Gas milage from a 9.9 hp Merc?

Terry Desilets

Terry Desilets

Active member
I haven't owned an outboard newer than 40 years old EVER! I have recently come into possession of a 96 9.9hp Mercury 2 stroke. To be used as my primary power on my 12' Aerocraft. In the past, I wouldn't leave the dock with less than 6 gallons of fuel. With my 35hp, it was 12 gallons.

Now the old iron is quite notorious for how thirsty they are. With this newer engine, can I expect greatly extended operation? Do I pack a 3 gallon or do I keep the 6 gallon tank? Typically, I travel 1-3 miles each way, but then there's a couple miles for the inevitable sightseeing.
 
I'd go for a ride this summer with a backup tank and see how much you use. A GREAT excuse to get out on the water.
 
I'd definitely pack the 6 gal tank until you figure it out, but I bet the 3 gal tank will get you though most days.

Nate
 
Fun fact to know and tell your friends about old iron fuel consumption. Move the horsepower decimal point once to the left and you have gallons per hour at full throttle. example, 25 hp = 2.5 gallon/ hr. at full throttle. Of course this is only aprox but it is surprizingly close. New ones are MUCH less and 4 strokes are unbelievably thrifty to run. Good luck. I also would just use this as an excuse to get out on the water this summer also, dirty job but someone has to do it.;-))
 
Terry, I run a 97 Merc 9.9 on my Chuck Huff. With 6 gallons stored under the bow I run all weekend long and run about the same as you 1-3 miles each way to various blinds. I dont run full out in the smaller guts but on the big water I do. I'm very happy with the milage I get with the tank and motor combo.

Bill V
 
I had the same motor on my last boat. 6 gallons would last a very long time. We would go 4 miles out and 4 miles back and could easily do it many times before needing to refill the tank. I'd say about 3/4 of that distance was at full throttle the rest at putt putt speed.

Loved that motor - more so than the curent 15 hp Evinrude.

Mark W
 
I'll run it around this summer, but being a boating family, my duck boat usually isn't pulled out until the end of August. It's been a long Winter, I'm just sitting here dreaming....

Tom: That is an interesting tidbit! And pretty close to what I know about my engines. On my '58 35hp, I figure 4 gal hr to be safe. I installed a fuel pump and have a 16 gal tank. Love that old iron!

Some of this comes down to space consideration. It's a 12ft boat and I can only fit so much crap into it. My rig is cork and cedar so I just can't pile them in. Luckily I'm a low tech hunter and pack pretty light. But then, I don't want to cut myself short on fuel. More testing is needed.....

Many thanks for your insights, I'm itching to be on the water, cabin fever is getting to me.
 
Terry,

The time honored rule is the rule of thirds; a third of your fuel supply to get there, a third to get back and a third in reserve.

For the mileage range you give, I would think that a three gallon tank will be sufficient however, three gallons will still be a limiting factor in the scouting runs you may wish to take.

A lot depends on how disciplined you can be in respecting your fuel range. I have areas in which 3 gallons would be plenty because they are so small of an area, I’d have to run in circles to burn up all my fuel.
Other spots I hunt, the 6 gallon tank would be best because then fuel would not be a limiting factor if I did decide to check out that other spot , or the spot after that, or the one just around the bend, or,,,,, well you get my drift.

So, can you respect you fuel range or do you want more freedom? The choice is yours to make. :>)
 
Back when I ran a 1986 9.9hp 2 stroke on my old 1440 mv jon, I could run upriver 10 miles and back and always had at least a gallon left from a full 6 gallon tank.
My 1999 18hp Nissan seemed to be just as thrifty. Probably because I ran the 9.9 wide open while the 18 was running around 3/4 throttle.
 
I have a 97 9.9 Merc and run it on my Arthur Armstrong Wigeon(glass boat from NC). I have a 3 gallon tank and have never considered a 6. I usually run around 2-3 miles out to where I am hunting, sometimes a little farther. The most I have used just running around scouting for a few hours is maybe 2 gallons. I would say I run it wide open most of the time in the straightaways while slowing through curves and turns. We have about a 4-5' tide so there is generally some current.
 
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