fuel gauge

[chaz]

I'm look to buy a smart fuel gauge the ones that tell to the gph while you are running. Can someone make a recomendation. Reason being I thought I had a 100 gallon fuel tank (1978 scepter) My gauge was flashing on empty (2000)225 HP Yammha)and I only took 75 gallons. I'm confused should my gauge be flashing on empty when I have 25 gallons left in the tank ? any thoughts on this

[MasterBaiter]

I'm look to buy a smart fuel gauge the ones that tell to the gph while you are running. Can someone make a recomendation. Reason being I thought I had a 100 gallon fuel tank (1978 scepter) My gauge was flashing on empty (2000)225 HP Yammha)and I only took 75 gallons. I'm confused should my gauge be flashing on empty when I have 25 gallons left in the tank ? any thoughts on this

I have the Faria Fuel Monitor. It seems to be a great thing. Easy to install and keeps track of more fuel things than I care about. I use it in addition to my fuel gauge.

As far as your fuel gauge, if it is not the first time you ran the tank to that level I would say the sender is dirty. My understanding is the sender runs on resistance. If it became dirty there would be more resistance and bad readings. Alcohol in the fuel might be the cause of moisture and corrosion on the sending unit.

[wavelength]

What tpye of electronics do you have?? I have the LMF-200 Multi-Function Gauge from Lowrance but there is a catch. I put the first one on in 05 when I got the boat and have replaced it twice under warranty, the third time in August.

I have a X-15MT plotter that does not support the newer LowranceNet so my fuel flow was suported by a paddle wheel for speed input giving me miles per gallon.

In Aug the one they sent was a 2009 unit that ONLY gets speed from a newer paddle wheel or the network. So now have no speed input but it does still give me all the info on fuel used, gallons per hour etc.

My point is the LMF-200 is a multifuntction gauge that does much more than my X-15MT plotter can support.

It is depressing to see that my 1989 225hp Johnson is burning 13.5 to 15 gallons per hour making 24 to 27 knots!

[bj]

I had 1977 Sceptre and if my memory is corect it had an 85 gal tank with around 72 or so useable gallons. It was an I/O so the tank may have been smaller than the outboard version. Those gauges are so inaccurate though it could easily read empty and still have 25 gals in it. If you run it down that low quite often it would be smart to install a fuel monitoring system so you will know exactly how much you have burned.

[McGillicuddy]

Sometimes replacement fuel gauge sensors are too long or short for the actual tank depth, put in at a poor angles, or simply get stuck. I have never had a fuel sending unit sensor that I really trusted. I don't know if people really take the time to calibrate them. They tend to pop them in and if they give a reading, they are assumed to be fine

Currently I have an inline Navman/Northstar fuel meter unit that gives me all kinds of info including gallons burned, remaining, low fuel alarm, mpg, gph, fuel consumption curves and assorted other things I don't use. Probably not nearly the quality of a Flo-Scan but it works and is pretty accurate. It can be calibrated and it's also smartcraft compatible should you opt to re-power with a modern fuel-efficient Mercury motor.

The catch is you must always reset your fuel level upon refill as it is just a flow meter with no inside tank sensors...

My actual fuel gauge has a sensor but when over flowing at the vent, it insists that I only have 3/4 of a tank, also because of the quasi-hex-parallelogram shape of the Seafari tank it cant be nearly as accurate as the inline unit which also has the advantage of being situated between fuel/water separator and carb keeping it much cleaner than if in the tank.

[Bushwacker]

You MAY only have a 75 gallon tank! That happened to a friend of mine with a Sceptre on one Bahama trip! He gets to the gas dock with gage on empty, and, thinking he has a 100 gallon tank, dumps 2 gallons of oil in the tank before refueling. (This was 25-30 years ago when we all ran 50:1 premix). Tank overflowed at 75 gallons! A big blue cloud followed him around for the rest of the trip!

