Gas mileage gone WAY down

[HaulinAshe]

Recently did the Barbarian Mod and tweaked the settings up 7 points. Noticed a small decrease in fuel mileage and a nice improvement in throttle transition. But recently, within the past month or so, my fuel mileage has gone to crap! We're talking from an average of about 44 MPG all the way down to 34 MPG.

Plugs are in almost new condition. Everything seems fine on the bike. Bike is making lots of horsepower, as is expected in colder air. Just wondering if the average temp shift from 80-90F, down to the 50-60F range normally produces that much of a fuel consumption change in the FJR?

Experienced voices anyone?

 

[Ignacio]

Change from summer gas formulation to winter formulation through the refineries? That and I think some areas bump up the alcohol content in the colder weather.

 

[Bikewhore]

This happens every year. I've asked the same question. I think it has probably something to do with the bike taking much longer to warm up. I tried factoring in the additional drag of textile, weigh of the layers I wear and the coefficient drag of falling leaves. I think it's the warm up thing.

 

[twowheelnut]

Change from summer gas formulation to winter formulation through the refineries?. That and I think some areas bump up the alcohol content in the colder weather.

...and that's the correct answer. 5 MPG, in my case.

 

[radman]

Some cities have a EPA mandate to alter fuels for winter use-the TC area is one of these, EPA mandates 2% oxygen in summer, 2.7% in winter. Naturally, this means less go juice and more of Our Mother the Earth Special Extract, resulting in poor mileage, especially when combined with longer cold start enrichment. If one does a lot of short trip stuff, mileage will go down accordingly. It's amazing how quickly an engine commonly accused of being such a hot runner will cool down to the point of requiring the whole cold start cycle to re-engage in colder weather-that being in the neighborhood of 30-35 degrees or less. I've seen it happen after sitting for 10 minutes or so.

 

[conwest]

...air temperature, pure and simple. In the summer we get around 62-64 MPG (Imperial gallons that is...also read 160oz) when its 30- 40`C and drops to around 58 mpg in the fall when its only 20`C. Always bin the rule...colder it is, the worse the mileage! :blink:

 

[Ignacio]

...air temperature, pure and simple. In the summer we get around 62-64 MPG (Imperial gallons that is...also read 160oz) when its 30- 40`C and drops to around 58 mpg in the fall when its only 20`C. Always bin the rule...colder it is, the worse the mileage! :blink:

And what law of physics is that? Do you have documentation somewhere?

I mean, I buy into the mixture when it relates to warming up a bike, but I don't buy it has a big impact.

 

[HaulinAshe]

Guess I'm just too used to jets. Damn FI actually corrects for air temp and density. I usually just grab a number or two bigger, shove it in and twist hard!

 

[ejworthen]

...air temperature, pure and simple. In the summer we get around 62-64 MPG (Imperial gallons that is...also read 160oz) when its 30- 40`C and drops to around 58 mpg in the fall when its only 20`C. Always bin the rule...colder it is, the worse the mileage! :blink:

And what law of physics is that? Do you have documentation somewhere?

I mean, I buy into the mixture when it relates to warming up a bike, but I don't buy it has a big impact.

From my experience, what conwest is saying is right. I work with gas turbines and see this happen all the time. We get a higher output from them in cold weather but they also consume more fuel. I can see this since the fuel is metered as it is consumed.

The way it was explained to me is it has to do with the density of cold air. Colder air is much more dense so more fuel is added to obtain the correct fuel/air ratio. You would think you would get more power and would then have to back off the throtte but it doesn't work that way. I don't have a really good explanation since this is something I don't know much about.

 

[Ignacio]

I don't think turbines are the same as internal combustion in this case. Density is adjusted for the O2 sensor and changes mixture. I think it's a very small x, but can't find the math. I think the fuel composition is the big X in the equation.

 

[cota95]

The last three weeks my mileage has been down and I thought it was because of my right hand, but maybe it was something else... :glare:

 

[ejworthen]

I don't think turbines are the same as internal combustion in this case. Density is adjusted for the O2 sensor and changes mixture. I think it's a very small x, but can't find the math. I think the fuel composition is the big X in the equation.

Well I think you're wrong. Anything that burns fuel would be effected in the same way. Whether it be a turbine, internal combustion engine, etc. I tried to find more info but have been unable to locate anything as of yet.

They only statement I can find on the internet is that in cold weather gas mileage can be reduced by as much as 50%. That would indicate to me cold weather is more of a factor than fuel composition. They do not indicate what factors of cold weather contribute to the reduction in mileage other than the engine not reaching operating temperature. They do state that an engines efficiency is reduced in cold weather.

 

[Ignacio]

I don't think turbines are the same as internal combustion in this case. Density is adjusted for the O2 sensor and changes mixture. I think it's a very small x, but can't find the math. I think the fuel composition is the big X in the equation.

Well I think you're wrong. Anything that burns fuel would be effected in the same way. Whether it be a turbine, internal combustion engine, etc. I tried to find more info but have been unable to locate anything as of yet.

