can someone explain how cold weather kills MPG?

this is crazy to me! all conditions were the same, i make the same drive every day for work! one day it was 20s and 30s and i got 14.5 mpg. A few days later it’s in the 50s and 60s and i’m back to getting 17mpg on the commute


am i missing something or is this normal and i’ve never noticed it before?

 

From fueleconomy.gov

 

Big drop in tire pressures.

 

How long do you sit idled in the coffee line when its cold?

 

Cold air is denser than warm air. More air molecules are being sucked in by the engine for the same volume of air, so maybe more gasoline is needed to burn optimally.

That's what I would guess, but math and science are not my strong suit.

EDIT: I forgot that everything has electronic throttle bodies these days. Do electronic throttle bodies adjust at all based on temperature, I wonder? If so, this might be more of an issue for cable-controlled throttle body vehicles.

 

^^This for sure I know as fact^^

 

This is the only answer.

 

Everything being correct and equal from the list posted above (i.e. tire pressures are correct, your vehicle is at operating temperature, etc) then the biggest factor is the gasoline. Cold air is more dense so you get more air in to the engine, so that helps offset any additional drag that extra density is causing. The thing about making your alternator work harder because of the electronics, I don't buy. The alternator puts so little drag on the system that I doubt it makes any difference. On the flip side, your AC compressor in the summer puts way more drag on the system than the alternator. So the biggest difference is the fuel, winter blends vs. summer blends.

 

Alternators make a huge difference, the recharge of the battery after cold start is a huge draw. Also just using more current with heaters uses fuel.

Have you ever used a battery charger on 60 amps? The lights dim when you turn that sucker on.

 

The .gov post above mentions it, but winter gas is usually less efficient than summer gas.

 

I'm not riding my bike in the cold weather

 

It's not the draw that makes a difference. It's the amount of resistance the alternator put on the engine that makes it have an impact and if you've ever spun an alternator by hand and generated power, you would know there's almost no resistance. No go spin an AC compressor that has the clutch engaged pumping freon through the system and you'll quickly see how big of a difference it is.

 

In TX, essentially the same impact as western WA: Winter fuel is #1 killer.


"Winter grades of gasoline can have slightly less energy per gallon than summer blends."

I absolutely now know this as fact.

Given: Refinery blenders say winter fuel is being delivered. Step A.
Step B: Temperature is the same or actually goes UP.

MPG drops............across multiple vehicles.

That is NOT some weather induced MPG loss. Period.

PS there are multiple exact threads on this.

 

https://www.tacomaworld.com/threads/gas-mileage-vs-weather-changes.637603/

https://www.tacomaworld.com/threads/260-miles-on-a-full-tank.638414/

 

They can use from 3-4 hp, not as much as an ac compressor, but thats a lot when you consider how little power is made under 2000 rpm.

Modern cars have current sensors to help reduce load from the alternator simply for fuel economy.

Saying alternators don't cause fuel loss is like saying 285's don't rub.

 

Too cold in New England winters for this, plus I'd rather not ruin it..

 

thanks for all the good info guys, i was thinking tire pressure at first too but then i raised them to what they were when it was warmer and still low mpg... also i don’t let my truck idle or warm up, i get in a go. but sounds like fuel may be a key factor here which i had no idea

 

Does anyone here have URD's O2 sensor simulator? I know the computer runs a rich tune to get the cats up to temp but if it thinks they are already running optimal will it lean out?

 

I can get 91 octane non ethanol fuel all year round, I maintain my tire pressure. I commute 50 miles a day, don't warm up my truck. It makes no difference. I chalk it up to the dense air as stated above. It does seem more drastic with this vehicle than any other I've had, and I've had many.