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Old     (deltajake)      Join Date: May 2003       08-13-2003, 10:30 PM Reply   
With todays newer engines does it matter? I have a Sanger V210 fuel injected 315HP. It has always ran 91 octane. There was a recent article in USA Today and the manufactures said it made know difference in autos. Are boat motors any different?
Old     (sdboardr99)      Join Date: Aug 2001       08-13-2003, 11:17 PM Reply   
Octane makes a big difference when an engine is designed to run on higher octane fuel. If you have a high compression engine then you need higher octane fuel to prevent knocking, which damages the engine. Using higher octane than specified is a waste of money.

I have a Mercury 350 MAG MPI and I use 87 and it runs great - I also run 87 in my Ford truck since that's what it is designed for.
Old     (superairdawg)      Join Date: May 2003       08-14-2003, 3:52 AM Reply   
Yep, you should be running at least what your engine manual specifies or you run the risk of detonation (knocking). Some marine engines are tweaked for more horsepower, thus requiring higher octane. PCM recommends running 89 octane in the GT 40, for instance.
Old     (vortech347)      Join Date: Aug 2000       08-14-2003, 5:36 AM Reply   
The only thing you need to know is run the octane recommended by the manufacturer and run MAJOR BRAND GASOLINE.

Do not run Costco, Sam's or other non-major brand gas. They buy the fuel from the petroleum companies that the major brands will not buy because it just barely meets specs as gasoline. It can still be sold as gas but will have less heat energy and more contaminants.

Buy Shell, Texaco, Chevron, Exxon, Citgo, etc. The few extra pennies per gallon are not worth risking clogging up a fuel system on a modern fuel injected engine.
Old     (csquared)      Join Date: Jan 2002       08-14-2003, 12:02 PM Reply   
This has been covered in a few other threads that may be worth a search if you are interested but the basics are:

The condition of the engine and how well it is maintained will make a much larger difference in performance than the octane of the fuel.

If you have an injected motor, running a lower octane is not going to hurt it. The knock sensors will retard the timing and prevent engine damage. Performance may suffer, but you won't hurt anything. Carb engines are a different story.

Run some fuel injector cleaner through it just before the next oil change to avoid carbon build up and keep the fuel system clean. Chevron Techron is good stuff. Carbon build up often causes the need for higher octane fuels.

I run 87 octane in a GT-40 with no change in performance, no increase in fuel usage or any other effects. It is $0.10/gallon cheaper and that adds up over a summer. The only noticable difference is the brand of fuel. It runs better on name brand compared to discount, but it is really only noticable at idle.

Bottom line is it is your boat, do what you are most comfortable with.
Old     (vortech347)      Join Date: Aug 2000       08-14-2003, 8:06 PM Reply   

I agree on everything you said except your statement that running lower octane than recommended will not hurt a fuel injected motor. Not all engines out there have knock sensors. Also, a knock sensor has to detect knock before it can retard the timing. Even that small amount of knock can eventually cause damage. And who is to say that your knock sensor will always work perfectly?

My GT-40 engine in my 99 Nauty is very much affected by 87 octane. I ran 87 mistakenly for a season and the engine would suddenly drop 200 rpm for no apparent reason. It took a trip to the dealer and my reading my manual to realize that it was the knock sensor retarding the timing when it detected detonation.

Since I realized my error and have run 89 octane the problem has only occured one time this year and only happened a single time during that session.

I do agree with running some kind of carb cleaner on carburated engines. Since they are not always perfectly tuned like a fuelly motor they can get carbon buildup that will lead to detonation.

Good points on your part but a little presumptuous about knock sensors being on all fuelly engines.

Old    billywest            08-14-2003, 11:52 PM Reply   
go to ( you can download a short video about the Mercruiser engines. I have a Black Scorpion 330 hp and the video says they were designed to run on regular gas. I switched to 87 octane and have noticed no difference in performance, but a much lower Gas bill. The 340 hp motors are designed to run on regular also 87 octane. No ping. No power loss. Just cheaper. Runs great. I have a Sanger V210 also. Im no mechanic but I believe the 315 hp motor is the same 5.7 liter small block I have. Hope the video will help you out.
Old    grantmi1            08-15-2003, 11:45 AM Reply   
Knock sensors and computers are only designed to retard timing so much they do not have indefite adjustment ability so I would run recommended. It just seems silly to try and save the 6 dollar overall difference. I mean we buy $30,000 plus boats and try and save 6$. lol
Old     (ocrider)      Join Date: Dec 2001       08-16-2003, 12:01 AM Reply   

I am curious where you get your information about the quality of gas at Costco, et al. I have friends who work in the gasoline industry who tell me that Costco buys the same gas that Shell, Texaco, Chevron, 76, and others buy. In fact, the same truck goes from Chevron to Costco in his area to deliver gas!

