Wow, all these years and I've always used regular gas . . .

[Expidia]

Never noticed this before. I always thought Mercs used just regular which is around 87 octane.
This link below from Merc says we need at least 91 octane (Verados need 95 premium)
I've always had to use the middle grade in my two Saab autos, but always figured my 3 Merc outboards only needed regular.

My oldest is a 99. Note engines prior to 1980 even require premium (91 octane) for 30 HP and above.

I don't mind switching up to the 91 octane as for me it's only a 6.5 gal tank, so like another $1.50 per fill.

I could swear I've read through the whole Mercury manual for my 2007 4 stroke when it was new and never caught this.

Ticks me off that this one got by me in that I've been using 87 since the 40 HP 4 stroke was new in 2007 and now I find out it could have been knocking internally (which in a car that's easy to hear) and I've been reducing the life of my engine for the last 5 years!

Off Merc's site:
http://www.mercurymarine.com.au/hom...e/fuel--oils-recommendations---outboards.aspx

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

We use "AKI" (R+M)/2 rating for octane in our gas in the US. That link is for Australian Mercury site . They use RON octane ratings. There's roughly a 4-5 point difference between AKI and RON so 87 octane in the US is equivalent to 91-92 octane in Australia.

You are OK with 87 octane US gas.

 

[Expidia]

Re: Wow, all these years and I've always used regular gas . . .

We use "AKI" (R+M)/2 rating for octane in our gas in the US. That link is for Australian Mercury site . They use RON octane ratings. There's roughly a 4-5 point difference between AKI and RON so 87 octane in the US is equivalent to 91-92 octane in Australia.

You are OK with 87 octane US gas.

Thanks, you are correct. I got home and checked my Merc manual. One would think octane is octane, guess not. Even so, my book says 87 minumum. For U.S. and Canada (outside of the two countries RON 91 minimum) I'm going to move up anyway to the mid grade which for my little 6 gal tank for $1.50 more, I might see a little more performance and possible longer engine life. Can't hurt it!
Thx for that quick reply.

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

Actually you'll get less performance out of higher octane gas if you dont have the compression and/or timing needed for it to be optimized. Higher octane gas burns slower and if you dont need it will not work as efficiently as lower grade gasoline. You'll really get no benefit at all from the higher grade gas. The exception being higher grade 100% gasoline that is free of alcohol.

 

[River Boy]

Re: Wow, all these years and I've always used regular gas . . .

Interesting thread. I would have thought octane values were international, like volts and ohms. I have heard some outboard motors made for sale in 3rd world countries are very low compression made to run on kerosene, (the most available pertoleum in their counrty).

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

It gets even more confusing when you realize the old cheap hot rodder standby extremely stable 100LL aviation gas is actually rated RON and would correspond to around 94 octane by the AKI rating method.

 

[Expidia]

Re: Wow, all these years and I've always used regular gas . . .

Interesting thread. I would have thought octane values were international, like volts and ohms. I have heard some outboard motors made for sale in 3rd world countries are very low compression made to run on kerosene, (the most available pertoleum in their counrty).

Tell me about it! I saw the .au in the link I posted to the Merc document on fuel. Who would have thought octane levels are different in other country's, yet they use the same numbers???

 

[Expidia]

Re: Wow, all these years and I've always used regular gas . . .

Actually you'll get less performance out of higher octane gas if you dont have the compression and/or timing needed for it to be optimized. Higher octane gas burns slower and if you dont need it will not work as efficiently as lower grade gasoline. You'll really get no benefit at all from the higher grade gas. The exception being higher grade 100% gasoline that is free of alcohol.

Yes, I grew up around car engines and that's what I always believed that the engine had to be tuned for a higher octane. I figured maybe that an O/B would automatically adjust for the slightly higher octane. Let's see if someone else confirms what you are saying. Unless of course, you a certified O/B technician, then of course your comment of no benefit without tuning it would be on the money.

So the question is out there again for confirmation: if I move up to 91 octane on my 40 hp 4 stroke Merc do I need to tune it for the higher grade or will it adjust for that iteslf. Or should I just stay with 87 regular grade since Merc says "minimum"? They don't say anything about moving higher for more benefit.

Another reason I ask is besides better performance and possible longer engine life . . . My Saabs (tow vehicles) use the middle grade anyway and I always fill back up from a boating trip on the way home as the the outlying counties are usally cheaper per gal (sometimes 25 cents a gal cheaper, simply less taxes than Albany county.
So when I swipe the credit card I can top off the car and then top of the boat with the same grade all wih the same gas nozzle on the same credit card transaction

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

Certified Outboard Mechanic no. Degreed Mechanical Engineer and SAE certified fuel injection and electronic ignition tech yes. The only way your 4 stroke outboard is going to compensate for a higher octane gasoline is by adjusting the timing with a Knock sensor tied into the computer to pull the timing back if you start detonating. You dont have one of those on a Mercury outboard. Using better gas won't hurt your engine but it wont give you any more performance. It will just cost you more.

