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

[vtec-e]

Originally Posted by wagonman76

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

Ah yes, but i check my tires twice a week and keep them at 55psi!

ollie

[cfg83]

Metrosexual -

Originally Posted by 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.

Isn't this the logic behind the CAI (cold air intake)? The goal is to get cool "humid" air into the engine in order to increase the oxygen and thereby increase the amount of fuel injected.

Question: How come some people report better mileage on cold wet days? This sounds like a contradiction to me.

CarloSW2

[PaleMelanesian]

My informal studies show that rolling resistance goes up significantly in warmer weather. Increased glide distance is almost linear with increased temperatures.

That, and faster warmups for all parts - engine, transmission, etc.

[Ford Man]

There are several things that factor into this, driving at night using the lights puts more drag on the alternator, if it's cool enough to need heat the blower will also add more load to the alternator, cooler air is more dense, cooler temperatures effect the viscosity of oil and other fluids. The grease in the wheel bearings will be stiffer causing more rolling resistance. The air pressure in the tires will increase in higher temperatures creating less rolling resistance. The winter blend of gas is already being made which will also effect FE.

[TestDrive]

Originally Posted by Compaq888

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.

How big a drop?

Did the warm air intake eliminate air flow through the MAF (Mass Air Flow Sensor)? That would make FE lots worse.

[12voltsolar]

another reason for the change / drop in FE in colder weather could be the change away from the summer fuel blends.

so poor timing on a real test temperature wise but I just had my MAF replaced and my FE went down? All in the name of getting the check engine light off so my wife would stop asking me about it, lesson if it ain't broke don't pay the mechanic a bunch to not really fix it.

[slurp812]

Originally Posted by 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.

Oil is thicker when cold.

[TestDrive]

Originally Posted by 12voltsolar

I just had my MAF replaced and my FE went down?

MAF needs "cleaned" much more often than it needs "replaced."

Changing MAF implies a reset of the ECU. Typically an ECU will take a few miles (eg 150 mile) to fully recalibrate itself. If you're FE drop is based on a scan-guage or similar reading, give the ECU a little time to tune itself in.

If you've already gone 150 miles or more and the FE is still down more than colder weather would account for, you might want to double check that the mechanic didn't introduce a spec of lint or crude on the new MAF when he installed it.

[Formula413]

I didn't see anyone specifically mention losses from the throttle plate. Since warmer air does not produce as much power, more is needed to produce the same amount of power, thus the throttle plate must be opened wider. Since the throttle plate produces resistance that the engine must overcome to draw in air, the wider it is open, the more efficient the engine will be, all things being equal.

[Compaq888]

Originally Posted by TestDrive

How big a drop?

Did the warm air intake eliminate air flow through the MAF (Mass Air Flow Sensor)? That would make FE lots worse.

A couple mpg. I got 31.4mpg driving 200 miles at night on the freeway with a warm air intake. When I put the stock intake and filter on I would get 38-39mpg. Huge difference if you ask me. This is why i'm keeping everything stock on this car.