Heating Intake Air

The improved fuel economy on warmer days is not from higher intake air temperatures. The warmer the ambient air temperature, the more quickly the car's computer will reduce the high idle associated with startups, the more quickly the automatic transmission will upshift, and the more quickly the emissions controls will go into closed loop operation.

You will get little, if any measurable improvement in fuel economy from heating the intake air temperature. In fact, cold air tends to be denser than warm air so the engine burns fuel more efficiently with cool air than with warm air, which is why people trying to get more power from their engine run cool air intakes out the front of the car or up on the hood.

I would not attribute your increase in mileage with increased intake temperatures. First, make sure that you are not running the defrost mode in the morning which will decrease mileage. Colder air is denser than warm which would equate into higher efficiency in the combustion process. I have noticed this decrease in mileage affecting small engines associated with colder temperatures as well. It could be that the engine displacement being relatively small is very sensitive to loads placed on it, and in turn uses more fuel. Cold outside air temperatures have a direct effect on the viscosity of all lubricants, (engine oil, transmission oil, bearing greases, ect.)usually increasing them, and in turn, increasing engine loads. Temperature swings will even slightly affect your rolling resistance associated with tire pressure. Operating temperatures in cold (winter) conditions can be substantially lower than during warm (summer) conditions. A head wind or tailwind can be a factor as well. It's my opinion that the increase in load for the reasons mentioned increases fuel consumption. I have read no particular data to back this up. I don't think that this would be as noticeable if a larger engine was compared. It will be interesting to read others opinions on this.

Up to a point! If the air is TOO cold, the engine can't get to normal operating temp and doesn't operate as efficiently. Warm air isn't too good, either.

I find that temps between 45-60 degrees gives the optimum performance. Judging by my Mazda, all winter I could barely crack 25MPG, usually LESS, but when we had a week of temps ~52-65 degrees, it jumped up to 29 MPG!

The stoichiometric ratio (optimum air/fuel ratio) for gasoline is 14.7:1 by mass. Simply put, colder intake air offers a higher DENSITY of oxygen (oxygenators) that improve the efficiency (fewer emissions) of the combustion process which in turn equates to a higher energy output of the engine. Colder fuel can also increase efficiency by entering the combustion chamber at a higher density than warmer fuel (racing fuel cool cans). Colder INTAKE air is always beneficial and the colder the better (ram air, inter coolers, ect.) unless we are talking absolute temperatures because it is denser (turbochargers, superchargers, ram air effect). The modern liquid cooled engine will attempt to reach operating temperature set by thermostat temperature choice and coolant system pressure in some instances. Even in extreme cold if the thermostat is operating closed at times it will open enough to prevent overheating in the jackets and then cycle again. (This usually happens one cycle every time we start our cars from dead cold.) Again Hachi, I think it's the load placed on the small displacement engines due to the increased viscosity of lubricants when it's cold outside. But I could be all wrong. IMHO. OBTW, I took the blade off the truck again. ;^)

1. Are you a Physicist or something?!?!

1. Yes, I definitely know the advantages of cold (or cooler) air in the intake of the engine, and the density of cooler air. I was trying to figure out a way to wrap tubing from the A/C around the air intake on my 'Hachiroku' to cool the air heading to the plenum. And, I had a 'cold air intake' on the Tercel. It may not have doen much for HP, but I did notice that off-the-line starts were a LOT smoother after installing it, and my fuel economy went from 38MPG over all to 44-45MPG overall.

2. Put that damn blade back on! They're predicting snow all day Thursday! I'm never going to get my Supra out of storage at this rate!

I think the reduced fuel economy in cold weather is due the longer time it takes for the engine to reach operating temperature, and because the ECT will delay upshifts until the coolant has warmed up.

During the summer months, the formula for fuels change, resulting in poorer fuel economy.

The spring and fall, where temps are warm enough for the engine to warm up quickly, and where summer blend fuels are not in use yet, are when most people get the bet fuel economy.

In the fuel refining process for seasonal changes, do they not formulate winter blends to vaporize/atomize easier (for starts) than summer blends that they try to suppress vaporization/atomization rates? If vaporization is enhanced for winter blends, would there not be fewer BTU's and in turn reduce fuel mileage? Usually a fuel with higher vaporization/atomization rates (more volatility) is refined farther from the beginning natural product (crude oil) and in turn less efficient (fewer BTU's)? An example being the available BTU's in fuel oil compared to gasoline. Interesting Ray. Thanks.

"Ray O" wrote in news:ec5bc$461a892f$44a4a10d$ snipped-for-privacy@msgid.meganewsservers.com:

And the faster the oil heats up and the greater the chance it will get close to 210F, reducing frictional loading on the engine.

By the time the intake air gets into the combustion chamber, it's already about 175F.

Remember the throttle body is heated with coolant bypassed from the block, and radiant heat in the intake plenum and runners add their own heat to the air. Just try to touch the intake runners on a hot engine.

Toyota already does this on many, if not all their models. Even our lowly Tercel has a factory "cold air" intake.

Chemistry is not one of my strong points so I do not really understand the differences between summer and winter fuel blends. A friend is a chemist who works for UOP's R&D department formulating fuels, and he has mentioned that summer fuels burn more cleanly but get slightly less fuel economy, so that was the basis for my statement. If I think of it, I'll try to remember to ask him if more refining reduces BTU content next time I see him.