2009 xc90 3.2 awd Better gas mileage in the summer but not in the winter WHY?

[chefmarkt69]

Hello everyone,
I have noticed that I get better gas mileage in the summer months as opposed to the winter months. I cant figure out why? I live in new England and I understand that in the winter months the gas is blended. Also I know I warm the car up longer but still it is a least a 100 mile difference. my 2005 Saab 95 arc gets the same mileage all year round. please help.

[Rattnalle]

I would say that's pretty normal but partly due to using winter tyres, don't know it you do. I've had cars where the difference was barely noticeable and others where it was though.

[chefmarkt69]

No winter tires used on mine, but I thought it might be a MAF issue or something along those lines?

[Masscomguru]

This is normal. It depends how the engines tuned also. I assume your Saab requires premium fuel which would contain more energy than regular and would even out the winter blend a little more.

[chefmarkt69]

Yes you are correct, only shell 93 v power for the saab. The Volvo I use shell 89 octane.

[tardcart]

my 850 gets 1.5 miles to the gallon more in the summer. this is I think is due to thermal efficiency which I don't understand but guess less energy is used to heat the engine to 198F. I hadn't considered that summer blend is said to be less efficient. It would be interesting to go to the air port and put AV fuel in with no alcohol or MTB and see what the milage would be, but we can't since that's got lead in it. I do use it for chainsaws and old cars that sit for years. it never goes bad and does not rot the tank. In a hundered years that car would start. one of the good things not yet outlawed by the gov. AV fuel. also it does not evaporate.

[abscate]

This is normal. It depends how the engines tuned also. I assume your Saab requires premium fuel which would contain more energy than regular and would even out the winter blend a little more.

The energy content of premium fuel is actually lower than regular grade, but it is small amount, something like 2-3%

[5ft24]

The colder intake air is denser and requires more fuel to stay at the proper mixture. hotter summer air is less dense, and requires less fuel for the same volume of air.

[jimmy57]

My vehicles get worse in summer than in winter. I never warm up a vehicle but when it is 100F out I start one and let it cool down before I drive off and I am likely to leave it running while I fuel up. My drive speed and congestion are pretty consistent year round with very rare winter occasions where driving is slow due to ice or snow (Texas).

[matthew1]

Winter fuel - "The US Environmental Protection Agency (EPA) says conventional summer-blend gasoline contains 1.7 percent more energy than winter-blend gas, which is one reason why gas mileage is slightly better in the summer." -- AAA

Winter warmup time -- time to get up to operating temperature is time spent outside of the best efficiency range of car engines.

In the summer air is warmer, requiring less energy to move through.