Mixing Fuel with additives

[S Boring]

I've been around boats all my life, but have only owned my own for the past year. I'm always nervous about making sure the fuel is right so here is my question. When I'm adding something like seafoam and mixing a quart to 6gal does that change the mixture enough to where I need to add a little extra oil or am I just paranoid?



Also I just read a post about making sure of the correct octane to match the motor. I have a 75 merc and have always been on the belief that premium grade was the best to put in a 2 stroke (saws, dirtbikes ect) but with insane fuel costs now is regular just fine?



Also I've not read about anyone using Quicksilver oil. Any opinions on it?



Thanks Bread

 

[Berry Lindley]

I'll take a roundabout stab on the octane. You should use what the engine manufacturer calls for. On my '05 90 HP carbed merc, it calls for national brand mid-grade (91 octane mid-grade) My previous 90hp early 90's vintage only called for 87 octane (regular) so clearly there was an engine design change/fuel requirement change between the time the 2 were manufactured. I have heard that you should not burn premium unless it calls for it. So, you need to find the manual or contact your manufacturer on what to burn in your particular engine. Also a few ounces of seafoam isn't going to much register when mixing oil with the fuel. If you are that worried, deduct that amount from the fuel. Also what is on the Seafoam can is a decarboning treatment, not a regular additive that many people use instead of an annual or semiannual decarboning treatment.

 

[Jim in VA]

Higher octane has a lower flashpoint. Its intended for use in high compression engines where pre-detonation (i.e., explosion caused by compression versus spark - often referred to as "knock" from the sound of the piston being prematurely pushed down) is a problem. It does not provide any benefits in engines not requiring the lower flashpoint to avoid knock. Putting higher octane gas in an engine that does not need it is only burning money out the tailpipe. Stick with what your engine manufacturer recommends. They built the thing after all!! And I highly doubt any manufacturer is going to make operating recommendations on an engine that aren't going to give the engine the best chance of making it through the warranty period without problems.

 

[Rusty C.]

What Jim said!

Bread,

I used to think like you and used the premium gas until the gas prices spiked. I thought I was being good to my engine putting in what I THOUGHT was a better quality fuel. It turns out, it's not about the quality of the fuel, it is about the timing of combustion as Jim said. After talking to Mercury and many experienced mechanics, they all basically said what Jim said. They ALL said your best benefit is to have the engine timing set with reg 87 gas by a experienced mechanic (Mercury's website has a list of mechanics in your area that are Mercury certfied), make sure you have new/clean spark plugs and use seafoam or Quickclean (I prefer seafoam) with every gallon of gas. Another thing that will help you and is very cheap and can do yourself is replace the fuel filter. Also, keep a set of old sparkplugs around to use to decarb your engine. The Mercury/Quicksilver Power Tune decarb spray is the best there is. Use it and watch all of the crap and carbon deposits come out of your engine. It will make your engine run and idle like new. Do this once a year.



As far as the Seafoam is concerned, you don't have to do anything different like less gas, more oil, etc..... Just use one ounce of Seafoam per gallon of gas (I think). I use it in everything I own including lawnmowers, weedeaters, etc.. Not only does it keep gas fresh, it helps keep carbon deposits down.



Quicksilver is owned by Mercury. In fact, Quicksilver is the exact same stuff, they just put it in Quicksilver containers and sell it under a the QS brand to give it a "universal" brand recognition. Many Yamaha or other brand motor owners wouldn't buy Mercury oil, but will buy the Quicksilver brand. See what I am saying? Anyway, all of Mercury products are VERY good quality products.



However, when it comes to engine oil, I prefer AMSoil, hands down. Why? because it is 100% synthetic. It provides much better protection and almost no smoke. It's a win win situation for you and your boat. If there wasn't AMSoil, I would use the Quicksilver/Mercury Premium Plus. It is a sythetic blend. AMSoil also makes a great lower unit oil that is 100% sythetic as well.



I hope this helps!

Rusty