 

[Scott Danforth]

Re: Wow, all these years and I've always used regular gas . . .

yes the engine will need to be tuned to take advantage of the higher octane rating, however around here, moving to premium is moving to ethanol free, so the benefit of the higher BTU content and lack of ethanol related problems far outweighs any government subsidized benefit of running 87 octane ethanol blended fuel.

your mid-grade will be a blend between your low-grade and premium in most stations. so, if you have E10 low grade and E0 premium, your mid grade will be about E5

will a carburetor equipped engine benefit from higher octane - only from the increased BTU's of the fuel and the proper A/F ratio of pure fuel vs E-blends (not from the octane itself - unless you increase timing) will an EFI engine - yes, from both increased timing and increased BTU of the fuel. too bad marine EFI systems were not closed loop with wide-band O2 sensors.

 

[redjmp]

Re: Wow, all these years and I've always used regular gas . . .

My understanding is that there is in fact less power available in higher octane gasolines not more btu's.
Assuming no ethanol, the higher octane rating is gotten by putting additives in regular 87 to reduce the burn rate.
This in fact dilutes the fuel giving you less gasoline and more additives that don't have any btu's on their own and that don't necessarily burn as clean as good old regular.

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

Depends where you are. In Oregon I can get premium 92 octane pure gasoline all day at half the gas stations in town. I can also get 92 octane E10 at the other half so premium only sometimes means real gas. If I go across the river into Washington I can't find real gas to save my life. I'm somewhat torn on the E10 versus real gas debate though. Yes, real gas does not absorb water like E10 does but E10 will also not allow water to pool in my tank after the stern of my boat get swamped and the vent drinks water. Last couple of tanks of gas of the year I'll use real gas so it stores better in the winter but rest of the summer I use 87 octane like Mercury suggests. The 225 drinks it fast enough so that I dont have to worry about watery old gas breaking down.

yes the engine will need to be tuned to take advantage of the higher octane rating, however around here, moving to premium is moving to ethanol free, so the benefit of the higher BTU content and lack of ethanol related problems far outweighs any government subsidized benefit of running 87 octane ethanol blended fuel.

your mid-grade will be a blend between your low-grade and premium in most stations. so, if you have E10 low grade and E0 premium, your mid grade will be about E5

will a carburetor equipped engine benefit from higher octane - only from the increased BTU's of the fuel and the proper A/F ratio of pure fuel vs E-blends (not from the octane itself - unless you increase timing) will an EFI engine - yes, from both increased timing and increased BTU of the fuel. too bad marine EFI systems were not closed loop with wide-band O2 sensors.

 

[Expidia]

Re: Wow, all these years and I've always used regular gas . . .

Thanks posters for the info. And thx to wired 247 for your backround info. I'm a doubter when people post stuf on the net or even writing and article in a newspaper or magazine. My first thought is "what is their expertise?" Think I'll stick with the 87 regular octane, since it is of since as you say there is no real benefit to my engine without special tuning. That is what I've always believed anyway.

Some posters mentioned Ethanol. A friend asked me just yesterday whats Ethanol is made from, since he has an E85 vehicle. I thought it was just corn. But the answer I read was any starch crop and also certain trees and grasses. What I was surprised to find out though is when you use like E85 or similar you actually see the same performance as straight gasoline, but a big drop in mileage per gallon like in the 25-30% range. That was a surprise to me.

Excerpt:
Performance. No noticeable difference in vehicle performance when E85 is used.
MPG. FFVs operating on E85 usually experience a 25–30% drop in miles per gallon due to ethanol’s lower energy content.
http://www.fueleconomy.gov/feg/ethanol.shtml

 

[wired247]

Re: Wow, all these years and I've always used regular gas . . .

Ethanol can be made from cellulose or switch grass etc especially in the near future when a new variety of enzyme comes into play and makes grasses more feasible in the starch to sugar conversion . Right now its predominantly corn that ethanol is made from in the US which is a stupid waste of a food source. Without subsidies and requirements to use ethanol it wouldnt be practical at all to use ethanol as a gasoline additive. E10 is just plain stupid. E85 is even more stupid but at least you can jack the compression and jetting on an E85 motor and run a balls out race car with it.

 

[Expidia]

Re: Wow, all these years and I've always used regular gas . . .

