. This system can be abused by adding octane boosters to poor fuel though.

RON MON PON
90 83 86.6
92 85 88.5
95 87 91
96 88 92
98 90 94
100 91.5 95.8
105 95 100
110 99 104.5

Turbo engines tend to need/run better on higher octane fuel and the better an engine runs, the more mpg (and power) it will give. Suggest you consult your owner's manual or Volvo dealer for recommended octane rating for your US spec. car.

Do remember that using a lower than recommended octane gas will give reduced mpg and bhp and may cause pre-ignition of the fuel in the combustion chamber (pinking), risking expensive engine damage. Therefore you may find that moving up to 91 PON gas, whilst costing a few cents more, will in fact save you money with improved mpg and longer engine life.

Just a word of caution - don't expect instant results, because it will take several tanks of correct octane gas to run the 89 through the system and also, your car's engine management system will need to adjust to the altered octane.

Also recommend checking condition of air filter & spark plugs.

Would be interested to know if moving up a gas grade helps in the long run.

 

Ok, I will start using it. Thanks for your detailed answer. I like it.
I will let you know if there is improvement or not.

 

yes tell me about it $8 a gallon sucks. and u get about 26mpg on my 1.8xs 1999 S40. not sure why its so low. i to a lot of countyside driving about 50 - 60mpg 3rd 4th 5th gears a lot.

 

r2u-I have an 03 s40, AT, 27,000 miles, same engine as you, and get 37mpg routinely on the hiway, and 29 in town on 87 octane gas on a routine basis. I've had the car 5 months, run Mobil 1 10w-30, did a drain and refill of the tranny, keep the tires at 34#, and admittedly don't push the gas pedal hard. I agree with the above, and would check spark plugs, as I believe you should get much better mileage. Regards- Bill

 

A bit off topic but... - I saw a Top Gear episode where an Audi A8 drove from London to Edinburgh (AND BACK) at a constant, yet fairly slow speed of about 40 mph, ON A SINGLE FULL TANK OF GAS! That seems unbelievable...too good to be true!

 

I bought a 2002 S40 this year with 87K. From the beginning, I was impressed with the gas mileage and power. I do about 80% highway driving and average about 29/30 MPG.
I bought a scangauge (needed it for the CEL) and has taught me how to drive for the best mileage. I can get up to 34MPG on the highway and the worst tank I had was 24MPG with full load and lots of uphill driving. Working on getting better gas mileage (have a K&N and just installed better exhaust).