MPG in summer

[Ashm3_uk]

I drive a Alfa 159 as my daily driver. My M3 E93 is my occasional toy along with my Ducati 899.

When topping up fuel I use an app which allows me to fill up pay on my phone without having to go in to the shop.

The app allows me to make a note of the mileage every time I fill up.

I've noticed in the summer I constantly get 60miles extra per fill up on the Alfa 159 (diesel). And about 30miles extra per fill up on the BMW.

I use the same fuel every time. Always fill the tank. Always reset the speedo as soon as I fill up.

Driving habits are the same all year round. Same routes etc.

Thoughts?

[Chris_Penning]

How much data do you have? Just one year?

[330ciprem]

Expected.

In summer your engine isn't working too hard to keep the temperature at an optimum level for combustion.

In winter it needs to work extra hard to keep the temperature up.

Good Example - You will notice dropped MPG if your thermostat fails. When in the fail mode it's set to the fail-safe mode of always open which makes the engine work harder thereby increasing the fuel consumption.

[hungryhippo]

In California, winter and summer gas have different specs and summer gas gets you better mileage. Can't speak for other areas.

[330ciprem]

Originally Posted by hungryhippo

In California, winter and summer gas have different specs and summer gas gets you better mileage. Can't speak for other areas.

That too is a contributor.

Winter gasses vaporize easily and summer gases don't (quick vaporization leads to higher emissions).

[XKxRome0ox]

one more factor for better summer mileage (at least for me living in a major city) -
slightly less traffic during daily commute

school is out
people are on vacation
so the daily commute is a little lighter than other times of the year

[streetpro]

...and you drive generally slower in the winter due to the road conditions... :-)
It is a fact that you have to heat up the engine - heat has to go into the metal... plus the friction is much higher when cold... the more cold starts, the lower MPG you get... I used to commute the very same way over a year with the same car... at summer I got some 10-10,5 while during the winter it went to 11-11,5 liters/100km

[Ngilbe36]

This also has to do with the air temperature. When the air is warm, it is less dense and your engine compensates for less air with less fuel. You lose power but gain economy.

[SLC Steve]

The biggest factor for where I am in Salt Lake is the winter blend gasoline. It is watered down so badly. I don't drive my M car in the winter but the other cars that see winter duty see at least a 10% drop in economy.

[Helmsman]

Originally Posted by streetpro

...and you drive generally slower in the winter due to the road conditions... :-)
It is a fact that you have to heat up the engine - heat has to go into the metal... plus the friction is much higher when cold... the more cold starts, the lower MPG you get... I used to commute the very same way over a year with the same car... at summer I got some 10-10,5 while during the winter it went to 11-11,5 liters/100km

With the M3...?!?

[Mvy]

Op is in the UK. But for us in the USA, its prob mostly to do with the change in formula from summer to winter. See this article:
https://auto.howstuffworks.com/fuel-...ummer-fuel.htm


Twice every year in the United States, the fuel supply changes. It's known as the seasonal gasoline transition. This change is the biggest reason for the price hike in summer gasoline. Depending on the time of year, gas stations switch between providing summer-grade fuel and winter-grade fuel. The switch started in 1995 as part of the Reformulated Gasoline Program (RFG), which was established through the 1990 Clean Air Act Amendments. The Environmental Protection Agency (EPA) started the RFG program in order to reduce pollution and smog during the summer ozone season, which occurs from June 1 to Sept. 15.

In order to reduce pollution, summer-blend fuels use different oxygenates, or fuel additives. These blends, the EPA claims, burn cleaner and also help compensate for a limited oil supply. The EPA says this practice of using seasonal blends also encourages the development of alternative fuels.

So what's the difference between summer-grade fuel and winter-grade fuel? Summer-grade fuel is more expensive for two reasons -- because of the ingredients it contains and because refineries have to briefly shut down before they begin processing it. Summer-grade fuel also burns cleaner than winter-grade fuel. This just means that it produces less smog and releases less toxic air pollutants.

[SkiFly01]

Originally Posted by 330ciprem

Expected.

In summer your engine isn't working too hard to keep the temperature at an optimum level for combustion.

In winter it needs to work extra hard to keep the temperature up.

Good Example - You will notice dropped MPG if your thermostat fails. When in the fail mode it's set to the fail-safe mode of always open which makes the engine work harder thereby increasing the fuel consumption.

A failed thermostat (failed open) will cause a decrease in MPG's because the ECU will go back into a warmup routine if the engine temp drops enough, aka extra fuel to increase engine temps quickly to bring it into a recommended operating range. So your AFR's will be way off.

Now the winter/summer engine working easier is the opposite of your statement. If your statement were true turbo cars would run without an inter cooler to keep the increased air temps. Dynographs show the same cars in winter temps perform better than those in summer or extreme high temps. An engine will not care that it's well below freezing for ambient air temps, in actuality it will be more efficient because the air is denser and the radiator will be more efficient as heat dissipation. The delta for heat transfer is greater.

[Scharbag]

Originally Posted by Helmsman

With the M3...?!?

Exactly what I thought. Only on really long highway drives do I get anywhere near 11L/100KM. In the city, I average 20+L/100KM...

Argh.

[Helmsman]

Originally Posted by Scharbag

Exactly what I thought. Only on really long highway drives do I get anywhere near 11L/100KM. In the city, I average 20+L/100KM...

Argh.

Did a 1k km trip last week majority stable high way at 90-120km/h, still 13L/100km.... soon as one touch the pedal for a take over or two the numbers sky rocket. Still keps around 16L average including plenty daily commute so fair enough I guess..

[330ciprem]

Originally Posted by SkiFly01

A failed thermostat (failed open) will cause a decrease in MPG's because the ECU will go back into a warmup routine if the engine temp drops enough, aka extra fuel to increase engine temps quickly to bring it into a recommended operating range. So your AFR's will be way off.

Now the winter/summer engine working easier is the opposite of your statement. If your statement were true turbo cars would run without an inter cooler to keep the increased air temps. Dynographs show the same cars in winter temps perform better than those in summer or extreme high temps. An engine will not care that it's well below freezing for ambient air temps, in actuality it will be more efficient because the air is denser and the radiator will be more efficient as heat dissipation. The delta for heat transfer is greater.

Generally turbo out temperatures are north of 200F (extremely vague assumption btw). Atmospheric conditions can't replicate the efficiency of an intercooler in those cases.

You are right. Dynos show higher power in winter but they are warmed up cars already. And you are talking about a 30 second run. On a highway you have an engine that needs to work first to attain that temperature and then keep it there. That is one of the reasons why winter gas has more energy than summer gas.

But then again my opinion would be little biased - where I have lived the temperatures in winter hover around -20 to -30C.

Cheers!

[SkiFly01]

Originally Posted by 330ciprem

That is one of the reasons why winter gas has more energy than summer gas.

The difference between summer- and winter-blend gasoline involves the Reid Vapor Pressure (RVP) of the 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.

https://newsroom.aaa.com/2013/06/wha...lend-gasoline/