Calibrating Fuel Consumption on Garmin Unit

[Familyguy]

I own the 2017 23R and have been comparing fuel measurements between the Garmin and the Yamaha fuel gauge. I have come to the conclusion that the Garmin fuel calculations are considerably out and I would like to calibrate it, or bias it somehow to be more accurate. Any advice?
For the record the Yamaha fuel gauge is accurate while the Garmin shows fuel consumption at a much faster rate and therefore will show less fuel remaining than there actually is.
THX

 

[Salish Seaker]

That's funny because we have the opposite problem on our R23. The Yamaha gauge has never been accurate and the Garmin gauge has been pretty accurate since I add fuel every time I fill.

In any case, it's fairly easy to do. Check out Olygirl's Garmin Cheat Sheet download. Just search for "Garmin Cheat Sheet".

 

[knotflying]

That's funny because we have the opposite problem on our R23. The Yamaha gauge has never been accurate and the Garmin gauge has been pretty accurate since I add fuel every time I fill.

In any case, it's fairly easy to do. Check out Olygirl's Garmin Cheat Sheet download. Just search for "Garmin Cheat Sheet".

That cheat sheet only tells you how to set the fuel. I think the issue here is the consumption calibration. I have found mine to be very accurate on the Garmin. Are you sure you have set your initial fuel quantity correctly? It is important that you initially fill up the tank and have your tank capacity set properly. If you add fuel you need to add the quantity added at the time you put in the fuel to keep the information accurate. I usually fill up each time so I just hit the fill tank option. Less than filling up you add the quantity. If this does not work out for you you may want to talk to Garmin about possible causes.

 

[Familyguy]

Thanks for the input from all. To clarify, I always start from a FULL tank. I fill it up at the dock (the gas nozzle kicks off and YES I add it slowly at the end so the back pressure does not kick it off to early and the Garmin tank size is set to 80 gal). I then set the garmin to ‘Fill all tanks’ and at that point the garmin says that the total fuel on board is 80 gallons and the Yamaha also shows 10 bars- COMPLETLY FULL.
So far, twice I have travelled almost exactly 100 nautical miles (by Garmin) and then have filled up the tank. Amazingly each time I refueled the fuel taken on board has been exactly 40 gal (the literature on the R23 has advertised 200 nautical miles, so talk about truth in advertising!)
So when I have filled up both times the Garmin was saying that I had about 30 gallon remaining while the yamaha gauge indicated either 5 or six bars remaining( a little over 1/2 talk).
This is not a problem when running on the over 1/2 a tank however when I am heading home with 25 miles to go and Garmin is saying I have 17 gallons left while my Yamaha says I have about 34 gallons left it make me nervous.

 

[Navigator's Son]

I have a similar experience, and I have a suspicion.

I too am very diligent of watching exactly how much fuel I put in the tank. I hit Fill and start at 80 gallons. I keep a very close eye on the Garmin, run a steady 2550 rpm. The fuel flow meter says I burn 5.4 gallons/hour and average just about 2.25 nm / gal.

When I pull up to the fuel dock I can never add as much fuel as t the Garmin says I've consumed. The Garmin will say I have 20 gallons left. I should be able to add 60 gallons. Yet my tank burps at only 40 gallons added on the pump, and I struggle to even get to add 50.

What I suspect the issue to be is a design flaw in the gas tank air vent. I believe the fill/vent is at the rear most (stern) section of the fuel tank. When boat is new, it sits level, you can actually get all 80 gallons of fuel into the tank. But as you load gear on the boat, making the boat now stern heavy, you have created a barrier in the tank that pervents the air from escaping. The air gets trapped at the front (bow) of the tank and cannot escape.

I believe this is the reason the Garmin shows 30 gallons while your Volvo float shows 50 gallons.

Next time you go to fuel up, sink your bow ( that's the trick) and see how much fuel you can add now that the air can escape.

