Fuel mileage question

[oaksld]

I have a 1987 Proline 21' center console with a 2000 Johnson 175 ocean pro outboard.. earlier this year I filled the tank and it took 42 gallons.. I was told by my dad (who gave me the boat) that he thinks it is a 50 gallon tank.. I've never trusted the fuel gauge and the fill up confirmed that by only showing 3/4 of a tank.

I use a automotive gps for a speedometer and reset the trip odometer on it so I could get a decent idea of how far I could go on a tank.. I mostly make small runs out to some coves for some relaxing evenings.. The other evening it finally ran out and the gps said I had travelled 125 miles so my fuel milage was approx. 2.5 mpg.. I put 5 gals of gas in (I had been carrying it around in anticipation of running out).. the next day I set out (with another 5 gallons in reserve) and ran out after 12 miles confirming the 2.5 mpg

Does this gas mileage seem reasonable for a boat this size or do I need a tune up or something.. Motor runs fine but has a hard time idling.. sounds like it backfires through the carbs sometimes.

Thank you all in advance for your insight.. I love this forum and learn something new everyday!

 

[Mischief Managed]

Re: Fuel mileage question

Sounds about right, those carbureted 2 strokes get pretty bad mileage. If it had a 4 stroke OB you'd probably see 3.5 MPG, maybe better.

 

[Chris1956]

Re: Fuel mileage question

I have a similar boat and motor combo and see about the same mileage, when cruising at ~30 MPH. Be aware that boat load and water conditions can affect the mileage in a negative fashion. Try waterskiing for a couple of hours and see what that does to mileage, for example.

 

[bnicov]

Re: Fuel mileage question

That's probably about right. If it's not idling right, try changing the spark plugs to start with. You definitely need to keep a spare set on board along with a spare prop and the necessary tools. A tune up once a year is a must whether you do it yourself or pay a mechanic to do it. You can get a lot of help here with regards to that.

 

[dingbat]

Re: Fuel mileage question

I run a 22' W/A with a 200 Ocean Pro.

Cruise @ 4200 rpm (27 kts) / reasonably flat = 2.2 MPG. Add a 1' chop drops it back to 1.97 MPG, the usual 2’ chop kicks it down to around 1.5 MPG. Figures via fuel flow monitor

If it's not idling right, try changing the spark plugs to start with. You definitely need to keep a spare set on board

With 2500 hrs plus on my previous power head and almost 200 hours on this one, I’ve yet to foul a plug. I troll this motor 8-10 hours at a time at 800-900 RPM. Warm water, cold water, doesn’t matter. The right plugs, semi-synthetic oil and good fuel supply and no fouling whatsoever.

 

[oaksld]

Re: Fuel mileage question

Thanks for the info everybody.. makes me feel a little better knowing that it's normal fuel consumption... I replaced the plugs at the beginning of the season but I may go ahead and get another set just to keep on board,, I have a fuel flow meter but I quit using it because it said I was using fuel when the motor wasn't even running I'm going to break out the manual for it and see whats up with that!

 

[JoLin]

Re: Fuel mileage question

Yeah, you're right in the ballpark. I had a '86 Pro-Line WAC with a '96 175 Oceanrunner. I used 9-10 gph running in the mid-20's, too.

My .02