Boat gas

[Shellkat]

I have a 1976 Johnson 85 up on the back of a 1860 tracker. I built this boat from a blank hull. This is the second boat I have had it on.I have had the motor for 20 years and its been to Canada multiple times and everywhere inbetween. Never let me down and I run the crap out of it. My only problem is it likes gas. A 20 gallon tank doesn't last long. I can run from dam on the big c to the end of beaver creek and back. Are the newer motors or even 4 strokes that much better on mileage. Never had much to compare to. I have had very little problem with this motor except those junky Walmart fuel lines. My GPS says I'm running 44 at full throttle.

[smbass1]

You will get much better gas mileage out of a four stroke but I'm not sure if the cost will make up for the cost of a new motor. The one great thing about four stroke motors is you can troll all day and it won't foul out the plugs. Also very quite you can hardly hear it running.

[CaptObvious]

Shellkat, I have a Johnson 90 on my 1990 tracker deep v and same thing. Gas hog! I believe it's a 1989 model. Love it.

[adam7456]

A general rule on 2 stroke boat engines is you will burn 10% of the engine HP size every hour at wide open throttle. Your 85hp engine should use approximately 8.5 gallons per hour giving you just over 2 hours of run time.

I have a 1998 90hp engine with a 24 gallon tank and that's about right. One way to get better gas mileage is not to run wide open. The most efficient RPM range will be somewhere between 1/2 to 3/4 the max RPMs of the motor. You would have to try different RPMs and see what works better for your specific boat. Of course it isn't as fun to drive slower.

[Moveon]

A general rule on 2 stroke boat engines is you will burn 10% of the engine HP size every hour at wide open throttle. Your 85hp engine should use approximately 8.5 gallons per hour giving you just over 2 hours of run time.

I have a 1998 90hp engine with a 24 gallon tank and that's about right. One way to get better gas mileage is not to run wide open. The most efficient RPM range will be somewhere between 1/2 to 3/4 the max RPMs of the motor. You would have to try different RPMs and see what works better for your specific boat. Of course it isn't as fun to drive slower.

What type of propeller do you run. 3 blade or four blade and what is the pitch of the blades. And like was said above running at 3/4 full rpm will save money on gas. It takes much more energy to go full throttle than 1/2 or 3/4 throttle.

Reducing drag helps if you can find a way to do that. Clean the bottom of the boat and keep it clean and streamlined. Anything that can reduce the friction between the water and the boat helps too.

Of course the tilt of the motor can make a big difference too.

I've got an older Johnson 35 HP which is a 1978 model. It still runs good to this day and I bought it back in the late 1970's. I run some sea foam though it from time to time and change out the spark plugs once in a while. I use good premium oil in the gas and mix it correctly. I'll add some stabile to the gas to prevent it from going bad if I have to store the gas in the tank for the winter.

Summer gas has a lower vapor pressure due to USEPA regulations that require the Refineries to reformulate the gasoline in certain areas of the country to help lower evaporative emissions of hydrocarbons that help form "Ozone". So the gas may not give you as much "KICK" in the summer time as in the winter months. It's more volatile in the winter months. This can effect your gas mileage and power I would guess.

[GeoFisher]

I have a 1976 Johnson 85 up on the back of a 1860 tracker. I built this boat from a blank hull. This is the second boat I have had it on.I have had the motor for 20 years and its been to Canada multiple times and everywhere inbetween. Never let me down and I run the crap out of it. My only problem is it likes gas. A 20 gallon tank doesn't last long. I can run from dam on the big c to the end of beaver creek and back. Are the newer motors or even 4 strokes that much better on mileage. Never had much to compare to. I have had very little problem with this motor except those junky Walmart fuel lines. My GPS says I'm running 44 at full throttle.

That is one OLD ASS Tracker...you sure it needs gasoline, and not COAL??

[peter]

I had a 70hp 1984 Johnson on a 17' sea nymph alum v hull. Documented it many times at 5-6 mpg at maybe 75-80% throttle (30 mph relatively smooth water loaded with weight). This was on 700-1000 mile long river trips. Got another identical boat and motor but 1987 and it was worse mileage but seemed to have more power. At full throttle it is ridiculously less milage. If yours is the same block as the 90 it is quite a bit worse mpg than the 70 according to a Johnson master mechanic I asked.

I think the milage seems worse when you are changing six gallon tanks all the time. The oil is expensive too.

Now have a 2000 carburated honda 90 on similar boat and an 18 gallon tank. Put gas in it about once a month and fish pretty must most weekends. No idea what the milage is but it sure sems much better. At full throttle it burns it real fast though.

Those old johnsons are great motors. I ran that first one on various trips 12-14 hours a day at 30 mph for five to six days in a row (total 6-7 thousand miles) plus fishing in it a ton for twenty years. The hull went bad but the motor is now on a boat on the ohio of a catfisheerman you probably know that fishes the grain silos and does auto body repair in Jeffersonville.

Keep the Johnson. Put in at a ramp near where you are going to fish.

That mechanic who was in Ohio on the Ohio River told me he knows of workboats with 20,000 hours on the old johnsons.

If you are getting as little. 3 miles a gallon you might run the numbers.

If you want to know the milage get a river chart and cruise up to Madison early in the am when it's smooth. Fill it up when you leave and get back. Maybe GPS would work for the distance too.

More than you wanted to know...

[peter]

You have a photo of jem you can post here?

[Wormin]

I get around 2 mpg with a 200hp on a 18'foot boat, with a 48gal tank I still can't crack 100 miles on a tank of gas. But I guess it goes with the Territory before this boat I had a 14 trimcraft with a 55 rude and could fill a 6 gal metal tank a run half the summer on it.

[Shellkat]

Geo, boat is 2014, motor is 1976

[Shellkat]

I can't upload photos, I get to screen that says choose file and it won't do anything from there

[peter]

I had a 70hp 1984 Johnson on a 17' sea nymph alum v hull. Documented it many times at 5-6 mpg at maybe 75-80% throttle (30 mph relatively smooth water loaded with weight). This was on 700-1000 mile long river trips. Got another identical boat and motor but 1987 and it was worse mileage but seemed to have more power. At full throttle it is ridiculously less milage. If yours is the same block as the 90 it is quite a bit worse mpg than the 70 according to a Johnson master mechanic I asked.

I think the milage seems worse when you are changing six gallon tanks all the time. The oil is expensive too.

Now have a 2000 carburated honda 90 on similar boat and an 18 gallon tank. Put gas in it about once a month and fish pretty must most weekends. No idea what the milage is but it sure sems much better. At full throttle it burns it real fast though.

Those old johnsons are great motors. I ran that first one on various trips 12-14 hours a day at 30 mph for five to six days in a row (total 6-7 thousand miles) plus fishing in it a ton for twenty years. The hull went bad but the motor is now on a boat on the ohio of a catfisheerman you probably know that fishes the grain silos and does auto body repair in Jeffersonville.

Keep the Johnson. Put in at a ramp near where you are going to fish.

That mechanic who was in Ohio on the Ohio River told me he knows of workboats with 20,000 hours on the old johnsons.

If you are getting as little. 3 miles a gallon you might run the numbers.

If you want to know the milage get a river chart and cruise up to Madison early in the am when it's smooth. Fill it up when you leave and get back. Maybe GPS would work for the distance too.

More than you wanted to know...

Sorry shellkat. I thought geo made the original post... In case you didn't know some of what I was talkin about.