 

[Familyguy]

Sorry Don’t agree. The fuel used is correct, the distance travelled is correct,the fuel aboard as indicated by the yamaha fuel gauge is correct ( by the way that is a physical float in the fuel tank that appears to have been calibrated correctly at the Ranger factory-Good job Ranger folks!)
Garmin’s fuel gauge is based on a calculation given to it based on fuel consumption data which is provided to it by the Yamaha Fuel Management System (FMS). It is apparent that I am (and based on your own data so are you) getting better fuel mileage than Garmins interpretation of the data provided by Yamaha’s FMS thus Garmins calculation of the volume in the fuel tank is going down faster than actual fuel used.
A little background on myself,in addition to being an avid boater of 30 years, I’m an engineer at a refinery for 29 Years and have a deep understanding of how instrumentation works. The fuel gauge is accurate (1 bar equals about 8 gallons) but Garmins calculation of fuel used is not. Thus my original question ‘Does Garmin have the programming to allow me to give it a bias based on actual fuel used vs, theoretical’ So far my research says ‘NO’. So my next question (for Yamaha) is how do I, or can I, calibrate the FMS so that Garmin is getting the correct data?

I do appreciate your input as it also appears you are having the same issue which validates my own data.

YAMAHA and Ranger techs- can you help us?

 

[knotflying]

Garmin does have a GFS10 fuel sensor. perhaps if you can't get the Yamaha to talk nicely to the Garmin then this may be an alternative fix.

 

[BB marine]

Just something to think about. The fuel sender can be fairly accurate if it is calibrated right. Even if calibrated right while cruising it will be off considerably. The sending unit is in the aft section of the tank ( I would verify this ) After 2 years of second guessing which gauge is actually right. I recorded fuel from Garmin, Fuel from tank sender readings. Garmin recorded 31.5 gallons and The Volvo fuel gauge(sending unit recorded 57 gallons . I removed all fuel from the tank via fuel port on the tank.extracting it with a pickup tube and pump. I removed 45 gallons from the tank. The Garmin gets all of its information from you. It gets its data from the engine. The fuel gage gets its information from set up and calibrations and data from the sending unit. In my case I believe the data from the Garmin was correct and I may at one time entered incorrect information at an add fuel. Or the Garmin is off by approx 5%. I looked at total fuel used since purchasing the boat approx 700gallons the amount off was 13 gallons. Thats less then 2% inaccuracy over 700 gallons of fuel taken on board. The Fuel gauge set up from Cutwater/Ranger is a generic Full tank calibration. My gauge wasn't that accurate.

I also came from the petrochemical industry (Millwright) and installed Flow meters and level detectors working hand and hand with I&E technician. I used the method that was used similar methods to calibrate the gauge and sending unit on the bench and the calibrate the system in the boat to get a better accurate reading. The sending unit is similar to a mechanical/electrical level detector in a tank. I took resistance readings of the different segments of the sender to make accurate calibrations and take into account attitude of the boat to get it's accuracy closer to "real"




After recalibrating the sender and starting from an empty fuel tank with a known amount of fuel from the start my Garmin and fuel gage agree with in 3 to 4 gallons. The Garmin I feel is more accurate. It always shows slightly less then the Gauge. Your Garmin is getting its information from your engine fuel management, it should be accurate. I use the 5% rule ( I figure 5% less) I proved the accuracy to be less then that after 700gallons of fuel. but I add human error into that (Me). The picture shows the difference in the reading between the Garmin and fuel gauge/sending unit. The only time this has a large difference is in the first 15 gallons of use after filling the tank. I don't care about that because there is no reason to worry about fuel then. I want it to be accurate from 1/2tank to empty. I have those results now. This is a post that I started with a better description of calibration.viewtopic.php?f=18&t=10780#p74140. If none of this pertains to your issue I apologize for the long reply.

 

[Navigator's Son]

Let's start with a common acceptance that the Garmin is 100% accurate.

I tell my Garmin you have exactly 80 gallons capacity, and it's full. I cruised for a solid 7 hours - 70 nautical miles (Everett to Roche Harbor) and back with, therefore 14 hours and 140 nautical miles.

When I left Everett I actually started with just about 75 gallons of fuel on board (had taken the boat out for a short trip after topping off tank). When I got back to Everett the Garmin was telling me I had 13 gallons of fuel.

For the life of me - I was lucky to put 50 gallons of fuel into the tank. I maybe pushed 55 gallons. That's only 68 gallons. Why can't I get that last 12 gallons back into my tank?