Most gasoline in this country comes from a very small number of refiniries, and I doubt Costco would buy the "leftovers" from the oil companies. The reason they can sell gas at a cheaper price is because of the high volume and the fact that they never have Convenience stores, bathrooms, etc. and not because they buy cheaper gas.

One other piece of info that might be useful is that places like Wal-Mart don't even actually run the gas stations, they rent out the space to larger companies like Tesoro, Murphy, and Sunoco which are some of the largest petroleum refiner-marketers in the United States.

To answer Mike's question, here is some good info on Octane and Engine Knocking.

Another reliable source of info on Octane:

In summary, you should use the Octane the engine manufacturer recommends.

Old     (vortech347)      Join Date: Aug 2000       08-16-2003, 6:38 AM Reply   
Ryan, I got the information from a source on It came from a guy who sells performance products that has done a great deal of research on different brands of fuel. He has done dyno runs and fuel mileage statistics on multiple vehicles to get to his conclusions.

Now it may be true in your area that Costco is buying the same fuel as Chevron but according to this guy,, not all retailers do the same.

I don't really agree with your reasoning on why Costco can sell at a cheaper price. Convenience stores sell their in store products at a very high profit and use gasoline as a loss leader. They also sell a lot of fuel.

Costco may also sell a lot of fuel but they sell all their other products at a lower profit margin. While their overhead may be lower, they still pay the same price for fuel as the other retailers and they, especially, can't take a loss on anything.

As I understand it fuel is not priced like other products where volume purchased affects price. Since all the fuel comes from a few refineries then why would they be willing to adjust their pricing since they are selling all the fuel they make.

Old     (mikeski)      Join Date: Aug 2003       08-16-2003, 10:28 PM Reply   
I work for ChevronTexaco (yes, they are one company now but not all Texaco stations are selling Chevron gas). In an internal memo a few months ago the gas stations were having issues with the microfilters in the gas pumps. Chevron spent a great deal of money to determine the source of the problem was leftover gas from other refineries in the delivery trucks. They instated a cleanout before filling policy and the problems went away. The big three automakers in detroit truck Chevron fuel for their emissions testing (have you heard the advertising?).

I used to buy cheap, now I buy Chevron (most of the time anyway). Run what octane your engine is designed to run, check owners manuals or stickers on the engine if you have doubts. Like the earlier posts mentioned the knock sensors will retard the ignition timing which decreases horsepower and increases fuel consumption. You may actually spend more using the cheap stuff! Most recent FI boats have excellent fuel filtration/seperation systems but that will not make up for low octane.

A couple years ago my buddy raced his M/C early Corvette engine vintage against a newer boat with the exact same engine, transmission and prop. The older boat with over 1000 hours pulled the newer boat. The difference was 87 versus 91 octane fuel.

I buy the expensive stuff and enjoy peak performance. Make your slacker buddies pitch in a few more bucks per tank. Hey, you bought the boat, they should pay for fuel.
Old    sandman            08-18-2003, 10:54 AM Reply   
I have a 96 315HP Mercruiser Black Scorpion and the manual as well as the sticker on my board state 91 octane is required. I'm still trying to figure out the difference between mine and the 97-2003 330HP versions that are specified to run on 87. I have run 89 in mine when 91 was not available and noticed no difference.
Old    prestige            08-18-2003, 12:35 PM Reply   
If you are towing your boat up a lot of hills and you notice your vehicle is knocking and pinging, you may want to switch to a higher octane gas before your next big trip.

We have a 98 Ford Explorer and find that the knocking and pinging goes away with the higher octane gasolines. (I live in BC, Canada with lots of mountain roads)

(I know the posting is about boat gas, but this is applicable for the vehicle towing the boat)

(Message edited by prestige on August 18, 2003)
Old    hippie            08-18-2003, 1:03 PM Reply   
I work in a refinery and can assure you that off brand gas is no different than name brand.For that matter about 5 different brands come from the same tank,the only differance is each brand uses their own brand specific detergent package added at the loading rack.


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