Alright Mike, not trying to prove you wrong but I want to figure this out.You say cold IAT drop MPG big time on yours.You say Winter Fuel drops it.So why is it that running winter fuel with no winter front whatsoever at 25F ambient at 70mph, do I get the same 21mpg (actually 21.54mpg) that I get on a 100F day? I get consistent mileage all year, summer or winter fuel, rain snow sleet or hail. I know everyone here seems to have this "it's winter fuel, so it's ok to see 2mpg loss" but why am I not seeing this loss! I am thinking if I could figure this out, I could help you all not get a loss either.

Like on my truck the more I watch the IAT temps the colder the tem pgets to about 60*F then it seem to stop. Like right now my best MPG for going to the store and a fire meeting is like 14-15 MPG... Driving easy because of snow and icy roads 40-55 MPH tops. Then the added load of using my 265/75 R16 Cooper STTs which are a extra 20 pounds per tire. Then cold air is denser so more drag on the vehicle. It just goes on and on... Let me get the vid camera out and do a short run with you guys...

Then cold air is denser so more drag on the vehicle. It just goes on and on...

And what I am saying is the "on and on" seems to just be an excuse.. Why am I not seeing it? I was going into a 20mph headwind on the way there at 75-80mph and still got 19.5mpg, which is what I get on a calm 100F day in the summer going the same speed. On the way back at 70mph, on level ground my EGT was 490F since I had no winter front. All of this equals degraded mileage, but I got the same 21.5 that I get in the summer, why is what I want to know. I always thought my odometer was wrong but I checked it for once with the road signs saying sedalia 74 miles or whatever it was and 74 miles later I was 4 miles into sedalia, so the odometer is dead on if not a few miles short of what I have actually gone.

Here you go... A quick video of going towards New Meadows, ID where its colder... Brrrr... Now if I drove all the way to to McCall, ID 35 miles and went shopping like typical and drove the same way 45-55 MPH the whole way I might tip the MPG at 15-16 MPG's for the trip... But now same thing in the summer time and 80-90*F weather I can pull nearly 21-22 MPG's... The only thing different between the two trip would be the tires (235/85 R16) and the winter front.

Depending upon the area and cold weather climate extremes your area typically encounters, diesel fuel is blended accordingly to prevent gelling, wax crystals, etc. This is normally accomplished with varying blends of #1 and #2 diesel as well a various additives which help lower the gel point or wax point of diesel fuel. #1 diesel has less BTU's than #2 diesel. More #1 diesel must be burned to achieve the same amount of work. Another issue that comes into play is that a diesel engine must develop enough heat in the cylinder and surrounding area to develop efficient combustion. In cold weather conditions, more diesel must be burned to achieve and maintain this level of heat. Here is a good primer on diesel fuel: http://www.chevron.com/products/tips/fuel-school/?&aID=54&cID=15

Mike, are you just going by that thing or are you hand calculating the tanks also? Liveoak, you are right and all of this is well known fact, which is why I am trying to understand why mine never notices it. I don't know what tests I need to do to find out what makes mine run the same regardless.

Mike, are you just going by that thing or are you hand calculating the tanks also? Liveoak, you are right and all of this is well known fact, which is why I am trying to understand why mine never notices it. I don't know what tests I need to do to find out what makes mine run the same regardless.

Both... I've got my Excel sheet, notebook, and then the good ol' ScanGauge II...

ISX, the 1st gens also have a higher compression ratio than the 2nd&3rd gens do. So more heat is produced when the air is compressed which helps combustion/mileage. 1st gens are all mechanical too...........no sensors to instruct the engine how much fuel to inject based on the input from them. Cool/cold air is dense air........the sensors will adjust the amount of fuel injected based on that to maintain pollution standards. IAT, TPS, MAP etc..............the 2nd and 3rd gen trucks because of these the fueling map in the programming continually is monitored and changes based on the inputs.

ISX, the 1st gens also have a higher compression ratio than the 2nd&3rd gens do. So more heat is produced when the air is compressed which helps combustion/mileage. 1st gens are all mechanical too...........no sensors to instruct the engine how much fuel to inject based on the input from them. Cool/cold air is dense air........the sensors will adjust the amount of fuel injected based on that to maintain pollution standards. IAT, TPS, MAP etc..............the 2nd and 3rd gen trucks because of these the fueling map in the programming continually is monitored and changes based on the inputs.

