Has the higher temp. bring better MPG for you?

[M45Runner]

Recently, with the warmer weather, I was expecting to get better mileage- which is the case for last year. But, it seems this year, it is not happening.

I am in Texas, so now it is already in the mid 70s and I still get the same mileage as in winter (when it is average around 30-40). What is the deal here, does the federal changed the gas content and added more ethonal with the summer fuel?

[NightWatch]

Actually colder weather brings better performance and gas mileage....thats why people put cold-air intakes on their cars.

[tigerclaws1318]

In colder weather many people tend to let their car warm up before driving off which decreases gas mileage.

[83wildcat]

I've always found that I get a drop in MPG in colder weather on my other cars & motorcycles. It could be that when the engine starts colder and operates in colder outside temperatures it takes longer to reach its maximum efficiency temperature. While it’s running at lower efficiency it’s getting lower MPG. This would be compounded by short trip/commutes where the engine perhaps never reaches the maximum efficiency temperature. My commute is only 8 mile each way.

Another thing I've noted is the effect of the climate control system in my M35X. If it’s set to auto, when the heat is on the a/c is also on, which adds a drag on the engine. My last tank of gas I haven't had my heat on and I'm noticing an improvement in MPG from low 17's (pretty consistent over 6 tank fulls) to high 18's (first tank so only limited data so far). My commutes are the same (28 mph avg speed) and outside temperature is about 10 degrees warmer (I wouldn't think 10 degrees should make a that much of a difference) so the only other major difference is that I'm not running my a/c compressor with heat. Of course in hot weather the a/c is being used, but perhaps the better engine efficiency off-sets a the loss due to running the a/c compressor resulting in a net zero change compared to driving when it is "warm" with no a/c.

Also difference between winter fuel mixtures and summer fuel mixtures may impact MPG.

Bottom line, my personal experience is that I get lower MPG in the winter.

[M45Runner]

Actually colder weather brings better performance and gas mileage....thats why people put cold-air intakes on their cars.

I hope you are joking. CAI take in colder air into the engine - it does not matter what the outside temperature is.

Engines like to run hot, when it is warmer, the engine is more efficient and all the lubricate / joints have less resistance, hence improve efficiency. With my other cars (as well as the M45 in the past), I always get better mileage when warmer.

So, if you guys have not noticed this trend yet, there is definitely something changed.

[NightWatch]

The outside temperature has little to do with your engine maintaining normal operating termperatures. It may take a few mintues longer for your engine to warm up if its 20 degress outside versus 70 degress but when it does the component parts function with the same amount of ease and friction. What does matter is the temperature of the fuel and the air being taken into the combustion chamber. Warmer air is less dense and doesn't combust as well when mixed with fuel and yeilds less power. Similarly warm fuel is also less dense and is less effecient. This is why common performance mods try and create as cool an air/fuel mixture entering into the manifold as possible. This is why engineers try and design manifolds to run as cool as possible sitting on top of a hot engine.

Now if you're the type of person that lets your car warm up for 20 minutes while you are inside finishing your coffee on a cold day, I can see why you may not get as good gas mileage, but otherwise your mileage and performance should bet better in cooler weather.

[M45Runner]

Well, the outside temperature do affect how efficient your engine is running.

First, it will take longer for the engine to reach optimum temperature.Second, it will use excess heat to maintain the temperature - especially when you are moving above 40mph.

Also, when it is warmer outside, it takes less time for all the joints & moving part to warm up, which also improve efficiency.

Yes, when it is warmer, there are less air and fuel injected into the engine, thus the performance will drop, but not MPG, while it will generate less power, it also use less fuel (if you are maintaining the same RPM).

So, overall, the MPG should improve, providing the same driving habit and fuel content.

[philb]

M45Runner:

I am thinking it would take basically the same amount of fuel to produce the amount of energy required to move your car regardless of the ambient temperature. Its all about BTU's produced. (The internal combustion engine is a thermal machine) A gallon of gasoline makes 125,000 BTU's (midgrade) .

I guess the argument could be made that the rpms could conceivably go down a bit due to denser air and more fuel per stroke...but I have a difficult time thinking that it would make more than just a few points difference. Note that since air is denser in colder weather, wouldn't aerodynamic losses increase to offset any efficiencies gained? Basically I would think that gas in equals BTU's out, regardless of how many strokes it takes to do the work.

You're right, though, about the less power in the summer, and more power due to denser air (and more fuel) to get more power in winter. I don't think your fuel mileage will go up in the winter...I think the rpms may go down a little, since it's possible to use a little more gasoline per stroke due to denser air.

I can't ever get good gas mileage due to the density of my right foot.I average about 19 mpg on my 03 M45. The best I've ever gotten was the weekend I drove it home from Miami, I got 24 mpg! I've never seen that since!

[M45Runner]

M45Runner:

I am thinking it would take basically the same amount of fuel to produce the amount of energy required to move your car regardless of the ambient temperature.

The amount of force generated + heat produced by the same amount of fuel will be the same - true. However, in warmer weather, you got better lubrication and requires less heat to reach and maintain optimum operating temperature, I would assume this will give you more efficiency.

But, according to what everyone else is saying here, there is not really any noticeable gain in MPG due to temp. changes, so it could just be my imagination maybe

[InfinitiMe]

Doesn't look like it. But then my MPG is constantly reading just over 18. If I drive with cruise control 90% of the trip i can get up to 20-21. Normal driving, on a 46 mile round-trip, with about 70% of those on highway, I can't even reach 19. Hasn't changed and I've been through 1 summer and 1 winter