Mid grade gas vs. Regular Fuel

S

Split Decision

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My owners manual for our 2001 328 Four Winns is on the boat. If I recall correctly I believe the manual states "midgrade gas preferred" and I have always tried to put at least 89 octane fuel in. Anybody have any other info on fuel octane requirements for our boat year?

We are heading out on vacation this Friday and heading up Lake Huron (Great Lakes in Ontario, Canada) I need to stop for fuel about have way up to Tobermory. Problem is the normal place I hit for fuel (Port Elgin) due to construction at the marina does not have fuel available and the other closest marina nearby that makes sense for us to stop in at is Kincardine which only sells regular 87 octane fuel. I probably won't have much 89 octane fuel left in our fuel tanks when I arrive in Kincardine so if I fill up there what I would then have is mostly 87 octane in our tanks.

Is it worth considering buying some octane boost stuff for this 87 fill up, or try to find fuel elsewhere of midgrade or would you feel running with 87 octane is absolutely no issue at all? Thoughts?
 
The issue would be pinging of knocking in the engine. I’m not sure if your engine would have the antiknock sensor and could reduce the engine output? Probably others will comment on your question. What engines do you have?
 
We have twin 5.7 litre Volvo Penta 280 hp GSI engines. Boat is 2001 model year with throttle body injection. Not sure if engines have antiknock sensors or if engine electronics can adjust for Premium, mid grade or regular fuel?
 
Normally you adjust the timing to stop the pinging. So you need to research your engines to see if the engine computer does that? The manual should say something about that. Marina's gas is always suspect to the true octane rating and have read articles about various octane rating when testing gas at marinas. So personal I would run with what you got in the tanks, listen for any unusual sounds from the engines and if so back off a little.
 
It may be because gas octane goes down with time. Maybe not too badly where you live but here in the heat of Florida if my engine is spec'd to run on 87 and the gas sits for a month or two, the octane may be down to 86 or 85 and I'm running out of spec fuel.

Roy
 
I can only speak to MerC and my own experience.

MerC recommendation as noted above is 87 or better.

We usually get 89 "ValvTecT" gas at a marina. It's ethanol free 89 with a Stabilizer in it. Boat runs well, but I've also used 87 E10 toted home from Speedway in 5-gallon cans. Ran fine on that, too, but I don't like it unless I'm going to run it out in few weeks or less. For a couple months down time, I want ValvTecT.

If your 5.7 VP's are set up similar to our 5.7 MerC's, then the Knock Sensor is screwed into an elbow on the starboard side block drain.

I think that if any 87 or higher you can find, is clean, fresh and water free, you'll be OK under any scenario. I applaud your being so thoughtful about the fuel! If you aren't comfortable w/out octane booster, by all means use it. Boating's an extravagant passion that ain't cheap. We also have an RV. I buy the cheapest 87 I can find, but add stabilizer/conditioner to every drop. Boat or RV, all that fuel expense is still probably actually the least costly part of the experience.
 
Thanks for the replies. I'm going to check my owners manual this evening when I get to the boat to review what the actual wording is for what the recommended fuel octane should be. To be honest if mid grade was available I would of just filled up with it and been done. We will be loaded up for this approximate 500 mile trip and may be pushing through some waves with the trim tabs down, so that is what has me thinking a little more about this 87 vs 89 octane concern as the engines will be working harder as compared to our normal weekend boating.
 
Forgot to mention stabilizer - jd is absolutely correct, it slows down the octane lowering. I've used stabilizer since even before the advent of ethanol.

Roy
 
Depends on how you drive. Pinging will happen more when under load. The more load, the more pinging. Accelerate gradually and evenly and either run at hull speed or just over planing speed. Getting over the 'hump' is an area of heavy load but you can throttle up slowly to reduce the load.
 
any compression piston 9.5 :1 or higher would require 89 octane,knock sensor will compensate but performance will suffer
 
Just a follow up on this thread. I did look into my owners manual for our twin 5.7 GSI engines regarding what the specific language that was used for fuel recommendations. This is what my owners manual states. " USE ONLY UNLEADED FUEL. Maximum engine performance requires the use of lead-free gasoline with the following minimum or higher octane specification.

Inside the US.: (R+M)/2 (AKI) - 89
Outside the U.S.: (RON) - 93

If fuels with 89 AKI pump posted (93 Ron) octane number or higher are not available, lower octane fuels (minimum 87 AKI {90 RON} octane) can be used. With the use of lower octane fuel, a slight decrease in power can be expected."

So, I think I will continue to buy mid grade fuel where I can, but will run 87 octane when mid grade is not easily available.
 
Increasing octane is actually lowering the explosiveness(burning) inherent in gasoline. It's preventing or lowering the possibility of pre-ignition(pinging). Gasohol is in itself, lowering the burning/explosiveness of the fuel which increases octane.

If I had the option, I would use leaded fuel which helps, among other things, lubricate the valve seats during combustion. and a cheaper way to raise octane and power.
 
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