Something to think about between flights

Tom Scholberg

Tom Scholberg

Well-known member
After spending quite a bit of time with a Sawsall cutting out my Broadbill's built in gas tank I thought this might be a good place for some discussion on fuel tanks.
First point is that gasoline today has a VERY short shelf life as in days not months. Some of that is to blame on ethanol but that is a separate discussion.
Second is the fuel consumption of most (older) outboards. A pretty good rule of thumb is to move the decimal point once to the left on the horsepower number will give you gallons/ hour at full throttle. Example: a 25 hp. will use 2.5 gallons of fuel per hour at full throttle. I did find this one to be true the hard way one day several years ago.;-)
SO if we have a six gallon tank that will give us 6/2.5=2.4 hours of wide open running. If we are honest with ourselves do we do that very often?? Also remember that running at a slower speed stretches that number quite a bit. Also newer outboards especially 4 strokes are a whole lot more thrifty.
After using my Poleboat for most of my hunting the last couple years I realized that what was in the gas tank ceased being usable fuel a long time ago.
My Poleboat sometimes wears a 4 hp OMC that uses the same tank as my 25 on the Broadbill so I have a 3 gallon tank that has fresher fuel and takes up less space.
So if I need more fuel I will take a second 3 gal. tank.
Any thoughts? After all this is a forum.
 
Tom,

I run a 25hp on my BBIII and if I'm going to be running around a lot or towing another boat I use a 6 gallon tank and will also carry a spare 3 gallon tank. I try not to keep anything in the tanks unless I know it's going to be used quickly. As for todays fuel, it does go bad quickly. I try and use stabilizer in any fuel that I know is going to sit for a little while. A little while being more than 3 weeks or so.
 
My fuel use really varies on the location I am hunting.
Some mornings, the motor barely warms up before I am to my spot. Others, its a 5-7 mile ride each way.
Some days I use a couple of cups of gas, others 3-4 gallons.
Given that variation, I have to keep my 6 gallon tank full, don't want to get caught short.
But I also use heavy dose of stabilizer in every gallon I add.

Most years, my boat is run 10 months out of the year and fuel issues have not been a problem.
This year has been an exception, I haven't run the boat in 6 months (a "record" for me since buying my first boat 20 years ago) and will be checking the tank & fuel for water before the season starts.
I intend to completely empty the tank into a 5 gallon pail and check for water, separation, etc.. If I see any sign problems, that fuel will go to the recyclers.
If not, I will add a bottle of sea foam, filter the gas as I re-pour into the tank and crank her up.

If I were running a smaller more efficient 4 stroke, I would use a 3 gallon tank, less gas to go bad.
 
Tom,
I switched to 2 3-gal tanks for my duck boats a number of years ago. I too rarely ran the 6 gal tank dry and gas sat and sat and got mixed with 2 or 3 gal of fresh and then again. I never knew the condition of the gas. Switching to the 3gal tanks lets me completely empty each tank alternately. It also serves to reduce the weight carried or at least allows it to be better distributed. When I feel I need the full 6 gallons along I'll pour the remaining gas in the partially filled tank into another container allowing me to fill the 3 gal tank fully and get the oil mix right. I then use the saved premixed gas to top off the tanks later. This works much better for me then running 6 gal tanks.

Scott
 
That is an interesting approach, I may look into getting a couple of 3 gallon tanks!
 
I think the conventional wisdom for fuel is 1/3 out, 1/3 back, 1/3 for unforeseen circumstances. At least that is how we always figured it for offshore trips. My mudboat is ~36hp. I carry 6 gallons of fuel to my usual haunts knowing I will only burn a maximum of 2/3 of my fuel. If there is the potential for any detours, or for exploring new spots, I'll carry either an extra 2 or 5 gallon can (or both).

I have room for a larger primary fuel tank and would prefer to carry twice as much, but as mentioned previously, it is better to treat fuel as perishable these days.
 
I would guess I go through about 3 to 5 six gallon tanks a season in my boat. I top off the tank when it gets to be about half full. I don't worry about it going bad over the 3 month span just like I don't worry about the gas going bad in my truck becasue it is being used and sloshing around in the tank as I muddle through the 107 day season. However at the end of the season I dump what is left in the tank into my truck because my boat most likely will not be used for at least 4 months. That way I start the summer off fresh. I currently have an Etec so no mixing with oil. But I did the same when I had my old Suzuki when I did mix. With the mix I would add a gallon to my truck at time when it was on a full tank to dilute it down. Never had an issue doing this and this way I start every summer with an empty gas tank in the boat and no bad gas to dispose of.
 
