MPG decreasing

schrecke · Oct 5, 2007

I watch my fuel mileage pretty regularly on all my vehicles as it helps to sometimes provide early diagnoses, etc.

Having said that, my normal mileage on the FJR commuting to work is 36.X mpg every tank. The past few weeks it has gone down to 33, which is about an 8% drop. I want to know why. I use the same gas station all the time.

Right around the time it started to get cooler around these parts (now 50's F in the morning, but still 60s/70s afternoon) I changed my plugs to the Iridium NGK CR8EIX. Old plugs looked just fine, light brown and dry, but it had been about 9K so I changed them. Since that time I have seen the mileage decrease consistently. Air filter looks fine.

2005 ABS w/ PCIII (O2 disconnected)

Any thoughts on this? :huh:

twowheelnut · Oct 5, 2007

Did MA switch to winter gas? My mileage drops from 45 to 40 with Cali's winter blend.

schrecke · Oct 5, 2007

twowheelnut said:
Did MA switch to winter gas? My mileage drops from 45 to 40 with Cali's winter blend.

Very well could be. Someone else suggested that. I didn't realize it would have such an effect

Fred W · Oct 5, 2007

I've noticed a lot of pumps in New England have switched from 5 to 10% ethanol. That'll knock the ole mpg down some.

schrecke · Oct 5, 2007

Fred W said:
I've noticed a lot of pumps in New England have switched from 5 to 10% ethanol. That'll knock the ole mpg down some.

Everything near me has been 10 % Ethanol for quite some time now.

Bustanut joker · Oct 5, 2007

Nah, it's the age old problem of the fuel density being lower on account of the lower temperatures.

What? you fergot that silly thread already? Shame on ya doublenut. :lol:

:jester:

Fred W · Oct 5, 2007

schrecke said:
Fred W said:

I've noticed a lot of pumps in New England have switched from 5 to 10% ethanol. That'll knock the ole mpg down some.

Click to expand...

Everything near me has been 10 % Ethanol for quite some time now.

OK, in that case, I vote for the MRFWU. It sure sounds like it's the plugs. Only one way to tell.

huron52 · Oct 5, 2007

twowheelnut said:
Did MA switch to winter gas? My mileage drops from 45 to 40 with Cali's winter blend.

California using a WINTER blend? You mean it get's cold there? :huh:

shuswaper · Oct 5, 2007

Around here in our summer, at it`s hottest, I routinely get 62-64 mpg (Imperial gallon). Last couple of weeks with temps in the range of 8-15`Celsius, I am now getting 56-58 mpg. The gasoline formulation has not changed. It`s strickly the low airtemps that is causing worsenning fuel efficiency. It`s an age old fact of life in the internal combustion world.

h34r:

twowheelnut · Oct 5, 2007

huron52 said:
twowheelnut said:

Did MA switch to winter gas? My mileage drops from 45 to 40 with Cali's winter blend.

Click to expand...

California using a WINTER blend? You mean it get's cold there? :huh:

I know... If I remember right, the baseline test gas for RVP is at 1000F, so if you drop to wintertime highs in the 60's, that's a significant change. I ain't no expert on this - far from it - and I'm sure someone else can better define the issue, but I've been trying to read up on some of this stuff...

An EPA snippet:

As gasoline evaporates, volatile organic compounds (VOC’s) enter the atmosphere and contribute to ozone formation. Gasoline’s propensity to evaporate is measured by Reid vapor pressure (RVP). In order to control VOC emissions, the Federal Clean Air Act Amendments of 1990 require that all gasoline be limited to an RVP maximum of 9.0 psi during the summer high ozone season, which the Environmental Protection Agency (EPA) established as running from June 1 to September 15. The Act also authorized the EPA to set more stringent standards for nonattainment areas. As a result, EPA limits areas designated as “high volatility non-attainment” to a maximum RVP of 7.8 psi during the high ozone season. Some States elected to require even more stringent restrictions to achieve local clean air goals, and require 7.2- and 7.0-psi gasolines.

LA further tightens the screw as does Phoenix, San Fran and other major metro west/west coast areas.

Bustanut joker · Oct 5, 2007

Oh Man ain't that jus swell :blinksmiley:

Along comes a thread we can piss all over an you get all Bill Nye on us. :close_tema:

Thanks pops :****:

:jester:

odot · Oct 5, 2007

I think nutsquared is trying mind his p's and q's.

twowheelnut · Oct 5, 2007

odot said:
I think nutsquared is trying mind his p's and q's.

Nope, not me.

Huck Fonda · Oct 7, 2007

I hope another opinion is allowed here. The RVP discussion is right on. There are regional and seasonal blends of fuel used just about eveywhere, but there is another factor as well.

Cold weather means denser air, right? Denser and colder air are interpreted by the ECU as conditions that need more fuel. As support for this idea, my bike runs much better in cooler weather than in the heat of summer. The "genie" in the box adds extra fuel when it's cold, and takes some away when the air is hotter and therefore less dense. This last (since I have not done the CO adjustment yet) means that my bike runs much worse in the summer.

