What causes me to have such good mileage in hot weather?

[Compaq888]

I noticed when I drive at night my car can barely do 40mpg. When it's hot out and during the day I get high 40's.

I tried to do the warm air intake on my last car and the mileage actually went down. When I put the stock intake, air filter it went back up to normal.

So what's causing the car to get such good mileage when it's hot out?

[NiHaoMike]

Could it be accelerating warmup?

[Compaq888]

That has little effect on long drives. I have a scangauge 2 so I can see my numbers.

We're not talking about short trips.

[basslover911]

Humidity?

It will "stuff" the air much more than it would be expanding it from being hot and thus a lot less fuel would be injected in.

Also, you cant compare your old car to yoru new car. They all react differently to WAI and other engine mods.

[Metrosexual]

There are several reasons. Bassically a cold engine requires a richer fuel mixture to run properly until it warms up. A choke on a carburetor used to perform this function, now its done seemlessly through the fuel injection system -you won't even feel this happening. Cold weather requires longer warm up times.
2 Cold air is denser during cold weather your engine can take in a greater mass of air, and add the corrosponding greater mass of fuel. this will give you noticable higher engine perfomance but worse gas milage
3 veriables in the weather, rain, snow, impede performance and increase drag on the vehicle, both aerodynamically and mechanically where the rubber meets the road.

[RH77]

The Santa Ana Winds dude.

[Compaq888]

Originally Posted by RH77

The Santa Ana Winds dude.

LOL!

Maybe I should not drive my car at night. jk. Lately we had some really hot days in cali. and my numbers are up there.

[Duffman]

1) Warm air is less dense so there should be less aero drag.
2) You are getting the warm air intake effect.
3) Less warm up time but also, parts are looser, oil is thinner etc.

[Compaq888]

interesting.

[wagonman76]

Originally Posted by Duffman

1) Warm air is less dense so there should be less aero drag.
2) You are getting the warm air intake effect.
3) Less warm up time but also, parts are looser, oil is thinner etc.

Bingo. Like #3, even if the engine is warmed up, other fluids are warmer and flow easier too, like trans fluid, diff fluid, power steering fluid, wheel bearing grease... it all adds up.

Also the air pressure in your tires changes with temperature, so higher temps = higher PSI and less rolling resistance.