89 Octane

[Rocky Lou]

My twin Yamaha 300s call for 89 Octane which is non-existent at any of the Marina Gas Docks that I can visit. I can't see myself pouring in expensive Octane Booster on a regular basis. I'm planning to buy a 15 Gallon portable tank (~$100) and wheel it to the boat. If I fill with 87 O, then routinely drop in 15 Gallons of 91 O, from a station, that should keep it pretty close I think. The marina gas is about $1 more per gallon than stations, so I will pay off the portable tank purchase in short order. I am going with 15G since, if one gallon weighs 6 lbs., that's about the most I can comfortably lift into my trunk. Make sense? Any one else have solutions to this issue?

 

[knotflying]

See how the engine runs with the lower octane. If you don't get knocking then why bother. Worth the try.

 

[Rocky Lou]

When I called Yamaha Tech Support, they said pretty much the same thing, but in a unclear manner, and with a comment that other manufactures do the same. The conversation started with their confirmation that my engines are on the list requiring 89 Octane. The 425s have similar requirements, which is unfortunate since the boats with larger engines are most likely to not be trailerable. If outboards are going to scale to larger boats, the manufactures need to consider haul out servicing, currently not searchable on websites, and gas availability.

 

[HookedUp]

I put a 250 on my current boat due to the lack of 89 for a 300. Two things I can't find within 20 miles of my marina: non-ethanol gas and 89 octane gas. I figure 87 octane with ethanol isn't 87 a month or two later. I lost an inboard a few years back to to low octane fuel .... that occurred after the gas aged while it wasn't being used due to maintenance on the other engine!

So, unless I could run non-ethanol or find 89 I don't want an engine that needs 89. Also, I found this on the web.

Using a lower octane fuel than required can cause the engine to run poorly and can damage the engine. It may also void your warranty.

I know lots of boaters near me use 87 in their 300+ engines. I figured if I tried I'd be the one to be sorry.

 

[Familyguy]

All,
First thing is that the HP has nothing to do with the Octane required for an engine. Octane is a measurement of a gasoline’s ability to resist self ignition during the compression cycle in the engine. There are all sorts of electronics on engines now with anti-knock sensors/variable timing etc however, in general, the higher the compression the engine, the higher the octane needed.The manufacturer will tell you in the manual what grade (Octane) of gasoline to use. If you use a lower Octane than suggested the engine will knock under heavier load (like getting up on plain) but you will not hear it because of all the other noises you hear while on the move.
When an engine knocks, this means that the fuel is not being ignited by the spark plug but by the heat of compression so the piston is still on its way up when this happens, and don’t forget that it is the crankshaft that is forcing the piston up and the fact that the fuel has ignited is not going to change the direction of travel of the piston, so now you have an explosion which creates a large amount of combustion gas AND the piston is still traveling up to compress the mixture. VERY hard on the engine!
I am surprised that your marina’s don’t sell at least 89 so I would double check with them (I’m in Canada and all the marinas I’ve come across only sell higher octane fuel). That being said I gotta say that if you have the coin to buy a boat with 70K worth of engines hanging off the back I would not be sweating buying some octane booster, after all the acronym for BOAT in ‘Bring On Another Thousand’ 😀

 

[Rocky Lou]

https://www.amazon.com/Klotz-Higher...la-404766634279&ref=&adgrpid=61941536837&th=1

Klotz Otane booster seems to be one of the better choices. However, I won't be using it since you can do serious damage to fiberglass from spilling. It may not happen the first or tenth time, but, eventually it will.

 

[Matty]

I looked at the reviews for some of the 15-20 gallon portables and did not like what I saw. Instead I bought three 5 gallon cans ar Home Depot for a lot less. They have the handle on top and side and easy spout. Very easy to lift and pour. I did this mainly because I pass the gas station often enough that I fill them easily and I get my money back after about 3 times. My belief is if you keep it at least half full and then had to fill up at a marina on a longer trip that only had 87 you would not have an issue or could use additive that time.

 

[BB marine]

I don't own a 300 hp Yamaha but if I did my concerns would be more about ethanol free gas then octane. Yamaha RECOMENDS 89 octane for the 300 hp big bore 4.2L but not the 250 hp big bore 4.2L. Same basic engine different mapping. Yamaha recommends the 89 octane because using it will allow the engine to reach full designed performance. The 87 octane used in the 300hp under high load conditions may cause the ECM to slightly reduce timing and slightly increase fuel until combustion chamber conditions stabilize. The engine will not be damaged just slightly loose performance. So when no or Low ethanol (under 10% or lower) and 89 octane gas is available Yamaha recommends using it. If 89 octane low or no ethanol gas is not available the use of 87 octane low or no ethanol could be used but with a slight reduction in power. I would be CAREFULL when mixing pump gas from the street and pump gas from the marinas. It is getting harder and harder to find 10% or lower ethanol gas at the street gas station. Even harder to find 89 octane with less the 10% ethanol . If I had a 300 hp Yamaha and the marinas where I boat do not sell 89 or 93 octane fuel and all that is available is 87 octane I would find a gas station that sells low or no ethanol 93 octane gas and mix it with the 87 octane fuel from the marina (if the marina will let you fuel from the dock many don't)This is an effective way of blending gas to achieve close to 89 octane. Better then Octane boosters ( my opinion). If your cruising you will find that some marinas may not sell 89 or 93 octane. You can still fill up and use the engine under normal conditions and loads without damage and may not even notice a difference in performance as long as you have the engine set up properly for the boat. What I'm referring to is make sure your propped correctly. If you have your Yamaha 300hp set up to turn 6000 rpm WOT or close to that with your normal load the way you boat (My opinion) is you probably will not see much difference in performance using the 87 octane. The manufacturer knows that many people don't do this and want to make sure their engines perform properly, efficiently and reliably and maintain proper emissions. The most important part of selecting fuel for reliability is making sure the ethanol blend is at a minimum or none I believe that is more important than 89 octane. I'm not saying just run 87 octane in your 300hp. Yamaha RECOMMENDS 89. I'm just posting my opinion 87 octane can be used if 89 octane is not available if you boat motor combination are set up properly.

 

[Rocky Lou]

Very helpful comments:
@ Matty: I've relied on 'Jerry Cans' for years, but, am no longer able to easily lug 4 at a whack. I'm going to try the cheapo $100 14Gal unit. I also read the -ve reviews...it's not a quality product. There are limits on what you can legally carry in your vehicle...certainly over 20Gal is a problem in most states. I also have to worry about the looks I get when I drive my Tesla into the gas station :shock: :lol:

@ Brian: thanks for providing those details and recommendations. I'll pay close attention to what the pump says about ethanol in both stations and marina. The 91+ blend method also seems best to me. I've read folks doing serious damage pouring octane booster.

~Paul