Fuel gauge and consumption

[sjreib]

I have a 2016 Cutwater 28(100 gal fuel tank), about 70 engine hours. the fuel remaining reading on the Volvo Screen and garmin are usually identical or within one gal. Is the Garmin merely parroting the Volvo reading or is it based on actual consumption rather than the tank float sending unit. I've only done one fill up and the gauges both indicated I'd require 33 gals, but in fact the tank took 46 gals. Not very reassuring!
Any advice would be appreciated. Do I need to set the NMEA or is it preset on the Garmin??

 

[knotflying]

The Garmin measures fuel flow and is very accurate. However, you need to input proper information in the Garmin to remain accurate. I would suggest that you fill your tank and then set the Garmin to the full tank setting. Then every time thereafter when you get fuel you need to enter the amount of fuel added or if you fill the tank again just reset to full tank.
Reminder: The engine menu will not come up unless the ignition key is in the on position.

 

[randallmang]

My understanding is the Volvo gage is the true source of the data. The Garmin is just an interpretation and display of that data, in this case your fuel level.

 

[sjreib]

Still not understanding fuel consumption discrepancy problems. Although Garmin and Volvo(D4) readings nearly the same, I'm taking about 50% more fuel to fill up than the gauges would indicate I need. Read 32 to fill, took 45g. Read 45 to fill took 67g. This is on a 2016 C28, would love to hear back from anybody, but particularity 2016 Volvo D4 boats.
Thanks,

 

[knotflying]

Are you sure you have your tank capacity set correctly?

 

[sjreib]

Yes, but that's a consideration. The 2016 C28 comes standard with a 100gal tank. When I fill up, the Volvo display shows 100 gal.
Could they have mistakenly put an 80gal tank in, I doubt it but will double check that with the factory.
Thanks for the response

 

[Red Raven]

Sounds like the fuel flow sensor is inaccurate for some reason. I wonder if it can be calibrated?

 

[sjreib]

Maybe the fuel flow sensor is the problem-I'll check with the factory.
I'm still a bit confused though. Does the Garmin calculate fuel consumption independent of the float sensor in the fuel tank that the Volvo display shows or does it simply parrot the Volvo tank float sensor reading?
I've noticed the Garmin fuel display blinks until the Volvo ignition is turned on suggesting that they are tied together.

 

[Red Raven]

The fuel flow sensor is a separate system from the float gauge. It measures the fuel flow rate only. It does not know anything about the amount if fuel in the tank. That is why you need to set the tank capacity and reset the level each time you fill up. I'm not sure if it is available from the Volvo screens. I only use it from the Garmin screens. I don't often use the float gauge as it is dependent on the boat being level.

 

[knotflying]

Yes, but that's a consideration. The 2016 C28 comes standard with a 100gal tank. When I fill up, the Volvo display shows 100 gal.
Could they have mistakenly put an 80gal tank in, I doubt it but will double check that with the factory.
Thanks for the response

Well, If the tank installed is smaller, then you would have a reverse problem. You would not be able to get as much fuel in. As Red Raven said, the Garmin reads only fuel flow and then deducts it from the total tank capacity. So if the tank capacity was not set correctly initially, say 80 gallons, and you burned 20 the Garmin will show you need 20 gallons, but you will take 40 gallons. I believe the Volvo gauge works on the float and this can be inaccurate based on boat angle in the water and the fact that the tank is not of symmetrical shape. I would fill up the tank and then make sure you set the Garmin fuel tank capacity to 100 gallons. You have to have the ignition in the on position to get fuel tank readings on the Garmin. Each time you get fuel you have to either enter the amount of fuel you put in or if you filled the tank just press filled to capacity. The Garmin always deducts the flow used from the entered capacity in tank and then deducts for fuel remaining. I would suspect your issue is the initial tank capacity, but then again stranger things have happened.
Keep us informed on how things go.

 

[sjreib]

Thank you all for your input. Still not sure what the problem is as both the Garmin and Volvo read outs are erroneous. Each time I add fuel I always top off the tank and reset the Garmin to 100 gal. The Volvo gauge goes to 100 at the same time. So we'll call that a "good start"
I'm going to the rendezvous this week and will be watching the fuel gauges carefully and will have an opportunity to talk about this further with the folks who ought to know what's going on with these gauges.
Will post a F/U when I return with more information and an additional fuel fill up

 

[tlkenyon]

To make sure that the tank is actually full, I fill that last 5-10 gallons from a can at a very slow rate. When I confirm "full" I reset the Garmin to "full." Doing this, I have always come to within a gallon or so of what Garmin predicts I need to get a full tank. To reduce the mess from the burping that is inevitable (the tank, not me) I purchased a doodad that catches the burps (http://www.cleanwayfuelfill.com). I works pretty well and keeps the mess to a minimum.

I wished the tank accepted fuel at a faster rate so I would not have to use the can method. I have confirmed that the vent works, it is just that the fill hose is kinda long and has some bends in t before getting to the tank.

TK

 

[Scuffy]

We use a fuel whistle in line with the fuel tank's vent hose. They are available from Defender. Fueling, the whistle whistles and when the whistling stops you stop the pump. No spills anymore simple to install on your fuel vent line which I think was 3/4".

 

[Osprey]

When filling the boat fuel tank from a can, a "Shaker Siphon" (brand name) works very well. This siphon delivers about 3.5 gallons a minute. The Practical Sailor magazine rates this siphon highly.
As to the vent hose ID my recollection is 5/8 inch diameter not 3/4.
A poster above mentioned using a fuel whistle. My experience is that the whistle works fairly well as far as preventing spills goes. However, with foam up in the vent line, it tends stop sounding before the tank is actually full. Also the sound can be hard to hear when the fuel flow into the tank filler line is low. Still I am happy that I have the whistle installed, no spills during a couple of years use. West Marine web site has a video relating to this product. Use the WM search box with the search term 9396706 to get the full information.