RVP coes into play seasonally because at colder temps (denser air) the fuel dosn't vaporize a well, which could lead to hard starts. The gas gods, inrease RVP (higher rate of vaporization) in the winter blends to help ensure easier starting. I think this, though, also means that the fuel can naturally evaporate quicker, which combined with the ECU adjustment results in a poorer fuel economy calculation.

I have a chart of national RVP limits at my desk, will try to remember to post it here Monday.

Used to be with carburetors that runs bad hot = too rich, and runs bad cold = too lean. Now with temp and pressure sensitive computers, it's gone 180 on us.

schrecke · Oct 8, 2007

Huck Fonda said:
I hope another opinion is allowed here. The RVP discussion is right on. There are regional and seasonal blends of fuel used just about eveywhere, but there is another factor as well.
Cold weather means denser air, right? Denser and colder air are interpreted by the ECU as conditions that need more fuel. As support for this idea, my bike runs much better in cooler weather than in the heat of summer. The "genie" in the box adds extra fuel when it's cold, and takes some away when the air is hotter and therefore less dense. This last (since I have not done the CO adjustment yet) means that my bike runs much worse in the summer.

RVP coes into play seasonally because at colder temps (denser air) the fuel dosn't vaporize a well, which could lead to hard starts. The gas gods, inrease RVP (higher rate of vaporization) in the winter blends to help ensure easier starting. I think this, though, also means that the fuel can naturally evaporate quicker, which combined with the ECU adjustment results in a poorer fuel economy calculation.

I have a chart of national RVP limits at my desk, will try to remember to post it here Monday.

Used to be with carburetors that runs bad hot = too rich, and runs bad cold = too lean. Now with temp and pressure sensitive computers, it's gone 180 on us.

Reminder to post up that chart...

Huck Fonda · Oct 8, 2007

schrecke said:
Huck Fonda said:

I hope another opinion is allowed here. The RVP discussion is right on. There are regional and seasonal blends of fuel used just about eveywhere, but there is another factor as well.
Cold weather means denser air, right? Denser and colder air are interpreted by the ECU as conditions that need more fuel. As support for this idea, my bike runs much better in cooler weather than in the heat of summer. The "genie" in the box adds extra fuel when it's cold, and takes some away when the air is hotter and therefore less dense. This last (since I have not done the CO adjustment yet) means that my bike runs much worse in the summer.

RVP coes into play seasonally because at colder temps (denser air) the fuel dosn't vaporize a well, which could lead to hard starts. The gas gods, inrease RVP (higher rate of vaporization) in the winter blends to help ensure easier starting. I think this, though, also means that the fuel can naturally evaporate quicker, which combined with the ECU adjustment results in a poorer fuel economy calculation.

I have a chart of national RVP limits at my desk, will try to remember to post it here Monday.

Used to be with carburetors that runs bad hot = too rich, and runs bad cold = too lean. Now with temp and pressure sensitive computers, it's gone 180 on us.

Click to expand...

Reminder to post up that chart...

Could use some help with posting up a pdf. file. Until then, this is where I got it. https://www.epa.gov/otaq/regs/fuels/420b07007.pdf

TruWrecks · Oct 9, 2007

Yep. Cold temps = lower fuel mileage.

My truck, which got 18MPG when the temp was in the 70's, is now getting 15MPG on the freeway. With a 27 gallon tank it gets really expensive to drive a few hundred miles.

Harald · Oct 10, 2007

My mileage goes down every winter here in the Seattle/Tacoma WA area, but I don't think the coldness is the primary reason. In order to meet EPA air quality standards in the winter, all gas stations have to sell oxygenated fuel to lessen emissions. This fuel yields considerably less fuel economy.

I know in the past I used to fill my truck in Wenatchee (eastern WA) and would get much better gas mileage in the winter with their fuel.

Ignacio · Oct 10, 2007

It's like this thread is new every season about this time. Then in the Spring we have another companion thread where somebody discovers they got a tank with incredible mileage.

...it's mildly entertaining to watch and has become a sign of seasonal change to me as much as leaves dropping or fresh green poking out of the soil.

MPG decreasing

Help Support Yamaha FJR Motorcycle Forum:

Well-known member

R.I.P. Our Motorcycling Friend

Well-known member

1 Wheel Drive

Well-known member

Well-known member

1 Wheel Drive

Well-known member

Well-known member

R.I.P. Our Motorcycling Friend

Well-known member

CC member # 17,----- DUP member # 7, mensa club m

R.I.P. Our Motorcycling Friend

Well-known member

Well-known member

Well-known member

Still chewing thru the Restraints

"Superior Gen 4" Rider

Intramural Culture Warrior

Similar threads

Join the conversation!

Join today and get all the highlights of this community direct to your inbox. It's FREE!