CONTINUOUSWAVE

I have [a Moeller 22-gallon on-deck fuel] tank on my 2003 170 MONTAUK. [The fuel tank level gauge] never seems to read full, even though I am certain [level of fuel in the] tank is [full].

Q1: Does [a replacement tank cap with an integral fuel tank level gauge made by KELCH as part #7J203085 with a 12-1/4-inch float depth] actually work [that is, will the tank level indicated be accurate]?

[I am asking because] I do not think there is any possible way [the boat is] getting only 2 to 3-MPG at 3500 to 4000 RPM with a brand new Yamaha F90 VMAX.

[Moderator's note: Separated from a nine-year-old thread that was revived.]

I have the same tank and use a simple wooden dowel to check the level when it's low. This only works in calmer water but it's simple and cheap.

For some further context, see the article

The MOELLER 24-gallon White On-deck Fuel Tank for Boston Whaler Boats
https://continuouswave.com/forum/viewto ... 154#p33778

The KELCH company manufacturers many fuel tank caps with integral tank level gauges. To make the best selection of a replacement cap, I suggest it will be prudent to contact the company for advice on which particular current product is the best choice for re-fitting onto the Moeller 22-gallon plastic fuel tank.

For example, the current product that might be better could be their 225--series Cap/Gauge. See

https://kelch.com/products/caps-gauges- ... -capgauge/

RaySmiley wrote:...I do not think there is any possible way [the 170 MONTAUK boat is] getting only 2 to 3-MPG at 3500 to 4000 RPM with a brand new Yamaha F90 VMAX.

If you are depending on a fuel tank level gauge to deduce the fuel economy of the engine, you might not be approaching this in the best way. Almost all modern outboard engines with a NMEA-2000 interface will be sending data on their instantaneous fuel flow rate. And almost all modern NMEA-2000 displays or dedicated gauges can receive this instantaneous fuel flow rate and, if an accurate boat speed is available (typically from a GNSS receiver) can compute the instantaneous Miles-per-Gallon fuel economy. In addition, modern displays and gauges can deduce the total volume of fuel consumed over a particular period of engine operation and also log the total distance traveled, and with that data compute an average MPG for the longer period.

Even without these modern engines, a NMEA-2000 network, digital data, and instrumentation that can perform calculations, you can probably better track fuel consumption by the old-fashioned method: fill the fuel tank to full, using some repeatable mark or indication, operate the boat, record the distance traveled, and then refill the tank to that same full level. Use the volume indicated on the pump that dispensed the fuel as the volume of fuel consumed. This method will be likely to produce more accurate fuel consumption volume than relying on a rather low-resolution tank level gauge as the means of measuring the volume of fuel in a fuel tank.