Gas gauge accuracy

[stinson]

Hi Guys,

I returned to the dock yesterday with 3% fuel (measured at rest by my Garman). I would normally never let it get that low but was trying to run the tank down due to end of season here in the north. I was sweating it out thinking I was going to run out of fuel. Any idea as to the accuracy of the fuel gauge in my 2019 R23?

 

[Craigmconrad]

I will be interested in knowing also. What does the remaining fuel show in gallons? My last fill up showed 36 gallons remaining and I put 56 gallons in to top it off. It's only a 80 gallon tank, so my Garmin was off by 12 gallons.

 

[CruisingElvinRay]

We cruised into Coinjock, NC with one bar left, and that bar was flashing (burned a lot of fuel crossing Albemarle Sound) for about the last 10 miles. Was very concerned we would not make it.

Topped off at Coinjock, and she took 72.8 gallons.


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[stinson]

I noticed the reported fuel was higher while cruising than at rest. This would imply the level sensor was at the back of the tank, hopefully where the fuel pickup is as well. So in desperate times it may be best to have the boat bow up a bit rather than flat. I would imagine two gallons spread out over the entire tank is just about zero.

 

[Maggie Anne]

I find the Garmin fuel on board readings to be pretty accurate although it will need to be reset occasionally. On my recent trip to Alaska this summer in my R27OB, I burned about 1600 gallons of gas to go up to Glacier Bay and back. At the beginning of the trip and at each fuel stop I refueled to the max as determined by seeing the fuel level a few inches below the cap in the filler tube. The reported fuel used by my Garmin was always close to the amount I was able to put into the tank, although the Garmin indicated a little more fuel used than it actually took to refill the tank. At the beginning of the trip I set the fuel on board to the tank capacity, 150 gallons. During the trip I never reset the amount of fuel to 150 gallons but instead just used the "Add Fuel to Boat" option and recorded the actual amount put in each time. At the end of the trip, I refilled the tank and the fuel on board read 134 gallons, even though the fuel level in the filler tube was again right up to a few inches below the cap. So, over 1600 gallons, the Garmin overstated the fuel burned by 16 gallons, (150 minus 134), or 1% of the total burned during the trip.

I also found the MPG reading on the Garmin to be quite variable even at constant RPM and speed. I found it better to take the GPH from the Yamaha display (or from the Garmin) which was fairly stable at a constant RPM and divide that into the MPH to get MPG.

 

[Submariner]

If you’ve got the kicker, it’s fuel consumption bypasses the engine stats and thus doesn’t get reported to the Garmin at all.

At wot, the 9.9 kicker will use 1gph per the service manual.

My Garmin is usually within a gallon of accuracy for what I need to put in, vs what the pump says I put in. Unless I put hours on the kicker. Then it’s usually a couple gallons off, understandably, based on my usage.


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[rpmerrill]

Do you store your boat for the winter with an empty tank?

 

[Someday*]

Does what the generator uses get "measured" by the Garmin?

 

[knotflying]

My experience has been that the Garmin is very accurate. However, It is important to accurately reflect fuel entered each time in the fuel added menu. The most accurate is to first set the tank capacity. If filling up to capacity you just have to hit the "fill tanks" option. This will give you the most accurate reading long term. Think about the math, if each time you put in fuel to the brim with a 150 Gallon tank your capacity is slightly more because of what is in the hose from the tank top to your fill cap. The Garmin is doing the math based on a 150 gallon tank and then deducting the fuel consumption. The Yamaha gauge is a basic float that interpolates gallons in tank based on ohms. Depending on angle of boat this can be very different from reality. My practice is to rely on the Garmin info and use the fuel burned info from the Yamaha gauge and manually do the math to compare both. You will discover that the Garmin and the math will jive. You do have to also reset the fuel used to zero on the Yamaha to get an accurate reading after you fill up with fuel. One should never really run out of fuel if you make it a custom to never go below 2/3 empty and then fill her up.

 

[BB marine]

There are two answers given to one question. (1) How accurate is the Gas gauge? (2)How accurate is the Garmin if all information is entered correctly starting with a full tank and ending with a full tank and entering the correct gallons at each fill up.

Both answers need to be answered with conditions.

The answer to. the question how accurate is the fuel Gauge. This is the Yamaha gauge that is getting the information from the fuel tank sender. The sender is a KUS SSS/SSL 5 hole that uses reed switch and magnetic field technology. The only moving part is the float. This sending unit if PROPERLY CALIBRATED to the Yamaha fuel gauge is very accurate especially when the tank is 1/2 full or lower. It uses a resistance range of 240 ohms to 33 ohms. 240 is empty and 33 is full or 100% empty depending on the gauge program. There are different resistance readings from the empty 240 ohms lower most part to the highest part. Each resistance change is programed into the electronic Yamaha gauge in fuel tank percentage. The information of tank capacity is entered when calibrating the fuel gauge and the Yamahas gauge's program does the calibrating of fuel in gallons from percentage of fuel in tank. If the sending unit is calibrated accurately the fuel gauge is very accurate. I found with 0 to +/- 3 gallons used on a 80 gallon tank. Now the important thing to know is the sending unit is not calibrated this way from the factory. It is calibrated in a on step 100% full calibration which does not take into consideration the irregularity of the tank dimensions and the fact that the sending unit is off the bottom of the tank 1". This can change the accuracy by 10 to 20%. So not very accurate! If you want to have an accurate gauge calibrate it.


viewtopic.php?f=18&t=10780&hilit=+calibrating This calibrating a EVC Volvo gauge. The Yamaha can be done similar. It takes a some time to calculate the resistances or percentages to the tank. It would be an awesome addition to Fluid Motions check sheet to add calibrate the fuel senders to accurately match the fuel tank level. Disregaurading a fuel tank gauge and saying it is not accurate use the Garmin because it is more accurate is not acceptable to me when purchasing a quality built boat.

Using the Garmin is a great resource but it relies on input information. You MUST have a KNOWN about of fuel and enter the information ACCURATELY each time the fuel tank is filled and keep a log to confirm your fuel burns and you can be with in 0 to 5% of accuracy. If you miss one or two times of this or guess at one or two times the Accuracy is out the window. Redundancy is alway the safest method. Use the Garmin and have a accurate fuel gauge to rely on. This is not the 90's when we bent a sending unit float to set the fuel gauge to be accurate enough to know when the tank is low. The electronic gauges and floats made today are acute as long as they are calibrated properly.

This is photo showing the Garmin information ( I always enter the information at each fill up) and the Volvo EVC using the KUS sending unit calibrated properly. They agree within a gallon. This photo was taken when I was leaving a marina and set to cruise to my next destination I was at idle and confirming my fuel on board. When I filled up my tank I always used the Volvo gauge as my go to I found it to be slightly more accurate then the Garmin. This was after calibration. Before calibration it was off considerably and unreliable.gallery2.php?g2_itemId=65368