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JimBuck

Determining MPG/GPH on an outboard engine...

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I'm heading north of the border in a few days and was wondering how you guys determine your MPG/GPH on an engine. I'm in the process of planning a few routes and was wondering just how much gas I'll need. I have an 88' Mariner 45hp. on a 16ft. Sylvan Backtroller Alum. Hull. It has no gauges hooked up to it for displaying miles, hours etc. She's been known to guzzle gas but I haven't figured out specifics.

I was thinking of just putting in a 1/2 tank of gas and running it at nearly wide open throttle until she runs dry. While doing this I would have my GPS on and keeping track of miles traveled etc. Anyone else care to shed some light on the issue?

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That's as good a means to determine your MPG than any. Many outboard gas consumption rates are based on running time at WOT(Wide Open Throttle), not miles traveled. But both figures would be potentially valuable.

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Fill your tank, go out with GPS and spin around the lake a few times (10minutes or so). FIll you tank and see how much was used. Divide your Miles by how many gallons you used and that sould give a fairly good estimate on gas usage.

Then plug that into how many miles you plan on using on your trip.

I wouldn't waste a half/tank and the time it takes to burn that much fuel just to see your ratio.

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Running at WOT will give you a "worst case" picture, too. As much as I like running at WOT, I have found that my outboard uses way less gas if I run it at 2/3 to 3/4 throttle. I'll bet it uses nearly twice as much fuel at WOT.

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The biggest key to getting the best gas mileage is controlling your rpms. The lowest throttle setting that easily keeps your boat on plane is going to give you the best mpg and the longest cruising range for your boat.

I have a 175 Optimax with Smart Craft gauges, and they tell me my fuel consumption in Gallons Per Hour. I don't know how well these numbers will match up to your '88 Mariner 45 hp motor, but you can see the trend.......

WOT with my boat is about 5700 rpms, 50 mph and 17 gallons per hour -- works out to 2.9 mpg

5000 rpms gets me about 43 mph and 13 gallons per hour --- about 3.3 mpg

4000 rpms gets me about 36 mph and 9 gallons per hour --- now it's up to 4.0 mpg

3300 rpms gets me about 30 mph and 6 gallons per hour --- now we're talking 5.0 mpg

I don't run slower than that very often so I don't know those numbers.

You can see the improvement in gas mileage, from less than 3 mpg at 5700 rpms to 5 mpg at 3300 rpms. My boat has a 36 gallon tank so my cruising range on a tank of gas is 104 miles at WOT or 180 miles at 3300 rpms. It makes a big difference when doing a lot of running.

Hope that helps. One other thing ..... bring plenty of gas (and oil). And have a great trip.

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i dont want to know what mine is! i just keep a 1 gallon can in the boat somewhere and only use it if you run completly out.. 1 gal should be enough to get you to some sort of safety.. put 1 gallon in your tank then go on google earth, measure 2 land marks

drive back and forth till you run out..

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My friend's island camp usually uses about 5 gallons of gas per day with 15 hp motors on 16ft plain tin boats.

My boat uses 3.5-7 gallons per day with a 90 Optimax on a 1750 Lund Outfitter (I usually take 50 gallons for a 7 day trip and have plenty left over).

My friend uses 7-10 gallons per day with a 1976 Evinrude 85 hp on a 16 ft walk-thru.

We run anywhere from 5 to 15 miles out and back. We use electric trolling motors and the 15 hp's don't use trolling motors.

Hope that helps.

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The biggest key to getting the best gas mileage is controlling your rpms. The lowest throttle setting that easily keeps your boat on plane is going to give you the best mpg and the longest cruising range for your boat.

I have a 175 Optimax with Smart Craft gauges, and they tell me my fuel consumption in Gallons Per Hour. I don't know how well these numbers will match up to your '88 Mariner 45 hp motor, but you can see the trend.......

WOT with my boat is about 5700 rpms, 50 mph and 17 gallons per hour -- works out to 2.9 mpg

5000 rpms gets me about 43 mph and 13 gallons per hour --- about 3.3 mpg

4000 rpms gets me about 36 mph and 9 gallons per hour --- now it's up to 4.0 mpg

3300 rpms gets me about 30 mph and 6 gallons per hour --- now we're talking 5.0 mpg

I don't run slower than that very often so I don't know those numbers.

You can see the improvement in gas mileage, from less than 3 mpg at 5700 rpms to 5 mpg at 3300 rpms. My boat has a 36 gallon tank so my cruising range on a tank of gas is 104 miles at WOT or 180 miles at 3300 rpms. It makes a big difference when doing a lot of running.

Hope that helps. One other thing ..... bring plenty of gas (and oil). And have a great trip.

Thanks for that post. I wonder if we'll ever see outboards getting 20+ mpg

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Excellent. Thnks guys. This gives me a good idea as to what I'm dealing with here. I've got 12 gallons worth of gas space and just picked up a few gallons of oil for the week. I guess I'm gonna have to stop at a place or two to fill up during the day.

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I would guess you're in the 4-5 MPG range. I had a 2001 90 HP Merc carb that would calculate out to 3-4 MPG using my GPS.

Just got back from Leech with my friends boat and he got 8 MPG with his 40 hp Suzuki 4 stroke EFI on a 1650 Crestliner Fishawk. That's the higest I've ever seen.

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