What octane for 2006 Merc Black Scorpion 330HP

[Monkstr6100]

Just wondering what fuel grade i should really be using in my Gekko for my 5.7 black scorpion. Been using premium, but i see some places it says that merc designed it to run on regular 87? And i am lucky that my local gas station sells ethanol free (for extra $) so that is all i have ever ran in my boats. Thanks in advance, Zach

[oldjeep]

87 Octane E10 is what we run in my FIL's Malibu with Black Scorpion. Haven't had any issues with it. I'll spare you the why ethanol isn't really that evil speech ;)

[boarditup]

If you can get ethanol free, that works great to keep water from collecting at the bottom of the tank. If you cannot get it, use blue Sta-Bil frequently to keep everything running well.

[ToddF]

timing, compression and cylinder head chamber design determine the need for higher octane.

Higher octane will help prevent detonation and/or pre ignition, on engines requiring it. Running a higher octane on an engine designed for 87 will just cost more and not do anything for you, unless you make modifications to the engine that require a higher octane.

 

And if your engine is fuel injected or throttle body injected you should run some type of gasoline with detergent, it helps to keep the injectors clean, which is the best way to improve mileage, throttle response and power.

[oldjeep]

@boarditup I think you are confused. If you have water in your tank then with pure gas it will collect on the bottom of the tank. With E10 it will mix a lot of the water with the gas. The secret is to stop putting water in your gas tank. Water only gets in there one way - in the filler neck via either your gas station or water being allowed to pour in.

 

Stabil - won't hurt anything, but also doesn't really do anything. It's 95% Naptha and 5% unicorn tears.

[eleeski]

@oldjeep The primary source of water in aircraft fuel tanks is condensation. We are supposed to keep the tanks full. With that said, rain and leaky gas caps has been the source of any water in my planes. Alcohol dissolves water in fuel but the water can precipitate out as it cools. Not good for flying. I successfully ran a lot of cargas in my 182. That was a while ago and I was never careful to check for alcohol. I have never checked for alcohol in my boat gas. The engine is likely to outlast the hull (too many holes).

Eric

[oldjeep]

@eleeski and in aircraft it makes sense - due to the massive temp fluctuations that you get. In a boat tank, even 95% empty there isn't enough moisture in the air inside the tank to matter or even enough temp variance between the inside and outside of the tank to condense it.

 

[otisg]

I agree with eleeski - I refill my tank after every use and keep it full all winter long to prevent condensation. I also add a mixture of Marine Stabil, will a little Isopropyl alcohol (dry gas) and mystery oil.

Ethanol holds water (condensation) and does not burn off. It does rust the inside of engines.

Isopropyl alcohol (aka rubbing Alcohol) mixes with water and burns it off as propane.

You can also use to help pass the smog emissions inspection on your car...

[oldjeep]

@otisg you must be the only ski guy I've ever heard of with a full tank of gas in a ski boat ;) Guys I ski with seem to like to keep them at 10-15 gallons in the tank max.

 

Doing what you do won't hurt anything, but I've been storing boats, cars, jeeps, streetrods, snowmobiles and a dozen pieces of power equipment with whatever gas they have in them and no additives. We've had E10 for 20 years here and its all I run in everything.

[boarditup]

As a former Coastie and an older boat owner (for a while) I am a bit sensitive about alcohol in the fuel. I've had fuel lines collapse, a tank bottom rust out, rebuilt a carb twice, and run through a few fuel pumps. I've towed in several boats that suffered from water in the tank - most just after the switch to alcohol laden fuels in the area. From my experience, it is worth the extra $50 a season for recreational gasoline and some Sta-Bil. As for octane, match the engine recommendations. Most marine engines are OK even on 85 octane - that is what is available in some parts of the world.

 

My time on the water is very important. I like the boat starting up and running strong every time - even if it sits for a few weeks due to travel. It is just cheap insurance.

[oldjeep]

@boardtip - this is the magic phrase "most just after the switch to alcohol laden fuels in the area."

 

Because E10 cleans out your fuel system, eats old fuel lines that should have been replaced 20 years ago and doesn't work well with all the old in ground tanks that are full of water. We had the same issues in the late 80's when E10 came along, then everyone started maintaining their neglected fuel systems, replaced their leaky storage tanks, and you never hear about fuel related issues.

[eleeski]

@Otsig I'm not sure I follow the recommendation in my plane. Realistically, leaking fuel from full tanks in my hangar is riskier than a trace of water.

Regarding octane, the 182 had more power and got better fuel economy on low octane fuel. It was smoother on a 50 50 mix of 100octane avgas and 87octane cargas.

The old Datsun 2000 needs premium. It pings horribly on regular. But it's an old carbureted high compression sports car engine. Regular was fine at altitude when I lived in the car in Tahoe one winter (I could not afford premium then).

