Crisp fall is here and I'd thought that without defrosters, air conditioning, and watery roads I'd see improved mpg. I even thought that the cold air would expand more when heated in the engine and give a little extra mpg. Far from it. After making nearly 50 mpg on each tank, I barely made 48 on the last tank and this tank is a struggle to get above 44 mpg. I understand that the engine starts cold and that for emissions the first priority is to warm it up; the engine does not turn off at stops until it has some heat. Nevertheless, my average commute is 45 miles so there is plenty of time to warm up and then settle into good peformance. No such luck.

Any insights (besides checking my tire pressure which I'll do tonight)?

 

all that you mentioned, plus winter-blend fuel has lower energy content than summer-blend.

I made the error previously of thinking the difference was in the oxygen content, which it is not. Thus I thought the mpg difference was in our heads or due to other factors. I was wrong.

Winter fuel is literally 'lighter' and evaporates more easily- for easier cold starting and because in summer temps there is more evaporation, so they reduce the volatility in summer fuel to counteract that.

Lighter molecules mean fewer atoms --> fewer chemical bonds from which to get energy --> lower mpg.

 

Tell me about it. Current temps and my appauling non-LRR new tyres have hit me -10 mpg compared to mid summer...and it's likely to get worse.

If you can, try to rig up a warm air mod or radiator block - that's what I was going to do until I realised that the 'sardine tin' like situation in my engine compartment leaves me no room to do anything!

 

i have yet to put on the winter tires, but we have been below freezing the last week or so at night. i have two miles of gravel road to drive as the car warms up, so i guess i must use up all the lousy mileage there. once i am on the highway, i am still showing around 54, but i admit i do have to work harder to get there.

just for kicks, i compared the gas usage on this car, which i just bought, to the honda crv i just bought about this time last year. i have about 4600 miles on the HCH and have used about 85 gallons of gas. with approximately the same mileage on the CRV last year, i had already used 182 gallons!!! what a difference!

 

hmm...winter to me means higher MPG . No AC use anymore. But then again, winter also means Mid-Jan through Early March

 

As a tip that goes with the radiator block, keep the cabin heat off until the engine is warmed up.
Remember that when the temp gauge first reachs normal (1/2) it's the coolant that has reached operational temperature, not the complete engine, or drive train, bearings, etc.

I have a similar distance commute as drquine and for my first 12 miles the cabin heat is off and the **** set to cold, and at 12-22 miles (~15 minutes) it is switched to full hot but the fan is still off which allows a passive air flow over the heater core.
At the 22-25 mile mark the drivetrain is fully heated (Worked loose) so the fan is set to what ever.

I realize this may not be practical in everybodys case, but it's only a tip where it is applicable.

That way the tiny amount of gas only has to work and heat the engine, not the engine & cabin.

 

May this would be a good time to switch over to the 89 octane with lower volatility.......???any thoughts??

 

Folks with garages would probably fare much better, heated garages even better but unfortunately my HCH will have to brave the great white north unprotected for the winter....even if the garage is 45F while outside is 32 or less may be beneficial...we just had 2" of snow and 32F here last saturday and it killed my mpg's, slowly getting back up to 47mpg. Sunday, the next day, it was 70F...yeesh new england weather....

 

Not sure if that would help, but worth a try. The higher octane is achieved through additives, though not necessarily ones that add much energy content. There are other differences in winter/summer blends across octane levels, too. I presented a simplistic view of volatility before.

Think about E85...105 octane and lower volatility but worse mpg.

 

wow. snow. i was wearing a tank top today. ha!