Ethanol can be made from cellulose or switch grass etc especially in the near future when a new variety of enzyme comes into play and makes grasses more feasible in the starch to sugar conversion . Right now its predominantly corn that ethanol is made from in the US which is a stupid waste of a food source. Without subsidies and requirements to use ethanol it wouldnt be practical at all to use ethanol as a gasoline additive. E10 is just plain stupid. E85 is even more stupid but at least you can jack the compression and jetting on an E85 motor and run a balls out race car with it.

That was always my take on it too! Makes the tree huggers happy, yet mashing all that corn seems a huge waste to me as it could be feeding the hungry all over the globe . . . Just my opinion

 

[ripperace]

Re: Wow, all these years and I've always used regular gas . . .

I thought I'd chime in since the discussion turned towards the ethanol debate. DON'T USE IT! I live in Ohio, and you'll be hard pressed to find a street station that sells ethanol free fuel. I have a test kit that will measure the amount of that crap in the fuel we get. In Ohio, there really is no regulation as how much goes into pump gas. So with that in mind, I've measured anywhere from 4% up to and including 35%, right out of the pump at various places! Now I don't know if most people know this or not, but a lot of manufacturers WILL NOT warrant problems if they discover more than 10% ethanol in your tank if the vehicle or piece of equipment wasn't designed to run it. I have a Harley that STRICTLY prohibits more than 10%. Imagine my surprise when I pulled a test of 13% in my tank! The local marinas are about the ONLY places you can find ethanol free fuel. It's 90 octane, and called "recreation fuel." They HAVE TO run rec fuel, or else their tanks get contaminated with water!

The reason we don't see many issues with ethanol laced fuels in cars is because, generally speaking, autos run a sealed fuel system, whereas outboards, sterndrives, lawn and garden, motorcycles, and most small engines run vented systems. I have a boat that a customer of mine brought to me to work on, and the thing has a hard start problem. I pulled the bowl drains and out comes powder blue colored fuel.....Water contamination was apparent. So I pumped some out of his tank into a clear glass flask. Almost immediately, the fuel started to separate. It had about 30% water in the tank! I know he's running street gas, and he refuses to by the "marina gas" because it's more expensive. Long story short, he's going to end up paying me more to fix this issue that he would if he'd just pony up for the better gas.

And higher octane DOESN'T necessarily mean there's less ethanol. On the contrary, they use ethanol as an octane enhancer. With that in mind, most of the tests I've pulled that register higher were actually higher octane fuel. Now here's the really great part. Ethanol sucks as a fuel. Someone has already stated that it's energy potential is around 25 to25% less than regular petroleum based fuel. That much is certain. It also costs more to refine the stuff to make useable ethanol than it would be to just refine oil, and we'd be further ahead. So you'd figure you'd pay more for the ethanol enhanced stuff correct? Not in Ohio! Here, "rec fuel" is around $5 a gallon from the marina. I know they're paying around $4.11 a gallon for it. Now pull up to a gas station and fill your tank. You're still paying almost $4 a gallon. They get you coming or going. No matter what, they are making you pay for ethanol whether you like it or not. You're getting charged MORE for stuff that actually COSTS LESS to produce, and is better for your equipment!

Ethanol is also a very aggressive solvent. It eats rubber, viton, fiberglass, damn near anything it touches will have been affected with constant use of ethanol. I've seen it eat through an old fiberglass fuel tank, swell viton rubber float needles, shrink cork gaskets, and destroy regular rubber gaskets. It's NO GOOD! If you insist on running it, or have no other option but to run it, be prepared to pony up for fuel system repairs at some time. It's inevitable. I tell my customers to pay me now, or pay me later, because eventually they're going to pay me regardless. Most don't want to hear it, or don't like to hear it. Some will say "I've never had any issues", then come back in a couple months with a fuel system issue.

What can you do if you HAVE no option but to run it? Water separating fuel filters for starters. Keeping your vents to the fuel tanks plugged when stored outside, StarTron seems to help, but once you get water in it, and it separates, there is NOTHING you can do but empty it back out and get fresh. I've had street gas turn in about 2 weeks time. This is NO BS!

OK Rant over for now.....

Ripper

 

[Scott Danforth]

Re: Wow, all these years and I've always used regular gas . . .

