I am currently Benzless for the first time in nearly 5 years. As a result I am driving a lot more in my other vehicles, primarily a Chevy Avalanche with the 5.3 and a Subaru Outback with the 3.0.
Does the colder weather have a marked impact on fuel economy? It always did on my 240D but I blamed that on winter diesel and cold iron. Of course in around town driving where they never warm up the gassers will burn more fuel but I have made some long highway trips and it seems like even when warmed thoroughly they are using more fuel.
Is there winter fuel that could be contributing to this? Does the FI compensate (richly) for the colder inlet air and is this enough to make a notable difference?
I keep my vehicles in good tune, watch tire pressures and drive conservatively for the most part. I just drive quite a bit and want some insight (not the Honda hybrid kind ).
TIA

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

Yes, cold motor, cold oil, cold coolant. It all conspires to make the engine need more fuel. Diesel or gasser.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

No doubt about that Tom but I'm concerned with the economy after already warming up. Just trying to decide if I have a problem. Highway economy has dropped 10-15% with the cold weather-and this is with several hundred mile trips where nothing is still cold (except the incoming air).

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

Not sure about Oklahoma but here in Chicago the winter blend gas always kills my mileage.

Continuing Toms explanation, how FAR are these highway trips. It takes awhile for drivetrain to warm up enough to reduce the losses Tom described. The only thing I would add is that cold starts and warm ups require richer conditions until normal operating temp is reached.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

Its hard to say if it could reach 15%. How many tanks have you measured? All are only highway miles? ...200 mile trips? did you check your tire pressure?

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Everything is in order with the vehicle. I check tire pressure fanatically, the plugs, wires, all filters, all fluids, belts, fan clutch, knock sensors (with intake gasket change) and battery are new in the last couple months. We're talking about 2 400 mile trips (nonstop), a couple of 100 mile trips and a couple of 50 mile trips plus normal driving around. Average 2000 miles per month.
Yeah, not sure about winter blend fuels here. I imagine that a combination of winter fuel and low air inlet temps (causing the engine mgmt system to run richer) are my problem. I'll just drive on and assume there's nothing amiss, especially since I don't know what in the world I'd change. Like I mentioned earlier this is the first winter I've driven extensively NOT in a 240D since 2007-2008. It just seems like my economy has fallen off in the last month and I'm looking for explanations.

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

FWIW - I noticed drops in MPGs on my cars when my local station switched from summer blended fuels to winter blended fuels.

__________________
-Justin

91 560 SEC AMG - other dogs dd
01 Honda S2000 - dogs dd
07 MB ML320 CDI - dd
16 Lexus IS250 - wifes dd

it's automatic.

iwrock, that's probably all it is. I'm just frustrated because I've done all this work to bring the vehicle(s) up to top condition and the economy falls off.
On another note iwrock, my son is about to transfer to Beale AFB in Yuba City. How near is that to you?

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

The operative words here are "seems like".

The problem with the conclusion is the fact that you really cannot measure the consumption when the engine is fully warmed. You would need to bring it to a station and fill it..........and never shut it down before refilling it...........and then calculating the fuel economy.

Anytime is sits for more than 1 hour, it must rewarm itself.

If it is fully warm, the fuel consumption in colder air is the same as the fuel consumption in warmer air. The computer management systems must provide the perfect fuel air ratio independent of air temperature.

However, the available horsepower and the ability to use additional fuel is greater in colder air due to the increased density.

Most every time I kept track of winter mileage per gallon, it was usually lower. Gasser or diesel powered.

My truck always loses a bit when they switch over to winter fuel, my average goes down from 15-16 around town to 13-14.

I know when they do it to, the tank to tank difference is dramatic. This year I got a swig of winter fuel as soon as I filled my truck up after I got back from vacation.

__________________
1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

My experience has been that all cars use more fuel in winter. At least a 1-2 mpg drop. Colder air over the radiator means more heat loss. Heat that came from burning fuel. Most of the fuel burned is wasted anyway in a gas or diesel engine. Heat loss to cooling system, heat loss out the tail pipe, heat loss in friction.

Well, it looks like a consensus. The drop was sudden and about 1.5-2.5 mpg. Looks like a combination of cold wx and winter fuel is sapping my mileage. I'll just drive and not obsess.
Thanks!

__________________
1983 M-B 240D-Gone too.
1976 M-B 300D-Departed.

"Good" is the worst enemy of "Great".

It is less than 10 miles from my house, just over the county line. Still some snow on the ground right here that wrecked my garden.

__________________
1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)