Cold weather and lower top speed & mpg?

[Gil]

I have noticed over the last few months that my PCX gets better MPG in hot weather than cold foggy weather. But, yesterday I also noticed that my top speed seems to be affected. In the morning heading to school I could barely crack 63 mph, but on the way back with the sun out I could achieve up to 67 mph. My best mpg ratings have been on long hot day rides.

My theory is that the thermostat might have something to do with it. I'm thinking that when it's cold out and the thermostat closes it creates back pressure on the water pump which would suck more power from the engine.

What do you peeps think?
Am I onto something?



Gil

[gn2]

Its more likely that the wind direction/strength were different.
The wind will affect performance far more than changes in temperature.

[DAB]

All IC engines use more fuel in colder weather, it's due to thermodynamics. As for the speed, like GN said could be the wind direction.

[you you]

All IC engines use more fuel in colder weather, it's due to thermodynamics. As for the speed, like GN said could be the wind direction.

It's a teeny scooter.

[DAB]

All IC engines use more fuel in colder weather, it's due to thermodynamics. As for the speed, like GN said could be the wind direction.

It's a teeny scooter.

Yes but the same laws apply, I see seasonal variation on all my bikes and car.

[TheMaverick]

All IC engines use more fuel in colder weather, it's due to thermodynamics. As for the speed, like GN said could be the wind direction.

It's a teeny scooter.

Yes but the same laws apply, I see seasonal variation on all my bikes and car.

Cooler air is more dense - so it requires more fuel molecules to get the correct fuel/air mixture. Performance should be increased because of this though.

[gn2]

Denser air means increased drag.

[TheMaverick]

Denser air means increased drag.

Yes, but assuming a constant pressure, the change is proportional to ABSOLUTE temperature so in normal winter <> summer variation the change is negligible.

[springer1]

Cooler air is more dense - so it requires more fuel molecules to get the correct fuel/air mixture. Performance should be increased because of this though.

Yep, the cooler and drier the air, the more fuel required for the mix - look up "RAD factor" and there's a lot of info - Relative Air Density.

https://wahiduddin.net/calc/calc_hp.htm

[DAB]

A given amount of fuel has a fixed amount of energy. If the ambient temperature is lower, more of the fuel is used to generate heat giving less for mechanical work.

[dgnyberg]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

[djbass]

Gil, lowering the temperature does not have a strong influence, because the difference is 10-20 degrees for a fuel-injected engine - a slight error. Computer injector always generates the correct composition of the combustible mixture. Warm up the engine to operating temperature is also happening around the same time - 2-3 mile track, so the engine is working correctly with sufficient viscosity oil, including gear-drive CVT.

[homie]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

Yea, I remember dad running up the RPM and pouring a glass of water down the carburetor on a old chevy claiming it knocked the carbon off the pistons whist white smoke billowed out the tailpipe. That must have been a fad too because I never see anyone doing it these days... he crazy

[you you]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

Yea, I remember dad running up the RPM and pouring a glass of water down the carburetor on a old chevy claiming it knocked the carbon off the pistons whist white smoke billowed out the tailpipe. That must have been a fad too because I never see anyone doing it these days... he crazy

I can remember that. Not on a Chevey but a Hillman Imp.

[dgnyberg]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

Yea, I remember dad running up the RPM and pouring a glass of water down the carburetor on a old chevy claiming it knocked the carbon off the pistons whist white smoke billowed out the tailpipe. That must have been a fad too because I never see anyone doing it these days... he crazy

My dad did the same thing. I asked him once about it and he showed me how well it worked.
He took a white shop cloth and held it over the exhaust pipe. It came off fairly clean.
He did it again as I dribbled the water down the carb and the cloth got quite black from the steamed off carbon.
Was it from the engine or the exhaust, I don't know for sure, but it did do something.
It's kind of hard to pour water through today's fuel injectors, LOL!!

Dave

[you you]

I remember years ago people installing water vapor-injection systems in their cars to increase mileage.
It seems that increasing the humidity of the intake air better incorporates the atomized fuel.
It may have just been another fad, too.

Yea, I remember dad running up the RPM and pouring a glass of water down the carburetor on a old chevy claiming it knocked the carbon off the pistons whist white smoke billowed out the tailpipe. That must have been a fad too because I never see anyone doing it these days... he crazy

My dad did the same thing. I asked him once about it and he showed me how well it worked.
He took a white shop cloth and held it over the exhaust pipe. It came off fairly clean.
He did it again as I dribbled the water down the carb and the cloth got quite black from the steamed off carbon.
Was it from the engine or the exhaust, I don't know for sure, but it did do something.
It's kind of hard to pour water through today's fuel injectors, LOL!!

Dave

That's it. It was good fun

[djbass]

You guys are kidding about water in the carb.
In the Soviet Union in the 70-80-ies also poured a drop of water in the carb to save fuel, now haven't heard of it

[Gil]

I think you peeps are correct. I would have to do some AB, BA testing with different temperatures, but not wind. I'm in Santa Cruz county, California and we always get a breeze from the ocean. Any kind of wind effects are noticeable on the PCX simply because of the small size. I was hopping .

[Gil]

Thanks for the feedback by the way.


Gil

[TheMaverick]

A given amount of fuel has a fixed amount of energy. If the ambient temperature is lower, more of the fuel is used to generate heat giving less for mechanical work.

Doesn't quite work that way as what we're trying to achieve is a change in pressure (or pressure ratio). And a lower temperature also gives a more dense charge and the lower temp also makes for more efficient combustion. Quite a few factors influencing things, but generally cooler is better hence the reason intercoolers are used on many turbocharged engines to increase power and efficiency.