Df175 wrong fuel flow?

[caltexvb]

Have a Df175 hooked up to a Garmin GMI 20 to indicate fuel quantity and consumption. The other day I ran out of fuel even though the GMI 20 was indicating 90L of fuel on board. I've since made up a dipstick to take a direct reading from the tank and after 2 subsequent trips it would appear that the engine is using more fuel than is being recorded by the GMI 20.

Is there anyway that the fuel flow indicated on the GMI 20 could be wrong or has anyone experienced incorrect fuel consuption with this type of set up?

Thanks!

[Moonlighter]

1. How long have you had the NMEA2000 system set up? Has it been accurate before this latest problem?

2. have you ever before compared the actual fuel used when you filled the tank with what the Garmin said? That is the only accurate way to know whether the system needs to be calibrated or not.

Need to know some more info before we can advise you correctly, so please answer the above questions first.

[caltexvb]

Thanks for the quick reply. The boat is only 4 months old so it's all a bit new to me as my previous boat had analogue gauges. The NMEA 2000 network has been installed since new. I wasn't even aware there was a problem until I ran out of fuel and assumed until that point everything was reading correctly.

The boat has a 260L tank so never fill the tanks to full as I don't use this much per trip and don't want fuel going stale sitting in the tank or having to tow the extra weight around. Due to this I have never become aware of the discrepancy in fuel consuption.

I have also just discovered that the lowrance sounder in my boat also hooked into the network is showing more fuel used than the GMI 20....

[Moonlighter]

Ok, it is good to know the full picture of what you have got on your network, both the GmI and the HDS. Is there anything else apart from them and the Suzuki attached to the network?

I note you're using litres, so assume you're not in the USA? Aussie? Located where? With a user name "Caltexvb" I would guess you are an Aussie from Victoria, that's the only place I know where anyone drinks that VB beer!

It is possible that the is a conflict between the Lowrance/Suzuki and the Garmin. Seen a couple of cases where that has happened.

What you may not know is that Lowrance makes the Suzuki engine interface and the interface can only be configured by the Lowrance unit. The Suzuki interface has an in-built memory/data storage module in it and this is where the fuel used and related data that is calculated by the Lowrance HDS is stored.

The problem is that the Garmin also has an inbuilt storage module in it.

So sometimes things get confused and you get different results on one unit to the other. Especially if you use the Garmin unit to do the refuel process but don't have the Lowrance turned on when you do it.

So, here is what I would ask you to do.

Go into the Garmin menu and find the network menu, and find the data sources listing.

The data source settings tell the GMI where to look on the network to find fuel used/fuel remaining info. It will probably be set to itself. See if you can change it to look at the Suzuki interface for fuel used etc. if you do that, it should then change the litres of fuel left to be the same as what the Lowrance says.

If that works, the next step is to refill the boat to full, do some trips and use at least 50-80 litres, the more the better, and then fill up again and compare actual with predicted.

This is the ONLY was to know for sure if your system is under-calculating and needs to be calibrated. Try to get the fuel from the same bowser at the same fuel station so the tank is sitting at the same angle and fills as closely as possible to the same level each time.

Now, if you refill the tank and it takes 80 litres, but the Garmin and Lowrance both say 73, then, go into the Lowrance menu, find the refuel menu, and select fill the tank. Make sure the key is turned on when you do this.

It will then give you an option to calibrate, say yes, and then it will want you to input the actual amount added. Do that, and complete the process. What that does is to adjust the calculations and next time you fill up, it will be closer to matching 100%. You can only do this calibration process in the Lowrance, the Garmin can't do it!

You might need to repeat this process a couple of times before you get it 100% accurate.

As a further note, one of the problems with continually doing partial fills like you've been doing, where you never fill the tank up, is that you will miss any little inaccuracies. So eventually, you will run out of fuel, exactly as you experienced.

I do understand your rationale for not filling the tank, but to be honest, the info from the fuel companies tells us that a half-full tank of unleaded goes off much faster than a full tank. Plus you lose more from evaporation. Plus, you run a far greater risk of getting condensation in the tank and thus water in your fuel.

For those reasons, all my mates and I always keep our tanks full. We fill up on the way home most of the time.

A while ago I was having some work done on my house so didn't use the boat for 4 months. I had left it with 40 litres in the 100 L tank because prices were ridiculously high that weekend and I intended to fill it up at the low point in the price cycle.

When I eventually got the boat out and filled up on the way to the boat ramp, it took about 66 litres to fill my 100 litre tank, so I lost around 6 litres in 4 months due to evaporation.

So you can see that your practice of keeping the tank only partly filled could easily contribute to you having quite a bit less fuel than you think. If I had just added 60 litres, I would have been 6 litres short. Do that 5 or 6 times, a bit more evaporation each time between fills, and it soon adds up. In your larger tank it would lose even more.

Anyway, make the changes suggested and let me know how you go. We may have to mess about with this a bit to get you sorted out, but we will get it sorted one way or another.

Cheers

Grant

[caltexvb]

Thanks Grant. Your comments re my user name are spot on. Live in Perth but currently on a fishing trip at Exmouth. Heading out fishing tomorrow and will report back. Thanks again.

[caltexvb]

Unable to find a source option on the GMI 20.

[Moonlighter]

Refer page 6 of the quick start guide. I am not all that familiar with the Garmin menus. But it looks like you can select sources from the instructions on P 6.

Meanwhile, I'd suggest you rely on the Lowrance fuel data rather than the Garmin!

I will drop past my local Suzuki guy this morning and have a chat to him about this and see if he has ideas. One possibility is that the GMI might need a software update, I had heard something about some issues relating to fuel flow that they were having and people were waiting for the SW update to be released.

Have your GMIs ever done any "freezing up" on you? That was one of the problems causing inaccurate fuel used results. I have just googled and found several reports on Ausfish from mid to late 2014 where this was happening and people running out of fuel when gauges said 70-80 litres still left. Sounds very similar to what happened to you!

In any case, check the SW version your GMI is running and compare to latest version on Garmin website, and update if it's not the latest.

[caltexvb]

Thanks Grant. The manual you may be referring to off the website is for a GMI 10 (strange that it appears as support documents for the GMI 20) and I am unable to find anything in my quick start guide about change sources other than for speed.

As for a software update, it would appear one was released just last month but will have to by an SD card reader to upload it to the device.