Mpg

[Butch54]

I have a 1977 SRVHT, 233hp. Wonder what kind of MPG I should be getting? My gas gage wont go lower than 1/4 and no higher than 3/4 so I don't think it is working correctly. Probably a problem in the sending unit in the tank. Anyway would like to know about what I should be averaging for MPG. Thanks....

 

[Hampton]

How much does it weigh? I assume it's carbeurated. What kind of drive. More details about the boat would help decide. Normally people talk about gallons per hour, but on a steady cruise in calm waters, mpg can help alot too.

1997 250Da with 5.7 fuel injected - 2.5 mpg at 25 mph (235 HP)
2005 340Da with 2 8.1 fuel inj - .85 mpg (heavy) at 25 mph (740 HP)

 

[Butch54]

Sorry about the typo John, I did mean MPG. My Hard Top is about 4,000 lb empty. Yes, its has a carb and the sterndrive is a 1.47 gear, Alpha . I know that on plane, about 22 mpr, the MPG is better but most of the time I just cruse around 10mph. The gas gauge works but not reading correctly within "Full" to "Empty". The tank is 75gal full. The reason I ask is that some day, after I get the gauge fixed, I want to put it in at Chicago and go down to Peoria Illinois. So I was just trying to get an idea about the gas consumption.

 

[Hampton]

Sounds like you will burn around 10 - 12 gph at cruise, for about 2 - 2.5 mpg, if you are tuned up and the bottom is clean (maybe even a little better economy). The mpg of a boat is at the highest just above idle. 10 mph may be pretty inefficient. If you are making a pretty good wake, but not on plane, you're not very efficient.

If you can picture a graph to represent mpg versus speed (speed increasing from zero on left to max on right), it starts in the middle and goes up to max economy at some speed generally around 6 or 7 mph, then begins to decrease as you start to move more water, but don't speed up much (plowing). As you continue to increase speed and power, the economy reaches a low point and then begins to rise again until you reach a minimum, but comfortable, plane speed. This is your max economy at cruise (generally). It will be a little lower than your economy just above idle. As you continue to increase speed, economy is generally fairly flat for a period and then drops at an increasing rate as you reach max speed at which point the curve ends.

 

[helms1200]

Hi Butch, the fuel gauge on my boat would not move much at all. I pulled the sending unit from the top of the tank it was rusted. sprayed it with wd-40. worked it around a little. now it works great.

 

[Butch54]

Thanks Hampton, that gives me some kind of an idea given all the variables.

Helms, I can do some electric work my self but I feel uneasy working with the gas gauge or sending unit. I think I will leave it to a mechanic to do so I know its done right and safe. I am big on safety, ask anyone that rides with me. Thanks.

 

[Butch54]

Found the sending unit

Helms1200, I found the sending unit hiding under the floor and new carpet. Going to give your idea a try. Thanks…..

 

[Lazy Daze]

As was mentioned, those resistors can get fouled up over time. If cleaning it doesn't help (as a last resort, try one of those green, scrub pads), you can get a replacement unit just about anywhere for about $30. Tempo is probably the brand you'll fine.

While you play with the arm, keep your gauges activated and the sender plugged in. Watch you fuel gauge. See if it gets any better before you go and screw it back in.

 

[Butch54]

Fixed it!

My gas gauge problem is solved. I removed the sending unit to find that the limit tabs were stopping the full movement of the gauge. I set the Empty limit tabs so the gauge read Empty to Full, but when I get the tank down to almost empty I will check it again. I would like a few gallons of gas still in the tank although the gauge reads Empty.


Thanks to everyone again for all the ideas and tips to solve this. I am glad I can be part of a group of everyday boaters that help out. I hope I can do the same….:smt038

 

[Lazy Daze]

Gotta love those repairs that cost $0! Glad you got it figured out.

 

[brains06]

Hey...I have the same issue with my fuel gauge not reading correctly. How did you know what was what and where to find it? Mine reads full but once it gets past 1/2 tank its anyones guess...plus it doesnt go all the way to E. Empty is between E and 1/4. I've only gotten it down that low once.....and thats when I learned of the issue.

 

[helms1200]

Hey Butch. Nothing like the feeling of fixing it yourself! And Jason, my sending unit was under the hatch on top of the tank with two wires and about six or eight screws holding it down. Just remember where the wires go and the direction the float is so when you put it back in it works properly with out hiting the side of the tank. Its a pretty simple job to do.