My understanding is that there is in fact less power available in higher octane gasolines not more btu's.
Assuming no ethanol, the higher octane rating is gotten by putting additives in regular 87 to reduce the burn rate.
This in fact dilutes the fuel giving you less gasoline and more additives that don't have any btu's on their own and that don't necessarily burn as clean as good old regular.

the various grades of fuel are distilled differently. not by adding carp to carpy fuel.

plus, your "regular" gas is E10 which is 10 percent ethanol is not good old regular, however a crappy blend of government subsidized corn-based ethanol and gasoline. Corn Ethanol has 66% the BTU content of pure 87 octane fuel. 1 gallon of Corn Ethanol has 76,100 BTU's of energy. pure gasoline has 114,100 BTU's of energy so your E10 delivers a maximum of 110,300 BTU's per gallon. not to mention that your car is tuned for pure fuel unless you have a flex fuel vehicle. since your car is not tuned, take another 3% derate on power per every 10% of ethanol for the improper air-fuel ratio.

therefore yes, premium 0 ethanol fuel has more BTU's per gallon than E10

now couple that with the fact that Ethanol doesnt have the carbon backbone for stability and starts to break down in 30 days, where pure fuel will break down after 6 months. tell me what you want in your tank.

I have no problem with Ethanol in a properly tuned engine. the alcohol lowers the combustion temp, and when coupled with forced induction, really big injectors, and proper tuning, it will make a bunch of power (while consuming a bunch of fuel). I just have a problem with government mandated E10 and the problems it has on the marine and small engine markets.

 

[awehnert4]

Re: Wow, all these years and I've always used regular gas . . .

Guys,

Thanks for all these comments to read. I've always used premium fuel in my boat, and until reading this thread did not know it was (clean) or so I thought. Last tank I put in some Stabile additive because I thought ethanol was in the premium also. Just ran a thread called Green fuel, because I had trouble keeping my motor running today after rebuilding it. After several starts and stops, I checked the fuel line at the filter and found my gas was green. Stabile is red and fuel is light golden colored. I don't know if the chemical reaction turned it green, but I think this very strange. Any thoughts?

 

[Pessemist]

Re: Wow, all these years and I've always used regular gas . . .

Typically higher compression engines require higher octane fuels. The reason is to prevent premature detonation of the fuel (knocking) from the heat of compression which can damage engine components.

Higher octane gas actually has LESS energy per unit volume than lower octane gas. It is diluted with components that make it higher octane but take a bit away from the energy per unit.

Performance engine get their performance boost from the higher compression levels--not the use of higher octane fuels.

The higher octane is only necessary to deter the premature detonation of the air/gas mixture in the cylinder.

So for best gas mileage use the lowest octane your engine can run on without knocking. Note that modern computer controlled cars have a 'knock' sensor in them and will automatically retard the timing until knocking is not detected--with a lower performance as a result. So go with the octane level your engine manual manual suggests.

 

[Silvertip]

Re: Wow, all these years and I've always used regular gas . . .

Thanks posters for the info. And thx to wired 247 for your backround info. I'm a doubter when people post stuf on the net or even writing and article in a newspaper or magazine. My first thought is "what is their expertise?" Think I'll stick with the 87 regular octane, since it is of since as you say there is no real benefit to my engine without special tuning. That is what I've always believed anyway.

Some posters mentioned Ethanol. A friend asked me just yesterday whats Ethanol is made from, since he has an E85 vehicle. I thought it was just corn. But the answer I read was any starch crop and also certain trees and grasses. What I was surprised to find out though is when you use like E85 or similar you actually see the same performance as straight gasoline, but a big drop in mileage per gallon like in the 25-30% range. That was a surprise to me.

Excerpt:
Performance. No noticeable difference in vehicle performance when E85 is used.
MPG. FFVs operating on E85 usually experience a 25–30% drop in miles per gallon due to ethanol’s lower energy content.
http://www.fueleconomy.gov/feg/ethanol.shtml

That is hogwash and I now have 74,000+ miles on my E85 capable car to prove it. This vehicle get 30 - 31 MPG using regular fuel (which in Minnesota is E10) on the highway. My "test trip" is always a 430 - 500 miles round trip. That vehicle using E85 does indeed perform better on E85 since it is 104 octane. That performance increase happens because the engine management system can adjust timing accordingly. The 25 - 35% drop in economy is the hogwash part. That same trip produces 27.5 MPG when E85 is used and that represents about a 15% reduction in economy. That same vehicle in purely slow city traffic will rarely fall below 23 MPG. I use E85 anytime the price difference is 40 cents/gallon. Here in Minnesota the more expensive regular fuel becomes, the bigger the spread between the price of it and E85 so my car sees a fairly regular diet of E85 and it has not exhibited one fuel related issue. We have two ethanol plants within just a few miles of where I live so E85 cost is a benefit for me. In many areas E85 is more expensive than regular. But then the misunderstanding about this "alternative" fuel is that it has never been touted as the end-all. It is, after all, an alternative.