Eric

[DW]

As long as you run fresh fuel and you don't have your Scorpion modified, 87 octane will work fine. Do ensure that the timing is set to specs, or does not advance more than a total of 33 degrees at 3500+ rpm when full advance has kicked in, usually about 8 deg BTDC at idle. The compression ratio on the iron small block 5.7 GM engines is 9.4:1 for most, some variants run 10:1. Fresh 87 octane fuel will work for them.

[madcityskier]

The link says it all for me. All of the mechanics I've spoken to say if you're engine wasn't designed for it, try to avoid it.

 

http://www.planetnautique.com/vb3/archive/index.php/t-18422.html

[oldjeep]

Sure, but any modern engine is designed for it. Mercury says so in their manuals and website and has for years.

 

Mercury has a very good page on their website that covers most of the nonsense that you hear about E10

http://www.mercurymarine.com/service-and-support/storage-and-maintenance/faqs/mercruiser/?category=ethanol#MercEthanol

[madcityskier]

So 15% "must not be used" it risk "serious damage, but 10% will cause no damage? It would make much more sense yo me that it would just take longer for the damage to show up. I'll continue to avoid it as much as I can. Which in my boat is 100% of the time.

[oldjeep]

@madcityskier chances are good that you could run their engines off of 85% as long as the fuel map was able to compensate that far. They are saying that the max they have tested for, accounted for and warranty is a 10% mixture. Same sort of language exists in the owners manual of just about any car you look at (except those certified to use E85).

 

Avoiding it is a choice, which is fine. Around here, it is pretty tough to find non E10 gas unless you know the few stations that carry it.

[A_B]

When i was working through my ECM issue, every Nautique mechanic i talked to said that the new mixed gasoline is killing fuel filters, pumps, etc... Hard to find gas without it though.

I ran mid grade gas for years in my GT10 along with all the other guys i ski with. Several years ago a mechanic told me I was wasting money, We all went to regular and not a ping or knock or drop in performance.

[oldjeep]

not a ping or knock or drop in performance - that is really the secret in terms of octane. In my 3.0L (carb) the manual says 89 and I have to run 91 to keep it from dieseling on shutdown. If you're running what the manual says and not experiencing any signs of octane related issues then there is no reason to use a higher octane.

 

Out of curiosity, how is E10 killing filters and pumps? It will clean all the crap out of your tanks and fuel lines super quick and clog a filter or 2 until your fuel system is clean. Were they seeing long term issues or just the result of the instant cleaning of the fuel systems?

[gsm_peter]

According to my limited knowlege (sorry for language but I do not speak sufficient English):

 

Any modern 4 stroke engine can run on gas or pure alcohol but you need to adjust some things.

- Alcohol has less energy contents. The engine will consume approx 40% more alcohol fuel volume.

- Alcohol has high octan value. That allows for sligetly earlier egnition-spark' and then one will get sligetly higher efficiency and henvce higher hp (around 1%).

- Alcohol (especially Metanol, 'wooden alcohol') is problematic with engine oil.

Mix porly and/or cleans out all grease in the motor and then open for rapid corrosion.

 

Some old out board aluminum castisng (pre 1970 or so) was sensitive to alcohol/water mixes.

I would assume similar applies to older cars.

 

 

Water in the fuel tank.

The humidity in the air in an empty tank is not sufficient to cause problem first night.

BUT the tank is always open and breath in humid air during night and exhale warmer air during day time.

So over a winter condens build up water in the fuel.

Alcohol prevents the water from seaparate from the fuel mix.

 

If (when) the fuel mix has reached the combustion chambers there are no longer a problem.

A waste amount (in this conetext) could then be take care of.

 

 

 

 

[A_B]

oldjeep, they didn't elaborate, only saying they have seen a significant increase in filters and component failure.

 

I really have not had any experience with it, as the stations that I hit on the way to the lake are not adding it. I think the BP stations around here all have a sign noting that they are mixed.

 

Quick lookup by state:

 

http://pure-gas.org/index.jsp

 

 

[madcityskier]

I thought isopropyl was what would help water burn through. Never heard that about ethanol. My brother bought a boat that sat 2 years with e-10. Had to GI through tons of fuel related problems, including the tank emptying itself into the hull through a hole in the fuel line. Could be a coincidence, but it's enough to keep me away from it. My 85 S&S is using it's original fuel line with no issues.

 

[oldjeep]

@madcityskier - some old - and I mean really old fuel line is not ethanol safe. So if you have 15+ year old fuel line, it is a problem (with or without ethanol). Rubber fuel line isn't designed to last 30 years - that is a safety issue regardless of the type of fuel you decide to use.

 

Worse yet is fiberglass tanks, if you have a boat old enough to have those then you never want to put E10 in it.

[Alberto Soares]

Here in Brazil all gasoline are E25, that´s right 25% ethanol. I estimate I probably run about 5000 hours in my last 3 or 4 boats in the last 20 years. The only problem I noticed were with the gas pumps, I would say they last about 1000 hours. My current 2010 Nautique 200/409 has 750 hours on it and is fine so far - I do have the spare pumps, just in case...