Mileage and temperature

Trupiano · Apr 12, 2013

I know the principles of an engine, performance, mileage and everything.

But I find it funny that whenever it's 40 degrees out, my mileage is tanked but I have tons of power.

And when it's 70-80 degrees out, my mileage is great, and maybe a slight change in power decrease, but nothing really noticeable.

When it was 70, my lies-per-gallon over head display read 17.3 avg... which in turns ends up around 16.5 mpg hand calculated.

And when the temperature drops, my avg drops to around 16.3 lies-per-gallon, whis is about 15.5 hand calculated.

There's no change in my driving habbits, if anything I try to coast more when it's cold to try and save a few more mpg's.

But alas, it doesn't work. Does this have to do with the intake air temp and how the engine/computer react to add more fuel, or is my truck just warm blooded?

Ocelot · Apr 12, 2013

Mine drops quite a bit in cold weather. In fact any of my trucks in the last 15 years or so all dropped mileage in cold weather.

Part of it is winter gas, but most for me has been temp. Even with the same gas, my mileage went up significantly last weekend and early in the week when we had a warm spell and it got into the 70's

Ray

Etroze86 · Apr 12, 2013

Milage does take a dive here specially when it hits -15F at that time i was getting like 10MPG now that is around 25F I get 13-14 MPG.

Cthulhu · Apr 12, 2013

Really if you think about it, your mileage theoretically should get better in the winter.. That's the idea behind a CAI anyways.

You take in more dense, cold air. The air then is heated to a specific X at operating temperature which should release more energy because it is more dense.

Now, I've noticed the same thing with my diesel. I have no doubt its due to the winter-fuel as I lived up north and could start the truck at -40C without worrying about the diesel gelling.. so there's definitively an additive in there preventing that. I remember as a kid at -20C my father's truck had to be brought into a shop to get the diesel to de-gel. Like the OP said though, they don't change it based on how warm it is outside... it shouldn't make a difference one day to the next. I'm wondering how much validity there is to a CAI theory, or if for some reason warmer air into the engine is actually a better idea.

Chewy · Apr 12, 2013

For every 11º F up or down your power will increase 1% up or down. Colder = more power while warmer = less.

My car goes from around 23mpg in the summer to 19 in the winter all calculated with my fuel app and not the DIC.

audio1der · Apr 12, 2013

I can't wait for warmer weather to get our damned mielage back up. 17.5L/100km driving an empty truck without a heavy right foot hurts.

As for winter gas, do you gas use stuff which advertises additives? I avoid that $hit like the plague. When I'm paying this much for fuel, give me 100% fuel and let me decide if I want antifreeze added to it.

I think its the volume of the dense, cold air and the vehicles dumping more fuel in to mix with it.

Cthulhu · Apr 12, 2013

Audio1der, you might have a point there.. with dense cold air, without adding more fuel, you would have a lean condition... which of course would cause the engine to add more fuel.. Really cold air, add more fuel.. warm air, less dense, so when it gets measured, it needs less fuel.

Hmmm.

BlackedOutHemi · Apr 12, 2013

Cthulhu said:
Really if you think about it, your mileage theoretically should get better in the winter.. That's the idea behind a CAI anyways.

You take in more dense, cold air. The air then is heated to a specific X at operating temperature which should release more energy because it is more dense.

Now, I've noticed the same thing with my diesel. I have no doubt its due to the winter-fuel as I lived up north and could start the truck at -40C without worrying about the diesel gelling.. so there's definitively an additive in there preventing that. I remember as a kid at -20C my father's truck had to be brought into a shop to get the diesel to de-gel. Like the OP said though, they don't change it based on how warm it is outside... it shouldn't make a difference one day to the next. I'm wondering how much validity there is to a CAI theory, or if for some reason warmer air into the engine is actually a better idea.

audio1der said:
I can't wait for warmer weather to get our damned mielage back up. 17.5L/100km driving an empty truck without a heavy right foot hurts.

As for winter gas, do you gas use stuff which advertises additives? I avoid that $hit like the plague. When I'm paying this much for fuel, give me 100% fuel and let me decide if I want antifreeze added to it.

I think its the volume of the dense, cold air and the vehicles dumping more fuel in to mix with it.

