Dissappointed with gas mileage, any advice?

[JJ Bones]

I have a 1991 Thunderbolt bassboat (17'8") which weighs about 1180lbs. dry with a 1991 Johnson V-6 150 horsepower. I have a 20 gallon gas tank and it only lasts about 15 miles (estimate). Granted, I like to generally drive fast, rpm @ 6,000 (or at least that what the meter says). I have a jackplate and stingray foil attached. I recently had the motor tuned-up which included a carb cleaning. Could this be right or it there something I can do to increase range? Do some of you bring extra gas along in a portable tank? Any ideas or suggestions would be appreciated.

 

[JRJ]

Re: Dissappointed with gas mileage, any advice?

A 4000 rpm cruise will help properly trimmed. A 150 4stroke or EFI 2stroke will really increase your milage. Maybe tow a fuel barge? Good luck and welcome to iboats

 

[Dhadley]

Re: Dissappointed with gas mileage, any advice?

Welcome!!<br /><br />Which 1991 150 do you have? The crossflow or the 60 degree looper?

 

[Chris1956]

Re: Dissappointed with gas mileage, any advice?

JJ, You have four choices (or combinations of these). <br /><br />Use a higher pitched prop, if it will still allow you to get into WOT range.<br /><br />Make sure the Stingray is out of the water when you are on plane, so it doesn't drag, or remove it.<br /><br />Trim boat to achieve max speed.<br /><br />Back off just a bit (10%) from WOT. You will go nearly as fast, but save a lot of fuel.<br /><br />Failing these, get a bigger gas tank and another credit card.

 

[Mischief Managed]

Re: Dissappointed with gas mileage, any advice?

There is something seriously wrong of you can only get <1 MPG with 150 HP driving a 1200 lb boat. I'd find out where the gas is going cause it's not making HP.

 

[QC]

Re: Dissappointed with gas mileage, any advice?

I'm with MM.

 

[JJ Bones]

Re: Dissappointed with gas mileage, any advice?

The motor is the crossflow ... the prop is stainless with four blades ( I,m not sure exactly what size or pitch it is). What is WOT? I do not have a trim gauge ... how do you know when you trimmed up too high? I am definitely going to take the stringray foil off and try without.

 

[navigator336]

Re: Dissappointed with gas mileage, any advice?

You definitely don't need the Stringray foil with that engine and boat weight. WOT = wide open throttle. The engine manual whould state what RPM's should be reached at WOT. If you are getting less, use a lower pitch prop. If you are able to exceed the recommended WOT go to a higher pitch prop. Trim is generally optimal (on relatively calm waters) just before the boat starts to porpoise (the bow is going up and down).

 

[QC]

Re: Dissappointed with gas mileage, any advice?

navigator's advice is correct although I will add that if the boat is bow heavy, the RPM may start rising rapidly at high trim and speed levels before she will porpoise. You'll know when this happens . . .

 

[jlinder]

Re: Dissappointed with gas mileage, any advice?

I don't know what the WOT (wide open throttle) should be, but 6000 RPM for an I/O with a 6 cyl. engine sounds awful high. What would redline be for this engine?<br /><br />I find maximum economy occurs just after the boat gets on plane. After that I get more speed, but sacrice economy.

 

[QC]

Re: Dissappointed with gas mileage, any advice?

Jack L,<br /><br />It's an Outboard Johnson unless you're talking about your engine?

 

[BTF112989]

Re: Dissappointed with gas mileage, any advice?

The WOT for my engine is 5000-5500. It is a 2001 Yamaha 150 HPDI. So yours should be around that general area. And if you are at 6000 RPM's all the time no wonder your gas doesn't last you long. I usually go 5300 at the most. I just don't want to push it.

 

[BTF112989]

Re: Dissappointed with gas mileage, any advice?

The WOT for my engine is 5000-5500. It is a 2001 Yamaha 150 HPDI. So yours should be around that general area. And if you are at 6000 RPM's all the time no wonder your gas doesn't last you long. I usually go 5300 at the most. I just don't want to push it.

 

[Pony]

Re: Dissappointed with gas mileage, any advice?

Originally posted by BTF112989:<br /> The WOT for my engine is 5000-5500. It is a 2001 Yamaha 150 HPDI. So yours should be around that general area. And if you are at 6000 RPM's all the time no wonder your gas doesn't last you long. I usually go 5300 at the most. I just don't want to push it.

Yeah 6000 may or may not be right...I dont know but others here or your manual will.........<br /><br />BTF- He may be burning more fuel at WOT as all engines do.......BUT regardless of that fact 20 gallons in 15 miles is WAAAAAY to little. <br /><br />Its my understanding that on avg a 150hp motor will burn roughly 15 gallons of fuel per hour. So a 20 gallon tank should last a little over an hour, like an hour and 20 min or so.......using 30mph as a VERY CONSERVATIVE mph, that tank should yield 40 miles. IMHO

 

[BTF112989]

Re: Dissappointed with gas mileage, any advice?

I am lucky that I have a 62 gallon tank on my boat. I am usually more concerned with my fuel going bad because I don't run enough to use 60 gallons of gas every outing. They put huge tanks in ocean going boats.

 

[steelespike]

Re: Dissappointed with gas mileage, any advice?

If your motor uses a typical outboard fuel pump<br /> it may have a hole in the diaphram letting gas leak into the crankcase.<br /> If you run your motor at 6,000 rpm most of the time I think besides using a lot of gas your using a lot of engine life as well.