How much is your gas milage affected by the winter weather?

For those of you that actually have winter weather and drive your pcar in it, what kind of milage do you get in normal months versus winter months? Normally I get 400-430km per tank of gas, now that winter is around, temps are low, and I have to let my car idle for 5-10 min before it hits low idle and I move the car, I am now averaging 300-320km per tank so I am down about 25%.

Why are you letting it idle to warm up? Porsche is pretty specific that the best way to warm the car up is to drive it. They do not recommend letting it idle. I get in, turn the key, and drive away... If your drive is short enough that the car doesn't warm up then you'll see an impact in your mileage since the engine is less efficient when it is outside its normal operating temperature range. Otherwise your mileage should be pretty similar (if you stop letting it idle...)

I dont know.. But I swear my car runs so much better in cold weather. I dont mean smoother. I mean faster. A change I can feel in the seat on my pants...... and thats is worth 50% worse MPG

Just took a look at my fuel economy app, and it looks like temperature makes little difference in my 996. This is by contrast to my truck, for example, which immediately starts burning a liter more per hundred km when the temperature drops to freezing, without fail. Whereas the speed I'm driving the Porsche at makes a HUGE difference. I've seen 9l/100km and less on the highway, and as much as 18l/100km in city traffic... which is just awful.

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...and it is. cooler air is denser, denser air contains more oxygen by volume. More oxygen in, more power.... this is the theory CAI's are based on.

The denser airnis harder to push so, air resistance is up and so it fuel mileage. Also, the additives the refineries put in during winter, to keep their gas from gelling in their fuel depos, probably lower the mileage too.

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Are you sure about that 5 to 10 minutes to idle before idle speed falls to near normal? Can't believe it would take the engine 5 to 10 minutes to fall back to near its normal hot engine idle speed. While I do not often (anymore) get a chance to start my engines in real cold temps in either car the engine idle speed drops from around 1K to just under 800 in around a minute (or less) idle time. Since one car (the Boxster) is outside I have to let the engine idle longer to warm up the heater and clear the frost (Sunday) but today even though it was cold there was no frost and I was away in the car after the usual one minute or so idle time, just until the idle speed dropped and the secondary air injection pump shut off. Over the years gas mileage drops in colder weather by not quite 10%. Say the Boxster averages given my usage around 23mpg winter with the same driving route, and so on, has this down to 21.5mpg. Anyhow a combination of things contribute to the increase in fuel consumptoin in the winter months. More idle time mainly to wait for the heater to warm up and the frost to melt but sometimes from heavier winter traffic. The engine is colder and takes longer to warm up so the oil is thicker and there's more lost to the thicker oil's friction. Generally winter traffic is consistently slower traffic too so the car spends more time idling at lights and when moving moves slower than in the summer months. Which brings this up: I have no kids but for those people that do and give the kids a ride to the bus stop or to the school or to after school activities obviously this change in usage can play a role. Be sure you check tire inflation pressure. When cold temps set in tires that were inflated just fine for the warmer temps are very likely under inflated for the colder temps. Under inflated tires can really impact fuel economy. Last while I too notice that the engine seems to pick up some in colder temps this alone can't account for the increase in gas consumption. But of course I do rather enjoy the benefit of colder temps in this regard. Cool but not real cold days, low humidity oh yeah baby I feel a few more horses straining at the harness....

I looked at it a few days ago, after being parked outside for 12 hours in -19 deg C (-2 deg F) I would turn it on and it would idle at just under 1100rpm. after just under a minute it would drop to about 900rpm where it would sit for just over 2.5 minutes. from there it leveled off for about 2 minutes at 800rpm then it would drop to 5-600rpm, its low idle over the next 1 min. I know porsche says not to let it idle, but before my engine gets warm it seems to not perform nearly as nice (once it is warm it is awesome). I believe that in temps that are this cold the viscosity of the coolant and oil are high and not optimal, therefore wont circulate as well as they normally would at optimal temps. Also if I dont let it idle i wont hit the normal coolant temp (around 80deg) before i get to work which is an 8 minute drive away.

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With a commute that short, the best you can do is choose between two evils. I think in your situation, I'd probably let it warm up sometimes too, even though it's ordinarily a terrible idea. If your coolant is just warmed when you arrived, you can be sure the oil isn't.

You people actually know what kind of mileage you get? That's impressive. Mine is horrible, but that's self-inflicted, so I don't bother calculating. I just keep feeding it premium.

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This! Who cares, LOL

Who buys a Porsche and worries about fuel mileage?

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+1 I have no idea what mine gets. Drive time is Priceless.

I just burnt my first tank. 16.7 mpg. I could care less about what it gets, but I had reset it when I got it and was playing with buttons. lol

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Well, I have to admit that -2F is a bit colder temp at which I have ever started my Turbo. IIRC the coldest was one AM in Flagstaff where the temp was in the mid-teens. While I do not recall the engine acting odd, requiring a long idle time, etc, I do not recall now how long the engine idled or at what rpm it idled at so maybe your engine's behavior is normal. If so then to be sure gas mileage will surely suffer. The coolant's viscosity is really unaffected by its temperature unless the temp gets so low that the coolant's freezing temp threshold is crossed then the coolant is just slush at best. A real risk is destruction of the water pump impeller. Oil viscosity cold though plays a role. I would think running 0w-40 oil would be a necessity given the cold temps where you are.

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

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

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.

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.

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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.

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

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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.

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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.

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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!

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.

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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.

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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.

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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.

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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.

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.

I was wondering the same thing why a 500mph flying aircraft is being compared to an auto driving 60mph on the road? Some people sure over complicate things. Just like JR said, fuel blends up North. I dont think they change much down here because everything runs better from the cooler, more dense air.