Octane Rating - 78 - 150HP -Mercury

[aquaholictom]

What grade of fuel should I use in my 150HP Mercury V-6?

Is there any advantage of using higher octane gasoline then is recomended?

 

[fastjeff]

If that's an in-line 6, then all you can get (without ethanol if possible). That's a hot motor!

Jeff

 

[aquaholictom]

It's a V-6 - so there is no reason to burn premium?

I try to avoid ethanol if possible but that's hard to do here in NJ.

 

[galamb]

The (regular) V6's were designed to run on 86/87 octane with up to 10% ethanol.

The ProMax series was designed for 89 octane.

Over 91 octane is not healthy for your motor - to get above that they add a bunch of chemicals (rather than really refine the gas) and some of those are not friendly to outboards.

In general, you should run 86/87 unless you detect some detonation (pinging) and then moving up a bit in octane should help (but so would a tune up in that case).

Ethanol enhanced gas, while bad if it sits for more than a couple weeks, actually gives the gas a better octane rating than it would have without it - so it will burn better/cleaner, but for a shorter period of time than non-enhanced.

I have been running 89 octane, 15% ethanol for the past 2 seasons now (sold locally at the same price as 87 (regular E-10) under a pilot project - E-15 is on the way in the US as well) in my collection of motors (1986 and 1987 OMC's - 2.5 and 140 horse and 1986, 1987 and 1991 Mercs - pair of 9.9's and 15) and have seen zero difference either good or bad.

The 140 is hooked to a Floscan - still burns the same as it did on regular unleaded and 87 octane E-10.

No clogged carbs, no disintigrated seals/o-rings/gaskets etc - but also no additional "gas mileage" with the higher octane - but do notice that if I don't stablize the gas and try to save it for a few days (I mostly throw the days leftover gas in my truck) that I have a somewhat "crappier" idle once the E-15 is 5 or 6 days old - took the E-10 almost two weeks before I started to notice it degrading (even when stablized, which keeps the water from separating out, I do notice the gas still appears to lose octane)...

 

[fastjeff]

A V-6? Then any old stuff.

Jeff