They only statement I can find on the internet is that in cold weather gas mileage can be reduced by as much as 50%. That would indicate to me cold weather is more of a factor than fuel composition. They do not indicate what factors of cold weather contribute to the reduction in mileage other than the engine not reaching operating temperature. They do state that an engines efficiency is reduced in cold weather.

How about a source my friend?

I meant to say mixture and not density there. I don't think turbines have O2 sensors and adjust mixture with a feedback loop.

Gasoline has 125,000 BTU's per gallon and ethanol has 84,400. Gasoline that is amended with 10% ethanol like done in some regions during the winter months will get 3.3% less mileage. Source

I would agree that the colder air will be more dense and require more gasoline, but it will also have a similar increase in the energy the charge has....which seems to me would offset it more or less. I still think temperature difference is a smaller factor than this, but look forward to any math or documentation supporting it.

If anything the colder air's density would increase wind resistance and that one would not be gained back, but I think it would be a fairly small variable unless cruising around at FJR nominal speeds.

 

[Big Sky]

Cold temperatures will increase drag and resistance to turning of all driveline components as lubes stiffen: transmission, output gears, drive shaft, differential, wheel bearings and axels, etc. Living in Montana, sometimes when it's REALLY cold, the clutch won't even disengage. Or you can put it into neutral at a roll and there is so much drag in drive components that the vehicle will roll to a stop almost as if the brakes were being applied. Of course, this improves as all components warm up. And yes, mileage will go down substantially as it takes more power to make things move and overcome the cold-induced stiffness.

 

[The Professor]

My gas mileage dropped drastically on my car once. It turned out the thermostat was stuck open so the engine never warmed up. This effect was magnified in cooler weather. My advice is to check the thermostat.

 

[HaulinAshe]

If anything the colder air's density would increase wind resistance and that one would not be gained back, but I think it would be a fairly small variable unless cruising around at FJR nominal speeds.

And we all know that I would NEVER cruise around at FJR nominal speeds.

Good advice on the thermostat, but no problem there. Engine comes up quickly to two bars in the cold. Has a hard time making it to three bars unless sitting in traffic.

 

[Knifemaker]

Well, everyone should be happy that their theory is correct, as ALL of these factors contribute to poor MPG figures in the cold.

Wind resistance is higher, and there is usualy higher winds in the winter also to move against.

Cold air is more dense and does require more fuel, yes you are getting more power...but its doing you no good as your bike sits there running while it warms up. Warm up time offers the worst fuel eccomomy already, extending it and coupling it with the extra fuel only makes it more so.

We do have air tempature sensors on our bikes? Most EFI units do, so they would be squirting more fuel into our engines if the air is cold, even when the engine is 'warmed up"

I am not familar with the diffrences in fuels, but if "winter gas" produces less power than "summer gas" per volume, then factor that in too..

Extra weight from 'heavy' winter clothes would be very small, but their poorer aerodynamics would be worth counting.

So really it is all these things combined that give us crappy fuel ecconomy when it is cold, but the primary offender is that pre ride warm up....and our programmed wrists that make the bike perform the way we are used to feeling it...wind resistance and air density be damned..............

KM

 

[Ignacio]

Well, everyone should be happy that their theory is correct, as ALL of these factors contribute to poor MPG figures in the cold.

I'm sure they do to, but where's the math?

I just found out that winter blend also has increased amounts of butane to increase vapor pressure and volatility. Instead of 2% for summer, it may have 10% butane for winter. The BTUs per gallon of butane are 104,000 vs. the 125,000 for gasoline so there's another 6.6% reduction in mileage I believe? It seems winter gas is a seriously different critter than the summer stuff.

 

[Mississippi]

Air temperature and barometric pressure have a big effect on gas mileage and horesepower produced. As stated in the above posts, colder air means more dense air, which means more oxygen molecules are present in a given cubic foot of air. The FI system has to add more fuel in order to to keep the correct fuel/air mixture, which is why the FI sytem computer needs to know what the intake (not ambient) air temperature is. True, this denser fuel/air mixture will allow your engine to produce more horsepower, but it is not free because you are adding more fuel per mile. The colder , denser air "allows" you to have a more dense charge to each cylinder, which results in increased horsepower. This is why the racer boys try to cool the intake charge to their engines, it allows them to make more horsepower, but it takes more gas.

Atmospheric pressure also affects the intake charge to each cylinder. Higher barometric pressure means more dense air, which again requires more fuel to keep the fuel/air ratio correct. Low pressure means less dense air, which means fewer oxygen molecules are present in a cubic foot of air, which means less fuel is required. This is why horsepower is reduced as the altitude you are riding at increases. The greater the altitude , the lower the barometric pressure is, the less dense the air is, the less fuel can be shoved into each cylinder and power is reduced accordingly.

Humidity also affects mileage/horsepower - but to a much lesser degree than temperature and pressure.

OK - 'bout the longest post I ever made on any forum