What is the right gas to use?

[mcgill]

Hello



what type of gas do you use in your yamaha i am useing 87

 

[JB]

Re: What is the right gas to use?

87 octane unleaded regular in USA should work just fine, mcgill. Some other places it is rated 91 octane.

 

[Scott Danforth]

Re: What is the right gas to use?

I recommend looking for ethanol free fuel if possible.

 

[RandyJ]

Re: What is the right gas to use?

Older motors were built back in the days of 98/100 octane gasoline. Until they came up with the higher compression engines I never heard of 87/89 octane gasoline... it still burns in old motors but not nearly as good. I've got a couple of old mercruiser 140's that I'm convinced that the low octane and ethanol is the big problem. I'm not sure what year the conversion came to be but after that period pretty much all motors were built to handle the lower octane. Ethanol was pretty much added simply to extend the gasoline.... like putting more water in your coffee so you'll have a full cup of coffee.

 

[JB]

Re: What is the right gas to use?

What planet did all that "information" come from, Randy??

98/100 octane gas has never been marketed in this country, except for aircraft use.

Ethanol is added to raise the octane rating of gasoline, not to "extend" it.

If you have trouble with your Mercruisers, tell it to the Mercruiser forum, not the outboard forum.

Back in my "old days" we ran outboards on 80 octane unleaded "white" gas when we could find it.

 

[coleman kayak1]

Re: What is the right gas to use?

Per my yamaha manual 86 octane or higher, in other words regular will be fine. The only advantage to plus or premium is higher octane, which reduces or eliminates pinging in higher compression motors, nothing more than a waste of money in something that only requires 86 IMHO.

Ethanol (E10) can cause problems with fuel lines, gaskets, etc, and its been known to collect water worse. I would recommend using an ethanol treatment, its more economical than finding and buying non-ethanol fuel at least in my area.

In run regular unleaded with Sta-Bil and Ethanol treatment in every tank. Oh and two stroke of course

 

[RogersJetboat454]

Re: What is the right gas to use?

Older motors were built back in the days of 98/100 octane gasoline. Until they came up with the higher compression engines I never heard of 87/89 octane gasoline... it still burns in old motors but not nearly as good.

Higher compression engines use high octane fuel. High compression engines are more likely to have issues with detonation, hence the need for higher octane fuel which burns SLOWER than low octane fuel.

I've got a couple of old mercruiser 140's that I'm convinced that the low octane and ethanol is the big problem.

Sounds like you have mechanical troubles with your 140's. Cylinders may be carboned up, and fuel system needs to be cleaned and upgraded to handle E-10

I'm not sure what year the conversion came to be but after that period pretty much all motors were built to handle the lower octane.

Engine compression ratios started to drop in the early 70's.

Ethanol was pretty much added simply to extend the gasoline.... like putting more water in your coffee so you'll have a full cup of coffee.

Wrong...
Ethanol took the place of MTBE which was outlawed a few years ago, due to the fact that MTBE does bad things to ground water. Both are octane boosters, like the old Tetraethyl-lead.

 

[RandyJ]

Re: What is the right gas to use?

Pray tell... what was the octane rating in the old days when you pulled up to a pump and asked for regular or ethyl... and you didn't have to pump your own gas? And why is it that old chevy v-8's were considered normal if they had 120 psi compression but nowadays seeing 160 psi is common in automobiles? And, yep, I'm a bit familiar with aviation fuel. I do know that there were changes in the compression and various other engineering details to allow for more complete burning of HC fuels. Let's not confuse psi test compression with compression ratios... as I remember, prior to the early 70's the leaded "ethyl" was commonly 98 octane in the U.S.A. I don't recall exactly what the octane ratings were so.. mia culpa on that one... but I do know av gas has run like 100 - 101 octane.

 

[coleman kayak1]

Re: What is the right gas to use?

Per this site http://inventors.about.com/od/gstartinventions/a/gasoline_2.htm

By the mid-1920s, gasoline were 40 - 60 Octane.

During the 1950s, the increase of the compression ratio and higher octane fuels occurred.

It is true newer automotive engines have higher compression. This is a reason many of them are requiring plus or premium grade fuels. Octane helps prevent detonation or pinging. Higher compression ratios lead to pinging. Running 93 octane in an engine that only requires 86 is just a waste. If it requires 93, run 93. If it requires 89, run 89. If it requires 87, run 87. Anything else is a waste.

In any case, I do not believe automotive gas has EVER had a higher octane rating than 93 or so. If the vehicles had lower compression, that would mean the need for less, not more octane.

 

[99yam40]

Re: What is the right gas to use?

Seems like I remember the owners manual for a 68 Chevy PU I once owned with a 300CID straight 6 called for regular fuel with octane rating on 97. Do not have it anymore so I can not see how good my memory is.
Back in the 60's and early 70's the stickers on the premium pumps were over 100 octane but not much over, from what I can remember

I agree it is a waste of money to by higher than motor needs/is designed for

 

[RogersJetboat454]

Re: What is the right gas to use?

And why is it that old chevy v-8's were considered normal if they had 120 psi compression but nowadays seeing 160 psi is common in automobiles?

What era and form of old Chevy V8 are we talking about? The family hauler isn't going to have an 11:1 compression ratio like a DZ302 Camaro, or LS6 Chevelle. An engine only capable of generating a "normal" pressure of 120 PSI will run on high octane fuel, but doesn't need high octane fuel.
An engine of that era with the high compression ratio will undoubtedly require the high octane fuel to stay happy.

A cross comparison of engines back then to engines of today is apples and oranges. Engines of today benefit from aluminum heads, better combustion chamber designs, better piston designs, knock sensors, oxygen sensors, air flow meters, multi-port or direct fuel injection.

 

[Scott Danforth]

Re: What is the right gas to use?

In any case, I do not believe automotive gas has EVER had a higher octane rating than 93 or so. .

BP Ultimate 102 was 102 octane. in the US, the highest you will find in abundance is 94 octane. However in many countries, 98-102 is common.

However the best fuel for marine or small engine use is fuel without ethanol