As i was warming the car up then i noticed my ave mpg dropping quick like -0.1 for every 10 secs. I warm up my car about 1 minute before i drive. The weather outside was in the low 40's.

 

The car not being a peak operating temperature negatively impacts fuel economy.

 

I think I am doing pretty good in this cold weather.

I usually do 80 to 90 on my drive to work in the morning, and my tank averages about 24.5.

Winter is nice. :P

 

it does in my truck, 13 avg when warmer out....10 if i am lucky when its cold

 

Mine went down to like 16/17 but when i drive it goes up.

 

that thing looks like it chugs like a frat boy. gas that is.

 

My RV gets better mpg then that. Time to sell that dog

 

I've noticed 14-16 mpg average when the engine is cold..once it warms up I can get up to 23 mpg city driving.

 

Not considering the warm up factor, in general cold air is more dense that hot air, and therefore has more oxygen per unit of volume. This will increase gas mileage as the computer adjusts the timing accordingly.

 

Check your tire pressure, I've been getting low pressure readings in the morning when it's below freezing. Pumped those babies up today and I'm riding smoother and seems to be getting better fuel economy.

 

Wouldn't the computer adjust the timing by adding more fuel to the mixture causing a reduction in gas mileage?

 

Thole saw my avg mpg, I was getting 16 when I started the car..i drove it a little then it jumped back to 19-20

 

Novais350 are getting 16/17 b4 it was even cold. lol

 

Heavy right leg and foot man...I got it in the summer of 62 in NAM..sike!!

 

It won't change timing at all. It will change injector duration, but ignition timing will remain where it should be once the coolant in the engine's water jacket stabilises at 82 C.

The ECM will add the correct amount of fuel for the amount of air entering the engine as measured by the MAF and corrected by feedback from the WB O2 sensors on each side of the engine. It will not change ignition timing. That's not how it works. Timing is based on combustion chamber design and engine operating temperature, not air temperature (unless the engine is air cooled, then you're screwed for fuel AND timing because the engine's operating temperature is unstable.)

Water cooled engines maintain a relatively stable cylinder head temperature - once they are at operating temperature. The problem in cold weather is it takes longer to heat soak the head, cylinders, pistons, and cooling system. The energy used to get these items up to temperature is NOT used to rotate the crank, so it is completely lost.

This gets at one of the fundamentals of engine operation - every heat cycle is followed by a cooling cycle, and everytime the ignition fires, some of the heat of the reaction is lost to reheating the engine's components and cooling system. The ideal engine would have its components completely thermally neutral - not adding or subtracting any heat from the chemical reaction, but those materials don't exist today.

That heat is both lost efficiency AND lost power. If the heat is absorbed by the cooling system and carted off to the radiator, then it surely didn't push on the piston and give us kinetic energy to move the car. The colder the starting temperature, the more energy will be lost this way.

The other issue with outside air temperature is it doens't vaporise fuel very well when it gets colder. Yes, I am keenly aware that fuel injectors spray fuel into tiny droplets. I'm also keenly aware that those droplets will combine if the intake air is cold, and bigger droplets do not burn as efficiently as smaller ones do. With the GDI in the ISx50s we get a BIG plus for efficiency because the fuel gets injected directly into a very warm cylinder instead of being splashed on the backside of an intake valve in hopes of gaining some heat to assist vaporisation. Still, the colder the intake air, the more fuel gets "wasted" heating the air from its initial temperature.

If you look at the super efficiency engines, you see the engineers very carefully control intake air temperature to acheive low brake specific fuel consumption. And they like the air to be as warm as it can be without promoting detonation. Ideally, you need control over air AND fuel temperatures to get maximum efficiency (and if you think about it for a minute, you need precise control of the same things for maximum power.)