DFWDieselJet
Veteran Member
Ok, question for you gurus...
In my brief esperience with my TDI, I have observed something which seems to counter popular wisdom here on this board.
The conventional wisdom is "warmer air equals better mileage."
I've observed the opposite...as the temps have fallen (from a high of about 95F to 35F), my MPGs have climbed from the low 40s to around 50, under otherwise identical driving conditions (highway, 73-75mph).
And there is one big "problem" in my mind with the warmer air=better MPG idea. Why do we have intercoolers? TDI's never generate enough boost for the temp to REALLY get up there, and detonation is not a problem as in gas engines, and gas engines of similar boost levels have been sold without intercoolers...so why do we have them? Germans are pretty good engineers, and accountants too...they wouldn't needlessly put an intercooler in these cars if it did not have a positive effect on HP or MPG.
And if warmer air helped MPG, why isn't bypassing the intercooler a common hypermiler-mod? In fact, it's the opposite...keeping it clean and efficient is routine maintenance for the economy-minded.
Sure sure, there is the air density argument...but I'm really having a hard time wrapping my head around the idea that it's a significant difference. And at city-driving speeds, where wind resistance isn't a huge factor, any difference would be futher marginalized.
And as for the colder temps = less rolling resistance, intuitively, I think that would be the exact opposite since colder temps=harder tires and road surface, and harder tires usually means better MPG.
Ok, so fuel is reformulated in colder temps for gelling reasons, but that's not directly a temperature effect...it's indirect. I suspect this is the main..if not ONLY...culprit here.
<flame suit ON>
In my brief esperience with my TDI, I have observed something which seems to counter popular wisdom here on this board.
The conventional wisdom is "warmer air equals better mileage."
I've observed the opposite...as the temps have fallen (from a high of about 95F to 35F), my MPGs have climbed from the low 40s to around 50, under otherwise identical driving conditions (highway, 73-75mph).
And there is one big "problem" in my mind with the warmer air=better MPG idea. Why do we have intercoolers? TDI's never generate enough boost for the temp to REALLY get up there, and detonation is not a problem as in gas engines, and gas engines of similar boost levels have been sold without intercoolers...so why do we have them? Germans are pretty good engineers, and accountants too...they wouldn't needlessly put an intercooler in these cars if it did not have a positive effect on HP or MPG.
And if warmer air helped MPG, why isn't bypassing the intercooler a common hypermiler-mod? In fact, it's the opposite...keeping it clean and efficient is routine maintenance for the economy-minded.
Sure sure, there is the air density argument...but I'm really having a hard time wrapping my head around the idea that it's a significant difference. And at city-driving speeds, where wind resistance isn't a huge factor, any difference would be futher marginalized.
And as for the colder temps = less rolling resistance, intuitively, I think that would be the exact opposite since colder temps=harder tires and road surface, and harder tires usually means better MPG.
Ok, so fuel is reformulated in colder temps for gelling reasons, but that's not directly a temperature effect...it's indirect. I suspect this is the main..if not ONLY...culprit here.
<flame suit ON>