Yep! A true CAI does not make better gas mileage, it actually drops it. The colder air drawn in is denser, therefore more fuel and therefore, worse mpgs but better power. These HEMIs get ballsy when it gets below 40 outside. Haha. I love it.

jlb · Apr 12, 2013

Cthulhu said:
Audio1der, you might have a point there.. with dense cold air, without adding more fuel, you would have a lean condition... which of course would cause the engine to add more fuel.. Really cold air, add more fuel.. warm air, less dense, so when it gets measured, it needs less fuel.

Hmmm.

I kind of thought about that, and almost posted, but wouldn't the butterfly valve in the throttle body limit the amount of air to the right amount for your throttle position based on ambient air temp, and the mass air flow sensor? Then you wouldn't be lean...

I am not sure on this whole issue just voicing some thoughts lol

Cthulhu · Apr 12, 2013

JLB - You might be right.. but the TB would measure the volume of the air, regardless of the density. At the TB, the air would be close to ambient temperature, hence as it moved into the engine it would warm up and expand. If the sensor is near the outer perimeter of the system, it would not be able to adjust in time.. however the fuel mixture in the engine would be adjusted by the knock sensors which I believe are near the head IIRC. If someone knows different, please let me know as I am a computer tech... just trying to reason my way through this discussion.

Chewy · Apr 12, 2013

Your IATS will also tell the engine what the temp of the incoming air is.

Ocelot · Apr 12, 2013

We don't have a choice on the winter gas here. All I know is my mileage jumps up in the spring when we start getting warm weeks. Once the temp gets down even to the 30's or 40's it drops a lot.

I do waste gas though warming it up with the remote start when its below freezing.

kkreit01 · Apr 12, 2013

I noticed the same. The last tank I finally broke 14 in town. It was fairly warm (60s/70s). Now it's back down to 30/40s, and I'm less than 13 so far with this tank.

Chewy · Apr 12, 2013

My MPG drops for a few reasons in the winter. #1 winter fuel, #2 Snow tires, #3 my DOD (MDS) doesn't activate under somewhere around 35º F or so. 4 mpg is a lot to lose.

Hornet · Apr 12, 2013

Specific Gravity of fuel changes when it's cold too.
Between the putor compensating for more condensed air molecules in the intake charge the fuel also becomes heavier when it's cold,and will phsycally flow more fuel volume through the same size opening.
Look at your plastic jerry cans .if you fill them at 70F,and cool them to 10F,the sides will suck inwards,as the fuel condenses and subsquently becomes heavier for the same volume of space .

Trupiano · Apr 12, 2013

Thanks guys, glad I'm not the only one! Makes sence with what you all are saying.

Hornet · Apr 13, 2013

Throw in the fact that everything is harder to turn when it's cold is also a big contributor.
Oils are thicker and create more drag,seals are stiffer and generate more friction etc.,(especially your outer axle seals,the ones that don't see much heat on a cool day).
Tires are stiffer and harder to rotate,they also lose air pressure in cooler weather

And one factor you don't see mentioned often is the actual air friction generated by the truck.
Colder air is denser/heavier,and it takes more horsepower to push the same frontal area through the air at 40F then it does at 70F.

Horsepower is a by product of btu's produced,and the only way to produce more btu's in a given set-up is burn more fuel,to consequently get the horsepower needed to push the truck through the colder /denser air.

There's a pile of factors that contribute to mile-age changes in relation to temperature changes

audio1der · Apr 13, 2013

This is a fascinating thread!

Hornet · Apr 13, 2013

Where abouts are you located in Airdrie?

jlb · Apr 13, 2013

Definitely one of the better threads that have been on here in a while lol, no sarcastic arguments yet... I love it

I like the air resistance theory, that one makes a lot of sense, but for the city mileage part I don't think it would make much difference due to low speeds. The oil part makes a lot of sense as well, especially rear diff oils since they don't build heat unless the truck is moving unlike the tranny, and engine.

The specific gravity of fuel one is very interesting because it actually varies by about 8% which could mean your truck depending on which specific gravity constant they use could get a lot worse fuel mileage, and run really rich in the winter. I would think that would be a better way to tune than really lean in the summer.

Mileage and temperature

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