I use the small tank on my rig, and I use seafoam to "stabilize" - and use stabil in addition If it's gonna sit.


And I always (when possible) use non oxy fuel. It's available at fleet farm now, and at the gas station next to the lake I hunt.
 
I've been using two 3 gallon tanks for the last ten or so years. I run a twenty-five two stroke. Add to the above suggestions, it's a lot easier to put a full three gallon tank into the boat than a full six gallon. Plus I agree on the running them dry.


I also use plenty of either Seafoam or Stabil Marine, depending on what is available.


Jon
 
So how does "unfresh" gas affect the motor? Facts. not guesses. I don't kwo and thus the question. I have a 6 gallon tank on my 15 hp. I probably run through 20 gallons of gas in a season max. Then the motor and gas sit until fishing season (which never happened thisi summer) and then run again at the start of hunting. Never had a problem with the motor starting, motor running, no motor troubles etc... I've been doing it this way for as long as I can remember whether it is this motor or any of the previous motors we have had.

Now, on my smaller weed whip type motors, fresh gas all the time. Same with lawn mower and snow blower as they don't start without fresh gas.

Mark W
 
Interesting stuff. I run an old 40 hp Yamaha 2 stroke on one boat and a newer 4 stroke Suzuki on my little 14 ft'er. The older 40 starts easy and runs well on old gas but the 4 stroke is fussy. Seafoam definately helps.

I was just out for a longer trip with the 40 last week running about 80 miles on a lake as fast as possible and got about 1.5 hrs of running time on a 5 gal tank. I think I run at about 30 mph if the boat isn't loaded too heavy and the water is flat calm.

I used to put additives and stabilizers in all my combustion engines for the off season but concluded it wasn't worth the time. Condensation putting water in my fuel seems to be the most common problem with leaving things over winter, so if they run rough when I fire them back up, I'll try gasline antifreeze, or Seafoam if that doesn't work.

Mike
 
So how does "unfresh" gas affect the motor? Facts. not guesses. I don't kwo and thus the question. I have a 6 gallon tank on my 15 hp. I probably run through 20 gallons of gas in a season max. Then the motor and gas sit until fishing season (which never happened thisi summer) and then run again at the start of hunting. Never had a problem with the motor starting, motor running, no motor troubles etc... I've been doing it this way for as long as I can remember whether it is this motor or any of the previous motors we have had.

Now, on my smaller weed whip type motors, fresh gas all the time. Same with lawn mower and snow blower as they don't start without fresh gas.

Mark W
Click to expand...
Marine Stabil is a good choice as an additive.

Older outboards have plastic parts in the fuel delivery system that can absorb the water "pulled" into ethanol containing gasoline, causing these to swell and alter fuel flow. Fuel break-down deposits varnish in the carb. bowl. Phase seperation can occur within weeks in E-10 gasoline in open fuel delivery systems like a boat, faster if the hull is sitting in water. Have a conversation with a small outboard mechanic, he will not say kind things about the ethanol containing fuels. I had the vent canister float jam on my Verado 225hp on my Conquest 235 (I was told that the recall replacement had been done when I took delivery on the boat from Nisswa Marine-eventually I received a check to reimburse me for warranty work not conducted), luckily, when the boat died when the float swelled and jammed, I was all of four hundred feet from the marina entrance, so all I had to do was throw out my bow anchor and put a call in on my radio for a friend to tow me to the marina. I salmon fish the waters in archepelago island chain between the tip of the Door Peninsula and Pte. Detour-not many folks around if you get in trouble on the open lake, particularly at night-miles of dolomite limestone cobble coastline.

Mercury Verados were designed to run on ethanol containing gasoline up to E-20 (except the 300hp). Apparently a parts supplier didn't get the memo. with the specifications...
 
Since last year I just run high test gas, 91 octane, that supposed to be ethanol free. I just get Shell 91 octane. Heard other's still have ethanol in their premium gas.
Since switching over I haven't been having any problems and all my 2 cycle motors have been running better. Can leave it sit for a couple of months and it starts right back up. Go with ethanol free premium gas and it is worth the cost not to have any issues with your outboard.
 
I presently live on Hilton Head Island after spending many years in Michigan. Water in the gas gave me fits my first years down here in Carolina. I finally bought a device called an "EZ Siphon" and after every boat trip, I siphon the left over gas into one of my vehicles. I only use fresh 89 octane gas each time I go out in my boat.
Larry
 
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