That might all be true, but I wouldn't think it will drop the mileage to the point of what Mike see's, thats like 8mpg less than what he gets in the summer. I don't see how sensors would screw it so badly to cause 8 mpg loss, its mindboggling. If it took that much fuel to get the same power then it should be pouring black/white smoke the whole time because it would be running so inefficiently. I just don't get where it is using it all.

That's the thing by the time I cover about 20 miles then it levels out ot about 16-17 MPG... But that first fire up of the morning cold is my killer... Trust me I know why all the diesel leave there trucks idling. It cheap to leave it idle than starting cold and wasting fuel to warm it back up. At least for the computer controlled trucks. Also remember there is very little flat ground here in Idaho so either way I travel I'm either going up a slight grade or down a slight grade. Going south like I did I'm on a slight grade for 20 miles going from 2,800 to 3,500 in 20 miles... Or going south 20 miles and drop from 2,800 to 1,800 feet. Every road out here follows a creek, stream, or a river so it goes up or down regardless... Now even in the summer time I hit much better number going that direction I'm typically doing about 16-18 MPG by the time I'm in New Meadows proper I'm still hitting 22 MPG. I done another run last year from Home to Cambridge ID driving 55 MPH. When I got to Cambridge ID I'd barely pulled 15.9 MPG but the morning temps where like 25*F and IAT was 65-70*F the whole way. Then by the end of the day the temp had rose outsie and weather warmed considerable amount 65*F outside and I was able to hit my IAT mark of 95-100*F and BAM! Instant jump... I was back to 20-21 MPG... But remember also I've got changes to the vehicle too. Winter fuel, larger and heavier tires, colder temps, etc. So the loss is my typical...

That's the thing by the time I cover about 20 miles then it levels out ot about 16-17 MPG... But that first fire up of the morning cold is my killer... Trust me I know why all the diesel leave there trucks idling. It cheap to leave it idle than starting cold and wasting fuel to warm it back up. At least for the computer controlled trucks. Also remember there is very little flat ground here in Idaho so either way I travel I'm either going up a slight grade or down a slight grade. Going south like I did I'm on a slight grade for 20 miles going from 2,800 to 3,500 in 20 miles... Or going south 20 miles and drop from 2,800 to 1,800 feet. Every road out here follows a creek, stream, or a river so it goes up or down regardless... Now even in the summer time I hit much better number going that direction I'm typically doing about 16-18 MPG by the time I'm in New Meadows proper I'm still hitting 22 MPG. I done another run last year from Home to Cambridge ID driving 55 MPH. When I got to Cambridge ID I'd barely pulled 15.9 MPG but the morning temps where like 25*F and IAT was 65-70*F the whole way. Then by the end of the day the temp had rose outsie and weather warmed considerable amount 65*F outside and I was able to hit my IAT mark of 95-100*F and BAM! Instant jump... I was back to 20-21 MPG... But remember also I've got changes to the vehicle too. Winter fuel, larger and heavier tires, colder temps, etc. So the loss is my typical...

I wonder what would happen if you put a 100F fooler on that IAT... This instant bam thing has me wondering. Obviously mine runs all year on the same settings so it's not like you fooling it into 100F would be any different, I just wonder what effect it would have.

Let me play with the idea... I'm sure there will be a impact of some sort...

Let me play with the idea... I'm sure there will be a impact of some sort...

An impact of making your mileage go back up... I never see an impact from 0-100F, always runs the same always gets the same mileage, all on the same timing. I really want to see the results of this

Just for a baseline number I pulled 16.5 MPG from Home to McCall, ID and back to Home 74 mile trip to go grocery shopping. Weather today was 43*F and thw IAT temp was 83-85*F most of the trip. So as you can see just the few degree rise from the video has gain back a bit of it... Tomorrow I'm going to play with my resistor collection and get a temp close to 100*F IAT and do another run at 120*F and see if there is a difference...