You get more power with a denser charge; air is denser as the temperature drops; so is gasoline, but the changes in density with temperature are not the same for both.

Although the ideal A/F ratio is often cited as 14.7:1, your engine is rarely at that exact ratio (because you generally can't burn 100% of the gas and air; combustion is less efficient than that, and efficiency also varies with temperature).

Power is increased at a slightly lower ratio, economy is increased at a slightly higher ratio. Best power is typically closer to 13:1 and sometimes slightly lower; best economy is typically at or above 15:1.

Assuming an engine at operating temperature, during acceleration at part throttle you will have more fuel (lower ratio), during Wide Open Throttle (WOT) you will have the most fuel (lowest ratio in the fuel map of the computer) and at cruise the ratio will probably be leaned out as much as possible (highest ratio).

Since the air and fuel mixture is denser and WOT is pretty much "all the gas you can get" which results in "all the power your engine is capable of" fuel consumption is higher with a cold charge when you use your right foot aggressively.

The effect will be less if you drive with a light throttle, and if you are working the engine hard (towing, etc) MPG might actually improve.

Most gas pumps correct the density of the gas you buy to what amounts to room temperature. What that means is the gallon of gas you buy is only actually one gallon in volume at that baseline temp (I think it's 18C/68F around here, but can't remember for sure ... there's a sticker on the pump that says what it is, though).

If it's 32F outside, you pump less than a gallon while paying for one. If it's 100F, you get slightly more than a gallon in the tank. If you can buy gas at a station that doesn't correct volume, you will pump a bit more gas during cold days (ie you get a slightly denser gallon of fuel, which will expand to slightly more than a gallon at room temperature).

If the density correction factor is out at your station (or more specifically, at the exact pump you use), you could be getting more or less in the tank than you pay for. I also don't know exactly how the correction works ... some say if you buy gas at the coldest time of day you get a denser gallon. I can see that working if the correction is not actually measuring the fuel temp at the pump but is adjusted based on what amounts to an arbitrary temperature value; a guess, if you will, of what the temp of the fuel is on a given day. I wonder sometimes if that has any bearing on people who report different mileage at different stations.

 

The engine is just a giant air pump. More air in, equals more power out. (increasing the efficiency.) If you don't have to step as hard on the go pedal, to get enough power (as on a more efficient engine) you get better fuel economy. Easy. Sorta....

The point about temp corrected pumps, is a valid one. Trouble is, I am not sure of a reliable way to determine if any given pump does that trick. Not like the folks running the counter are going to know.

 

Just filled the beast at Costco after my post this morning; sticker said corrected to 15C (59F).

I've put about six fills through the 96 so far and have an average of 11.9mi/US gallon. My best was highway at 16, probably 1 tank's worth, the rest is city. Posted limit here (Western Canada) is 110 kmH (70 mph) and the RCMP give you a roadside 10kmH discount when they write a ticket, so everyone drives 120 and fears no-one. The adventurous go faster. So, that 16 mpg is at 75 mph, at 25~40F, which is warmer than normal but it is what we've had so far so there you go.

Not complaining, just reporting, but the truck I had before ... a 77 GMC 350/Turbo 400/3:56 rear with heavy duty emission class engine (over 6000 GVW) which means no emissions, no cat, etc for that year, averaged (over many years) 12/US gallon city and 20/US gallon highway. Weight of that truck was 4200 lbs with me, a tankful, and no cargo in it.
I'd like to equal or better that with the Ram (it's about 400 lbs heavier than the GMC according to the same scale).

I will consider what I've got for the Ram so far a good baseline and so I will play around and see what happens next. Will definitely pop a K&N in, as I always do, and haven't changed oil yet, so 0W-40 Mobil1 will get thrown in perhaps this week. I probably will stop there and see if I can get another good baseline ... maybe a half dozen tankfuls ... and report back.

 

California is its own freakin' planet! I was born and raised there and got out as quick as I could. As did much of my high school graduating class, it seems.

Geographically, the state's a mixed bag. Both the highest and the lowest points in the contiguous US are there and only about 80 miles apart. The bulk of the population, though, lives on relatively flat ground. In and around the population centers the problem for fuel consumption and air quality is commuter traffic and truck traffic around the ports. The fools could solve the commuter traffic problem easily enough, and did it in the summer of '84 during the Olympics but reverted back to their old, stupid ways as soon as the games were over. I wasn't there for it, but everyone I spoke to loved it. Their commute times were cut by 2/3 or so, their weekly fuel bills cut by 2/3 to 3/4, the air was not as filthy, and their overall stress levels much, much lower. I heard many times, "I can actually see the mountains again! I haven't seen them so clearly so often since the early 70's!". All it took was staggered work schedules to the bulk of the working population wasn't on the freeways at the same time.

Anyway, it's easy enough to get better fuel economy out of these old trucks but they'll never compete with lighter vehicles or newer trucks. The best magic gizmos for fuel economy are an air compressor, tire pressure gauge, and a right foot modulated with feedback from a vacuum gauge. Nuthin' to it but to do it.

 

No argument with you about Cali there big guy. Thankfully, I'm where I can see the mtns. all day long. I've lived a good deal in SoCal. It has its lovely spots, but the valley with its smog... yuck.

If you bought your truck for gas mileage, then you better GTFO.