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I got a message from someone concerned about their gas mileage. I typed up a long reply and then decided that maybe I should post it for the general population to see, so here it is.
Fred
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You probably need to do some actual MPG calculations and see what you get. I typically get between 90 to 100 miles when the gauge hits the halfway mark. Typical mileage on a GL1800 is about 32-38mpg, depending on bike speed, wind speed/direction, temperature, load, tire pressure/type, altitude etc. I have gotten as low as 30 MPG while riding at higher speeds. Some folks will report getting 40 or even 42mpg on internet boards. If you ever ride with any of these guys you will understand why their mileage is so high. They ride nice and easy and don’t generally ride as fast as others. Personally, I can’t ride that way, but that is just me. I like to go fast and Texas highways make that easy to do.
Speed has a big impact on mileage, as does how hard you accelerate and brake (which also affects your tire mileage greatly). Colder winter temperatures also cause a drop in mileage. That is normal. Also, remember the lower your local altitude, the worse your mileage will be. Someone who lives in Colorado may get 5 or even 10 mpg higher than someone who lives near the coast at sea level. This is because the bike has a barometric sensor (BARO sensor) that tells the ECM to lean the mixture as the altitude increases. This also means that even a low or high pressure front can affect your mileage slightly.
You really don’t get a good data point comparing your mileage with someone else’s as there are just so many variables at work. Also, remember that wind drag has a pronounced affect on mileage. Aftermarket windshields are notorious for causing gas mileage reduction. So do highway pegs with size 12 boots hanging on them, and mirror air deflectors and baker wind wings. Anything that is in the airstream sucks horsepower from the engine and reduces mileage.
One real easy thing you can do yourself is to pull the spark plugs and check the color of them. If they are clean, then your bike is probably running ok. If they are dark or sooty, then you are definitely running too rich. This is probably the first thing I would do if I were you. Here are some photos of mine, this is about what they should look like:
http://www.pbase.com/image/14813796
There are two basic components to suspect if your bike is running rich and/or your gas mileage is abnormally low. The first things are the oxygen sensors. Many have reported having one or more (there are two in the bike) bad o2 sensors and that it impacted their mileage. I replaced both my o2 sensors about a week ago and my gas mileage went from about 32mpg to about 35 or 36 mpg. My o2 sensors had 40K miles on them. Standard advice on 02 sensors is to replace them sometime around the 40-50K mile mark. Here is a link to my oxygen sensor replacement photos:
http://www.pbase.com/fredharmon/o2sensors
The second component to check is the fuel pressure regulator. It is supposed to vary the fuel pressure in the fuel rail from about 41psi to as high as 50psi during high fuel demand situations. It isn't easy, but you can put a gauge on the fuel rail and check the fuel pressure at idle. It should be about 41 or 42 psi. If it is 45 or higher, then you may have a bad regulator. Here is a link to my fuel pressure testing I did:
http://www.pbase.com/fredharmon/fuelpressure
Also, depending on the mileage on your bike, you might want to think about replacing the air filter. A clogged air filter will reduce mileage.
In closing, if your mileage is anything over about 30mpg, there probably is nothing wrong with the bike. Monitor it over a few months closely and see how it behaves. As the weather warms up, it should improve by a few MPG. You can do things to help it, like keeping fresh plugs, oil, and airfilters in the engine and changing the o2 sensors when the bike gets near the 50k mark. Keep tire pressure correct, and don't add aftermarket devices that increase parasitic drag. And if you really want to improve your mileage, keep your speed under 60mph (if you can, you are a better man than me!)
Fred
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
You probably need to do some actual MPG calculations and see what you get. I typically get between 90 to 100 miles when the gauge hits the halfway mark. Typical mileage on a GL1800 is about 32-38mpg, depending on bike speed, wind speed/direction, temperature, load, tire pressure/type, altitude etc. I have gotten as low as 30 MPG while riding at higher speeds. Some folks will report getting 40 or even 42mpg on internet boards. If you ever ride with any of these guys you will understand why their mileage is so high. They ride nice and easy and don’t generally ride as fast as others. Personally, I can’t ride that way, but that is just me. I like to go fast and Texas highways make that easy to do.
Speed has a big impact on mileage, as does how hard you accelerate and brake (which also affects your tire mileage greatly). Colder winter temperatures also cause a drop in mileage. That is normal. Also, remember the lower your local altitude, the worse your mileage will be. Someone who lives in Colorado may get 5 or even 10 mpg higher than someone who lives near the coast at sea level. This is because the bike has a barometric sensor (BARO sensor) that tells the ECM to lean the mixture as the altitude increases. This also means that even a low or high pressure front can affect your mileage slightly.
You really don’t get a good data point comparing your mileage with someone else’s as there are just so many variables at work. Also, remember that wind drag has a pronounced affect on mileage. Aftermarket windshields are notorious for causing gas mileage reduction. So do highway pegs with size 12 boots hanging on them, and mirror air deflectors and baker wind wings. Anything that is in the airstream sucks horsepower from the engine and reduces mileage.
One real easy thing you can do yourself is to pull the spark plugs and check the color of them. If they are clean, then your bike is probably running ok. If they are dark or sooty, then you are definitely running too rich. This is probably the first thing I would do if I were you. Here are some photos of mine, this is about what they should look like:
http://www.pbase.com/image/14813796
There are two basic components to suspect if your bike is running rich and/or your gas mileage is abnormally low. The first things are the oxygen sensors. Many have reported having one or more (there are two in the bike) bad o2 sensors and that it impacted their mileage. I replaced both my o2 sensors about a week ago and my gas mileage went from about 32mpg to about 35 or 36 mpg. My o2 sensors had 40K miles on them. Standard advice on 02 sensors is to replace them sometime around the 40-50K mile mark. Here is a link to my oxygen sensor replacement photos:
http://www.pbase.com/fredharmon/o2sensors
The second component to check is the fuel pressure regulator. It is supposed to vary the fuel pressure in the fuel rail from about 41psi to as high as 50psi during high fuel demand situations. It isn't easy, but you can put a gauge on the fuel rail and check the fuel pressure at idle. It should be about 41 or 42 psi. If it is 45 or higher, then you may have a bad regulator. Here is a link to my fuel pressure testing I did:
http://www.pbase.com/fredharmon/fuelpressure
Also, depending on the mileage on your bike, you might want to think about replacing the air filter. A clogged air filter will reduce mileage.
In closing, if your mileage is anything over about 30mpg, there probably is nothing wrong with the bike. Monitor it over a few months closely and see how it behaves. As the weather warms up, it should improve by a few MPG. You can do things to help it, like keeping fresh plugs, oil, and airfilters in the engine and changing the o2 sensors when the bike gets near the 50k mark. Keep tire pressure correct, and don't add aftermarket devices that increase parasitic drag. And if you really want to improve your mileage, keep your speed under 60mph (if you can, you are a better man than me!)