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Fuel range capacity.

arko

New member
What would be the average fuel consumption or running time for a Mariner 75hp 2 stroke. The engine is pretty well tuned. Im using the 50:1 oil mix and no other additives. I will be using her for speed some days and cruising on others. I ahve yet to test this and was just wondering if anyone can give me a heads up on a typical consumption of a 12 liter tank.
Thanks.
 
General rule of thumb:

A 2 stroke outboard will use 10% of it's horsepower, in gallons at full throttle. So 75 horse will burn 7.5 gallons per hour at full throttle.

At "cruise speed", which is generally somewhere in the 3000-4000 rpms range (different on every motor), which is reached when the timing on the motor is fully advanced but you still have some throttle left (so between 2/3 and maybe 3/4 throttle on the average motor) you will generally burn about 60% of max - so in this case, perhaps 4.5 gallons per hour.

Of course numerous factors affect fuel consumption including condition of the motor, how well it's tuned, how much weight you have on the boat, hull shape (a pontoon boat is like trying to push a dock loaded with rocks through the water compared to a deep V ski boat), the condition and cleanliness of the hull etc.

A 12 liter tank (which is roughly 3 US gallons) is what I use on my 10 horse and lower motors. In fact any "portable" tank would be pretty small for a 75 horse motor unless you simply used it to buzz out to a fishing hole and then buzz back.

As you can see from the number, while not exact, even if you were only cruising for say 3 to 5 hours, you would probably minimally want 25 or 30 gallons (100-120 liters) to allow for what you would burn plus a bit for safety.

If you wanted to "throttle" around for two hours, you could suck up 15 gallons (60 liters) in fairly short order.

Last note, there is no magic in a can, add on's, whale tails, dolphin tails, tabs, slicks etc that will add more than the most minimal performance increases and lower fuel consumption.

By using an adjustable jack plate and a fuel flow meter I was able to rig my 140 horse to average .2 gph better (that's "point 2") at cruise. Now over a whole season that translates into quite a few gallons, but only because each time I fill the tanks (plural), they hold 40 gallons each. Each tank gives me about 5 hours of cruise time (at cruise speed), so saving a gallon per "tank" over the season is worth it - but the cost of running is still considerable.
 
Wow. I didnt realise it would use that much. I have purchased extra tanks but its finding the right place and balance to secure them. I actually did think this was a bit big for the boat itself. Maybe I should look at a smaller engine? Thanks for your help.... much appreciated.
 
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