Floscan is the best flowmeter. A little pricey but aerospace quality and top notch customer support. We used their stuff in testing jet engines when I did R&D work at Pratt & Whitney. I installed one on my boat about 25 years ago and I could predict how much gas it would take within about 0.2 gallons!

An even better option, if your engine is fuel injected, is to just use the factory system that ties into engine computer. The BRP I-Command system I have, similar to Merc's Smartcraft system, gets fuel flow from the computer and uses speed from a GPS antenna to calculate all sorts of stuff . . . instantaneous MPG (VERY handy for setting optimum cruise speed, trimming engine and tabs, etc.), fuel burned, fuel remaining, range on existing fuel. I was a little skeptical of the accuracy of the CALCULATED fuel flow, but took a long trip down the St. John's River last spring and when I refueled, the Floscan measured fuel burn matched the calculated fuel burn and actual fuel used within 0.1 gallons! The photocell finally died in the Floscan and it's so old that they don't stock that part anymore, but factory said I might be able to find one on the internet. No big deal as I'm now in a believer in the I-Command system!

It's also possible to calibrate the gas gage, which I did when I first got the boat. Make sure boat is level or at least at the same attitude as when in the water, and hook up battery charger so voltage level is same as when engine is running, as that will affect gage reading. Gas gage is essentially a voltmeter that reads voltage drop across the resistor in the sending unit. I put some white vinyl tape across face of gage, drained tank, refilled from 6 gallon cans, and put a tick mark on the tape adjacent to the needle after every 6 gallons. It worked pretty well and I could predict how much fuel it would take within 2-3 gallons.

If you don't calibrate the gage, I agree with Gillie . . . about the only thing you know for sure with a gas gage, if needle is moving, that there is SOME gas in the tank! If needle doesn't move, you don't know anything!
Denny

[Fr. Frank]

Let me begin by making a statement: SeaTow and TowBoatUS make a great deal of money off people who don't monitor their fuel flow and instead depend upon their (often faulty) fuel gauges. Similarly, as a Civil Air Patrol/US Air Force Auxiliary captain I can tell you that fuel exhaustion causes a great many aircraft to stop flying unexpectedly, often with fatal results. Far too often the cause is pilot error, i.e.; the pilot just looked at his gauges and payed no attention to fuel flow in comparison with flight duration.

You need to know your actual useable fuel capacity and your fuel burn rates at a variety of speed/power settings.

My 1972 20' SeaCraft Seafari came equipped with what the SeaCraft sales brochure said was a 30 gallon fuel tank. Even after running the tank "dry", I was never able to get more than 27.4 gallons of gas and 1/2 gallon of oil into the tank, for a net 27.9 gallons usable fuel.

When I replaced the tank with a new one made using the old tank as the template, it held 27.2 gallons of pre-mixed fuel when I filled it up for the second time. My new tank was labeled by the manufacturer, RDS, as having 27 gallons capacity, even though it held 30.3 gallons on its initial fill up. When I asked about the difference, they indicated that they are in the process of beginning to label their marine tanks with the usable capacity to avoid confusion.

At any rate, I know my best fuel burn and my average fuel burn, not from a Navman, but from doing the following:

Buy a 6 gallon portable tank or two. Run your boat in normal safe operation, (including normal repeated acceleration) to see how long it takes to exhaust the 6 gallons. Refill the tank and do it twice more. Then refill and run at cruise speed and WOT (or 95% power minimum) and calculate fuel burn at those settings.

Know your fuel burn. It might save your life, and the lives of people you care for.

When I bought my 1970 20SF it had a Flo-Scan system on it and no actual fuel gauge. I was not happy because I could not see "how much fuel was left". I have been using it now fro several months and I have come to realize that the fuel gauge is not necessary. I know how much fuel my tank holds - all the way to empty - and I simply watch the fuel used on my flow meter. It has been accurate to within 1/2 gallon when I fill the tank up after a trip.and measure. I love it!