 

[Familyguy]

Brian I agree with your methodology and data you have provided but My boat has the Yamaha and yours is the Volvo. What I’ve learned from you is that the fuel consumption data that Volvo is sending to the Garmin is more accurate. 😀

For Navigators Son: Exactly!
Calculating 140 Nautical miles @ 40 gal/100 = 56 gallons you should have burned (Based on fuel consumption specs given by Ranger) which is exactly what you put in. In reality you still had 24 gallons left. :geek:

 

[mseca]

Can you please explain to me how to get to the add fuel pare to my Garmin, I just bough my 2009 25 RT
Thanks Mike

 

[Navigator's Son]

Can you please explain to me how to get to the add fuel pare to my Garmin, I just bough my 2009 25 RT
Thanks Mike

Mike, you have to start from your Fuel screen. At the bottom of screen you should see I believe it's "Menu" or "Edit" - it's just to the right of the "Home" tab. From menu you then should see a list of options on the right, "Fill Tank", "Ad Fuel"...

When you select Add Fuel, you need to enter the leading 0's. For example 00020 to add 20 gallons.

 

[BB marine]

download/file.php?id=659

This is a cheat sheet for the 7612. I'm not sure of what unit you have and if it is connected with N2K. Also if the engine on board, Yanmar, Cumins, has fuel flow calculations in the electronics. If so and the Garmin set up in your Tug is the same as the Garmin that this topic is talking about use the cheat sheet attached.

 

[Matty]

When doing this analysis you want to eliminate as many unknowns and estimates as possible. Personnally i would never use the"fill all tanks". Due to air pockets and leveling issues it is not accurate. But if you pay for 60 gallons you can bet that is accurate. One guess is eliminated. Secondly, using any fuel data supplied by manufacturer is another inaccurate number. Weight on vessel, acceleration habits and cleanliness of bottom throw all this data out the window. With a clean bottom i get 30% better fuel economy.

 

[knotflying]

When doing this analysis you want to eliminate as many unknowns and estimates as possible. Personnally i would never use the"fill all tanks". Due to air pockets and leveling issues it is not accurate. But if you pay for 60 gallons you can bet that is accurate. One guess is eliminated. Secondly, using any fuel data supplied by manufacturer is another inaccurate number. Weight on vessel, acceleration habits and cleanliness of bottom throw all this data out the window. With a clean bottom i get 30% better fuel economy.

Here is my twist on your assumption not to use "fill tanks" : I always see what "fuel remaining" shows on the screen and compare that to what I actually put in. There is consistently about a gallon less fuel put in each time I get fuel. I fill that sucker pretty much to the top since I have a vent whistle. I assume that the 1 gallon difference is the additional fuel in the lines. If one was to only "add" what the pump says then eventually your actual and fuel remaining will be off by (using my observation) one gallon each time. Agreed, there may be times that air is trapped or other conditions may make "fill tanks" inaccurate, but at some point that will change to be correct when the moons align.

 

[Matty]

While I don't quite understand why that happens at least you are able to verify and be within a gallon. That is a lot less variance than some of the other experiences on here so sounds like you are using a reasonable test and have good accuracy. I recently "filled up" and it took less than I thought it should. I am going to add using 5 gallons cans and see how much more it takes as a check.

 

[BB marine]

While I don't quite understand why that happens at least you are able to verify and be within a gallon. That is a lot less variance than some of the other experiences on here so sounds like you are using a reasonable test and have good accuracy. I recently "filled up" and it took less than I thought it should. I am going to add using 5 gallons cans and see how much more it takes as a check.

As Mike has said it comes out in the end.I can't speak for others but when it comes to filling the boat it is a process. If I am trying to fill it all the way. Normal boating I give up and rely more on the fuel gauge but still hit fill tank on the Garmin. But if I am traveling and want to start the day with a true full tank it takes a while. The Clean Way Fuel fill helps with spills but not with speed of filling. I normally use my Garmin reading and fuel gauge. The Volvo gauge now that it is calibrated is slightly more accurate then the Garmin from 3/4 tank to 1/8 th of a tank. Garmin is off by about 5%. Between the Garmin reading fuel gauge and estimated GPH based on rpm that I am running I know how much its going to take to fill it. If it is a fast pump I usually tell the Gas dock attendant " this is going to take a while, I always fill myself. It does come within a gallon or 2 of the three combined readings, mine ,fuel gauge, Garmin.I used to it now and comfortable with knowing how much fuel I have.

 

[knotflying]

The reality is no one should be letting their fuel get so low that a super accurate amount remaining is critical. Having a 100 gallon tank I have never gone below 30 gallons.

 

[Matty]

fully agree. I have 150 gallon tank and most of the time operate in the 50-90 range when taking day trips so as not haul extra weight around. If going on a longer trip I would of course fill it up.