Hi,

Does anyone know why these trucks get much worse MPG in cold ambient temps?

I have an 01 4runner, V6 4X4, pretty much standard, slight lift(99springs), 16"wheels w/slightly larger tires than std, it's well maintained. This winter I was averaging 15.5 mpg in city driving, now that the temps are 50-60 I am getting 18-18.5 yesterday. There is a similar difference in highway mileage.

Is it the 4x4 gear being cold and putting a drag on things or maybe the ECU does not handle the cold temps well. I don't warm it up all that long, it's garaged, minute or two and then drive it slow until the temp gets up.

It's been this way since new, what is it?

Thanks
Doug

 

It takes longer for it to reach closed loop. The fluids and lubricants are thicker causing more friction, having to let the vehicle warm up (even for a few minutes). Tire pressure is down due to the cold.... I'm sure theres more reasons...

 

I actually see a tad better mpg when it's cold. I'm guessing the more condense the air is, the more you can squeeze into the cylinder.

 

There is also slightly different gas formulas in the winter in colder regions. The "winter mix" usually gets slightly less mileage.

 

Two factors. One is what dirtyX mentioned. Winter gas formula has at least 10% ethanol mixed in it. It burns cleaner, but your MPG suffers. They put that in so that smog is reduced.

Secondly, the air is colder, which means denser. This traslates to richer fuel mixtures, which means less MPG (but slightly more power, though). Both of those attribute to the lower MPG you noticed. We all go through it.

The "drag" from your diffs really isn't the cause. I don't think anyone's noticed any MPG gains after switching to synthetic.

 

I did...

 

Alot of gas stations use 10% ethanol all year round but with my truck it seems to be more affected by air temp than "winter" gas since when Denver was getting near 70s through Jan and Feb my mileage would rise 1-2mpg during those warm weeks vs the weeks of under 30F and colder.

I know I also may have an issue with my TPS but most of us should see an increase in MPGs in warmer ambient temps and that is normal.

 

I'm thinking that Crackalak is on the right track, with the denser air. I know that the higher an aircraft with a reciprocating engine goes, the more you need to lean out the mixture. I thought that the MAF would take care of that in our trucks, I guess it only measures total airflow and not how dense it is or the temp. We can then expect real good mileage on a hot/humid day, maybe it's time to start taking density altitude measurements and keep track. The ECU must know the ambient temp so it can adjust idle and mixture, what sensor gives it that info?

I check tire preasures often and have adjusted my mileage for the slightly larger tires.

Thanks
Doug

 

The MAF or IAC will tell the ecu what temp the air in the intake is

Cold engines run richer, part of the reason is they will start and stay running easier that way. It takes longer to reach operating temp.

That is the biggest reason IMO

 

Really? You changed out your diff fluids to syn and noticed MPG gains?