1995 Yamaha C85 fuel consumption has increased.

[Michael B]

I have to ask....is the bottom of the boat clean?

Yep. Boat is on a trailer.

[Michael B]

I am fairly sure all 3 cylinder Yam motors use the crankcase pulse of #3 cylinder to power the fuel pump

also running at different RPM or loading of the boat will cause different fuel usage.
different wave/water conditions will change usage too
did you change props or damage the prop someway?

Thank You. I've been boating for 40 yrs and know boats. I've put 1200 hrs on this motor and know my boat. After checking mileage countless times I know what the fuel burn is.

I simply asked two question in my post and not one answered them. People just guess and I'm not looking for that. I'll figure it out. Thanks for everyone's input.

[boscoe99]

The difference in compression is not doing it. Atmospheric differences (that can affect compression) are more likely to also result in a change of power and performance than will that small amount of compression reduction. Might be a bit of both. Atmospheric conditions can also result in both low compression and a reduction is power output/loss of performance.

An engine idling may never create enough heat to cause the water temperature to rise to the value that will cause a thermostat to open.

You asked specific questions. I have now given you my answers (right or wrong) to those specific questions.

You also asked what people think. Three questions, not two. You have gotten a number of answers from others to that question.

Problems are hard to determine at times in person. Very hard to do from miles away behind a key board.

Information that others took time and effort to give you are worth every bit of the price that you paid for the information.

[panasonic]

Thank You. I've been boating for 40 yrs and know boats. I've put 1200 hrs on this motor and know my boat. After checking mileage countless times I know what the fuel burn is.

I simply asked two question in my post and not one answered them. People just guess and I'm not looking for that. I'll figure it out. Thanks for everyone's input.

So you have about a 14% reduction in fuel mileage for some reason. The compression has dropped about 4% if your gage is reading accurate. Is this the cause of the problem...I don't know. What is the spec for that engine...if there is one.

As for the thermostat. Some engines have a hard time getting up to proper operating temp on the muffs, the engine is just not working hard as you know. You said you were only getting 100 degrees and the thermostat is 122...so that tells me it not gettling there.all I can say is put it in the water under load and take your Temps again.

You also said you were changing the the thermostat....did you do that?

That's all I can give for possible answers and additional questions.

As said already folks take their own time to try and help others for free and because they get some satisfaction from doing it. Many many people have got their problems solved here.

Good luck with your engine.

[robert graham]

3.23 to 2.76 looks like about 1/2 mile per gallon....could current, wind, boat loading, other factors account for this aparent loss of efficiency?.....

[robert graham]

Mine is a 1999 C90 Yamaha similar motor to yours, so I have 19 years of experience on these motors....so I'm very interested in your issue, problem, whatever, but most folks on these forums, myself included, can only venture our ideas regarding causes or solutions for you....so be patient and possibly/probably an answer/solution should appear....

[Michael B]

The difference in compression is not doing it. Atmospheric differences (that can affect compression) are more likely to also result in a change of power and performance than will that small amount of compression reduction. Might be a bit of both. Atmospheric conditions can also result in both low compression and a reduction is power output/loss of performance.

An engine idling may never create enough heat to cause the water temperature to rise to the value that will cause a thermostat to open.

You asked specific questions. I have now given you my answers (right or wrong) to those specific questions.

You also asked what people think. Three questions, not two. You have gotten a number of answers from others to that question.

Problems are hard to determine at times in person. Very hard to do from miles away behind a key board.

Information that others took time and effort to give you are worth every bit of the price that you paid for the information.

Thank you for your answers.

[Michael B]

So you have about a 14% reduction in fuel mileage for some reason. The compression has dropped about 4% if your gage is reading accurate. Is this the cause of the problem...I don't know. What is the spec for that engine...if there is one.

As for the thermostat. Some engines have a hard time getting up to proper operating temp on the muffs, the engine is just not working hard as you know. You said you were only getting 100 degrees and the thermostat is 122...so that tells me it not gettling there.all I can say is put it in the water under load and take your Temps again.

You also said you were changing the the thermostat....did you do that?

That's all I can give for possible answers and additional questions.

As said already folks take their own time to try and help others for free and because they get some satisfaction from doing it. Many many people have got their problems solved here.

Good luck with your engine.

Thank You for your answers. I will have my parts Tuesday and hope to fish Thursday. I'll let you guys know. Thanks everyone.

[Michael B]

Mine is a 1999 C90 Yamaha similar motor to yours, so I have 19 years of experience on these motors....so I'm very interested in your issue, problem, whatever, but most folks on these forums, myself included, can only venture our ideas regarding causes or solutions for you....so be patient and possibly/probably an answer/solution should appear....

Thank You Sir

[zenoahphobic]

I would add fuel consumption would not increase that amount if the engine is losing compression through ring wear, all else being the same.
This is because it is a one gear transmission, that is you cannot rev more to make up lost speed.
Therefore there must be a fuel leak if you are really sure your gauge has not gone faulty.

[Michael B]

Little update. With the new thermostat I picked up about ten 10 degrees on the head and thermostat housing while running at 1500 rpm. I use a big trash can. The thermostat is stamped 122 and the I got was 111. As Panasonic said you might not reach operating temp with no load and that seems to be the case here. . I also replaced the fuel pump for preventive maintenance. Going to put it on a local lake tomorrow and give it a test. I don't think I can reach the back of the motor while running but I'll see. The final test is when I go offshore for a full day of fishing and then check my mileage again.

[pstephens46]

Should have asked awhile back.

How is it that an 85 hp motor is getting 3.23 mpg?

Are 2 strokes normally that bad on fuel?

How heavy is this boat?

My F150 is 4+ mpg at cruise at 3800rpm.

3200lbs....

[boscoe99]

Should have asked awhile back.

How is it that an 85 hp motor is getting 3.23 mpg?

Are 2 strokes normally that bad on fuel?

How heavy is this boat?

My F150 is 4+ mpg at cruise at 3800rpm.

3200lbs....

Yes. Not only yes, but hell yes.

Give em hell Harry over on TOS.

[pstephens46]

Yes. Not only yes, but hell yes.

Give em hell Harry over on TOS.

Aggravating them sum beaches best I can. “ Had a loose wire on my port motor and it caused all sorts of problems....Two years later the starboard started giving me problems... “. Just shoot me...

[99yam40]

back in the early 70s I was paying less than 20 cents per gallon for gas, who worried about gas mileage back then

things have changed now, but I never thought we would see gas less that $3 a gallon after it went over $4.
I was shocked we had less than #2 for awhile