jordanturbo

I keep a log book for my car and receipts. I record my milage at the beginning and end of each day. Whenever I stop for gas I keep the receipt, and log the date, milage, and amount of fuel I put in the vehicle etc. then I reset the trip counter, so I will see there how many km's I get each tank as well. I have done this for pretty well every vehicle I have owned, especially when it is for a company vehicle I own that sees occasional personal use so I can accurately calculate what I am allowed to write off as business expenses. I dont care about putting gas in my car I just like to track what milage i get, it is a personal habit, plus I find potential purchasers love documentation like that

RF5BPilot

No matter how drunk you get, this should still sound like nonsense.

RF5BPilot

In colder weather, you can get more hp with denser air. On the other hand, the newer fuel systems should adjust for changes in air density--so cold air alone is should not lower fuel mileage (as you'd simply depress the accelerator less for the same result).

Causes of reduced fuel mileage include the longer times people let their cars warm up before they drive (even if it's just the time for scraping windows), the more fuel it takes to bring the car to operating temps rather than just locomotion, increased drag from cold lubricants (less the engine oil, more the transmission, wheel bearings, etc.) and in poor weather conditions, drag from rain & snow on the road.

And yes, I own a Porsche and keep detailed logs of fuel mileage -- which is often an early warning indicator of problems in an engine. These are efficient cars. If it's not running in the way I'd predict, I want to know why. A good log can indicate subtle, long-term trends.

Macster

Agreed. I do not have a combined use vehicle. My vehicles are for personal use only. But I long ago was told by mechanics to keep track of fuel consumption to possibly spot a problem flagged by an unexpected/out of character change in fuel consumption.

Macster

The cold dry air represents more ideal climatic conditions for engine performance.

While the basic oxygen content stays the same colder air is denser and with less humidity (moisture) there is more air in the combustion chamber.

The DME recognizes this via the MAF and adds more fuel to keep the relative air fuel mixture the same.

As a result the engine experiences a bit of a hp bump.

One can experience something close to the opposite by driving in extreme heat or at altitude. It is more noticeable the quicker the altitude change takes place. I have experienced this by driving east on I-40 from the CA/AZ state line where the elevation is around 600 feet above sea level. Around 190 miles later (a bit over two hours later thanks to AZ's 75mph speed limit...) I'm crossing the divide at an altitude of around (IIRC) 7700 feet. My NA car's engine is not laboring (a few more K feet will have it laboring though) but it is down on power. Thankfully so is almost every other vehicle so performance stays relatively the same.

Imo000

Then why do the Snowbirds, practice in the winter. Ask anyone thaf flys how nonsense this is.

BruceP

Not really on point. Dense air is good for lift (ask the guy whose helicopter fell into Bin Laden's compound). That doesn't have anything to do with combustion.

That said, for entirely different reasons, internal combustion engines do like cold air because of the combination of higher oxygen density (at a given altitude, obviously) as well as its contribution to lower operating temperatures. Both of these are capitalized on further with an adaptive ECU that can adjust mixture accordingly.

Pesonally, I don't think this is a solvable debate. Oil companies reformulate fuel for the winter, which can affect energy content. An empirical win, here, would be pretty difficult.

Imo000

I'm not talking about combustion but air resistance. Denser air is harder to cut through. At highway speeds this is significant enough to add to the decrease in fuel mileage.

BruceP

I guess I have to tap out at this point. Over my head

Seems to me, for all intents and purposes, that would be zero sum combined with the better engine efficiency. But I even I - nerd of nerds - don't keep that careful track of my fuel economy!

Flat6 Innovations

Don't forget that most all areas of the U.S> have summer and winter fuel blends. I have seen a 5% change in MPG just from this on my engine dyno. Just from testing my engines I can tell exactly when the fuel blends here have been swapped in BSFC of the engines.

RF5BPilot

Sorry. My original reaction was unnecessarily harsh.

I am a pilot. I've flown since 1978 and own an airplane--so I'm not completely ignorant about these issues.

If the air made it harder to fly (by creating more drag), then why would the Snowbirds practice in winter? (Although I suspect they practice all year long.)

It is true that denser air would produce more drag. But the difference in drag on a car between a hot and cold day at anything like normal speeds would be negligible.

Again....sorry for being rude and abrupt.

jordanturbo

What are the differences between summer and winter blend fuels? Aka what additives are used to make them. I would have assumed something like ethanol, but the shell v-power I use says no ethanol, so I assumed their gas is very consistent.

I have not done any data logging on my p-car, but data logged quite religiously in my STI. In winter time I noticed that I was getting worse gas milage but assumed that it was because of idling and such since I noticed little difference in knock, timing retarding etc other than the minor discrepencies that could be allocated to quality control.

Hurdigurdiman

I think Porsche are specifically referring to an air cooled engine and not to the water cooled ones of today. I know having owned many VW beetle cars and a couple of Vans that they wanted the drivers to start the car and move off as they could over heat when standing around ticking over. I think it's good poilcy to let the modern water cooled cars warm up some before driving off. Especially during the cold winter months. Another thing is that most are manually geared cars and can be over revved quite easily. Over revving on a cold engine is a deffo no no. Not so with the auto cars. You can't over rev an automatic car.

Hurdigurdiman

I too am a Recreational pilot and know that cold air produces more lift causing the plane to achieve 'lift off' at slower speeds. Cold air most put the drag up some which needs more juice to get the car up to a particular speed, so less miles to the gallon in the winter. Correct? That being said... I am referring to Sea Level reactions. Higher levels, thinner air, equals not much drag and more miles to the gallon....Where the hell is this topic going lol.... Come to think of it, what was the topic anyway haha.

DBJoe996

Fascinating discussion! For what it's worth, I live in Florida...so when it cools down I get better gas mileage because I can turn off the AC. LOL! I love the little bit of extra oomph I get without the AC running.