Winter diesel
 

Hi all

Apologies if this has already been asked. I seem to be getting a sharp decrease in mpg during the winter months. I have heard that fuel retailers put an additive into diesel during cold periods to reduce the likelihood of it freezing??

Does anyone know if there is any truth to this and, if so, would it cause a decline in fuel economy?

Im not sure about the additive theory, but it's more probable that it's the colder weather and darker nights, engines take longer to warm up, lights are on earlier and also its more tempting to use the car for shorter trips during this period too. Also we use the air con more to demist steamy windows in the damp weather too. My last tank was my worse since buying the car with just under 60 MPG, im sure the weather is to blame!

Tire pressure will also drop with colder weather. So there are plenty of negatives that can affect the fuel mileage. A winter blend could be one of those negatives, but teasing out how negative from the rest would be difficult.

Look at it this way, better slightly worse fuel economy than getting stuck away from home from gelled fuel.

Yes tyre pressures, tyres will expand and contract more so check pressures, I checked mine on the weekend and they had dropped a fraction, only about 5% but over time, that would keep dropping.

Well actually the tyres will expand less - due to the lower temps (and likewise will therefore contract less too) , and unless you have a leak (very possible with alloy rims - in particular old ones (won't be your problem !)) the pressure will not keep dropping ... unless of course the temperature just keeps on dropping ..... in which case we all have bigger things to worry about ! :)

Well I meant the tyres will expand and contract more as the difference in daytime/nightime temperatures will be greater in the Winter, than in the summer months when the temperature only drops a few degrees during the night.

To provide an actual answer to this question, YES, there are different formulations of diesel fuel for the winter and summer just like gasoline/petrol. A quick google search will net you far more than you care to know.

Driving a diesel, I find it takes longer to warm up, and short trips just kill mileage. Solution, take the long way to your job/store/gym, or whatever. The few extra miles/minutes on each trip won't really cost that much, and you'll enjoy driving a warm car knowing your engine will appreciate it and will return better mileage to boot. Of course, being retired allows me to do this (maybe you can't) but you should warm up the oil at least weekly to avoid problems further on. Once warm, a few extra miles per trip doesn't really cost that much!
Tenderfoot

Yes a winter blend diesel will drop mpg. The tire pressure and longer engine warm up times also. I use a winter grill block on my 2011 Golf TDI. This gets the coolant up to temperature faster on a stone cold engine.

For sure, in Canada you get more colder days than we do in North Carolina, so a grill block would be very useful. Our temps seldom drop to single digits here so a block might cause overheating after a few miles, and would be beneficial only a few times a year. I see a drop of only a couple of mpg during our coldest months (Dec-Mar), so I just add a few extra miles to my short trips during those times. The car thanks me for it, and I usually have the time. The colder intake air rewards me with "crisper" engine performance from the denser air, so I get a good feeling by doing this. I'm not sure how long we get "winter blend" fuels this far south, so you might take a bigger hit up there in winter land. Our "hit" comes during our hot summer months where the A/C runs non-stop from May to October. We enjoy visiting your country, and your beautiful scenery. Have you been to NC? Golfing? Come on down, the weather's great!

Tenderfoot

Thanks for the invite Tenderfoot. Yes, I've been to NC a few times. Great place. Not much of a golfer but I do have some fanatical friends who are.

Does anyone see an increase in economy during winter? I was thinking as most cars are now turbocharged for power/economy reasons, does a turbocharger not benefit from cooler temperatures?

Turbos and superchargers will use an intercooler to lower the intake air temperature in order to counteract the heat generated by compressing the air. Cold ambient temps seem to help them as much as naturally aspirated engines. It may allow for faster warm up of the engine, but I've dropped 5mpg in the past couple of days, and don't think going into higher boost during the first part of my drive will help that.

If there is any benefit to cold air improving engine efficiency, it is small, and up against all the negatives of winter driving on fuel economy.

Thats what I thought. I guess perhaps long distance at a constant speed there may be a small benefit only.

Draigflag....question for you. Your car looks to be pretty aero, and you get great mileage. Do you drive it often, or do you have another daily driver? I can't believe you have recorded only 6 fill ups. What am I missing? I know England is a small country, but come on, you must have places to go and rack up some miles. What is your secret? Here in the USA, everywhere is miles away from where we live.
Just curious.
Tenderfoot

I think we all experience much lower mileage in the winter. My TDI will drop from the high 30s to under 20 mpg. shorter trips, higher friction, winter tire, winter blend, idle to warm up (a hopeless cause!) are all factors. Based on my understanding of diesels I would have though colder weather would help the diesels on long trips, but it does not. I have always seen best mileage is on warm days on the highway (up to 50 mpg) on the current TDI. it seems much more sensitive to temperature than the old (1999) TDI. Gas cars have similar experience, but I dont know if the swing is as large

Do diesels experience more DPF regen cycles in the cold?

Well I think the figure in my signature is UK MPG, works out about 52 US MPG, so it's not that great, but I do a lot of short trips during the week (this is my only car) which kills the MPG's. On the highway I get 74 MPG at 70 MPH, although in the government tests the car got 88 MPG. The best I had was over 95 MPG on a 30 mile low speed journey (all UK MPG's) Some hypermilers can get over 100 MPG in thier diesels over long distances, I have no idea how, but car manufactures are always coming up with neat engine map tuning to keep increasing economy. In Europe, there are strict C02 regulations, and as we know the easiest way to reduce C02 is to burn less fuel :)

Oh and I dont live in England, I live in an even smaller country! And everything is quite far from me too ;)

I use another factor when tracking fuel mileage; days between fill ups. I think this is a significant measure of trip length without any extra logging or record keeping. As an example, if you are filling daily, or a couple of days, then you probably have fewer stop and start cycles to sap fuel compared to longer fill up dates, and more starts. This is an obvious component to explain why highway mileage is more impressive than low speed, but short distance city driving, even though slower speeds (city) will show higher mpg consumption. I wish I could duplicate the 70-80mpg figures I see on the computer while driving on the city thru streets, of course the mileage when parked for days on end is very high and does not count.

I can't imagine having to fill up every few days, a tank lasts 3 to 6 weeks on my car depending where I go as I get 700 to 800 miles per tank. The manual says it's a 10 gallon tank, but I think with the reserve it holds a little more. That's why I like fuelly, regardless whether you do 1000 miles a week, or 10 miles a week, you can get a report at the end of the year with all your averages to give a true cost of running the car.

I prefer diesels too, as even though like any other car, short urban tips use more fuel, diesels are still pretty good on fuel. I think the least my car would do around town is low 50's MPG, still perfectly acceptable in my opinion.

Ok so I've been studying my MPG over winter. There's been a big drop, so I researched when the UK starts using winter diesel, and it pretty much explains my poor economy. We start using winter diesel on 16 November. I fuelled up exactly then, and my last few tanks have been below average. We stop using winter diesel on the 16 March, coincidentally I also filled up then (my current tank) and so far my economy on this tank is significantly better, Mid 60's MPG V's late 50's MPG on the winter blend.

So for anyone wondering, you can roughly assume there's about a 5% drop using winter blended fuel. Of course everyones circumstances and journies are different, but these are my results.