Calibrate Garmin Fuel Flow Meter?

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Calibrate Garmin Fuel Flow Meter?

Postby Hydraulicjump on Wed Sep 13, 2017 8:36 am

On our last boat (r-27), the Garmin 5212 accurately measured remaining fuel, based on the Yanmar read out of fuel flow. Our new-ish tug (R-29CB) has the 7212 Garmin display and, while infinitely better than the Volvo gage, it is consistently off. I discovered this on a long trip to Desolation Sound and back where I filled the tank each time (ouch, Canada, your fuel is expensive) and compared it to the Garmin estimate. I got a consistent difference of 5%, meaning it took 5% more fuel to fill the tank than the Garmin calculated.

Really, this is no big deal as long as you fill the tank every time and are aware of the difference. But it adds up over time if you are a "put in 40 gallons and go" type because each incremental 5% error has your tank with less fuel than you think. Ten cycles of "40 and go" and you have 20 gallons less than you thought.

Most of us are real careful about this and stick to the one third rule (never let your tank get lower than 1/3 when out cruising), but it is something to keep in mind when in a situation where you might have to push it.

This is a long-winded way to ask if there is a way to calibrate the fuel flow hand off between a Garmin and the Volvo to make this more accurate.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby Red Raven on Wed Sep 13, 2017 12:41 pm

Do you have a Webasto Diesel furnace? The fuel used by the Webasto does not run through the Volvo flow meter so that could explain some of the error.
Last edited by Red Raven on Wed Sep 13, 2017 3:02 pm, edited 1 time in total.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby bill46 on Wed Sep 13, 2017 2:38 pm

Generator also does not go through Volvo.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby NorCal on Wed Sep 13, 2017 4:59 pm

That is interesting. I have noticed a similar variance on our R31. Over the summer we did not use the furnace and we do not have a generator yet the fuel burn is about 5% off.

We were up in Desolation Sound as well and you are correct. Fuel is very expensive.

I am curious to see what others have to say about the fuel burn.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby Red Raven on Wed Sep 13, 2017 6:57 pm

Ours is a little less than 5% off the other way. It always takes a gallon or two less than I expect to fill it. I like it that way.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby Hydraulicjump on Wed Sep 13, 2017 10:52 pm

Thanks all. It really doesn't take much to adapt to this. Of all the things....

Webasto not used this summer, much to my thermally challenged spouse's delight. No generator. We are just off 5%.

There's a metaphor there, I am sure.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby knotflying on Thu Sep 14, 2017 6:25 am

As with Red Raven I always have to put a gallon or two less in when refilling and I attribute this to extra fuel in the fill and vent line. If you really want to feel better about the 5% difference, why not change your tank fuel capacity setting to 5% less. Who knows, maybe in reality the tank is slightly smaller ( or is that larger. To early in the morning to figure that out) than the capacity stated. The Garmin gives you the option of - fill tanks or - added quantity. If you are not filling up and just add a smaller quantity than filling up and the previous quantity existing was wrong, things will start to compound quickly. Also, you have a liters to gallons conversion when in Canada. I carried an excel sheet I made up with the conversion so I wouldn't make a math error on the fly.
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Re: Calibrate Garmin Fuel Flow Meter?

Postby Hydraulicjump on Thu Sep 14, 2017 8:45 am

Ha. Thanks Mike. The SIMPLEST solution of all is just to fill the tank every time. There are other benefits with this (reduce condensation and algae growth....although I follow your treatment regimen, so I doubt this would be an issue) and avoids the compound loss problem.

Jeff
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