View Full Version : Fuel Question

09-27-2005, 10:46 AM
Hi guys! I just wanted to pick a few of your brains in regards to fuel quality/octane amounts for my boat. I've got an imboard Kodiac v-6 Vortec engine and also a Merc four stroke 9.9 Big foot kicker. Both are plumbed into the same under floor tank. I've been putting supreme high octane gas in it and was wondering if it is really worth it. Should I continue doing so? Or do you think reg unleaded gas will be o.k.??? I always put Stabilze in it to keep the water out and also a water/fuel seperator filter is hooked up to the inboard. You probably know why I'm asking about the use of cheaper gas. I've got a 41 gal tank (do the math!!). Thanks for any thoughts! ;)

09-27-2005, 11:41 AM
As I was schooled by Doc, if you fish high altitude, you are wasting your money with high octane. Something about less oxygen, air fuel mixture, blah, blah, blah... ??? I just relied on the answer rather than trying to understand the chemistry. ;D

09-27-2005, 12:08 PM
Yep. High test is overkill. Most 4-stroke OB manufactures now recommend 89 octane mid grade fuel from Chevron or other "top tier" brand. Regular grade is better for elevations over ~5,000 ft.

Unfortunately, Chevron or Shell mid-grade usually costs more than other brand's high test.

Using a cheaper brand of fuel and putting 2 bottles of Techron through your tank once a year might be a lower cost alternative. That's what I do with my cars.

09-27-2005, 06:20 PM
I am 100% sure that Doc is right, and always value his opinions, but I just can't break myself from putting in Chevron Supreme. *Maybe it's just preference, but I believe that the Techron additive in Chevron supreme, and the fact that fuel looses 1 or 2 octane points over time, makes it worth putting in the supreme.

I'm not a mechanic any longer (thank God), but I was for many years. *I have taken apart countless engines and fuel injection systems. *I do know that it is easier to keep a new engine and injection system clean, than it is to clean a dirty one.

Besides, since I am going to be making payments on my boat till the day I die, or longer, I want everything to last as long as possible, and be maintence free as possible.

By paying the extra for Chevron supreme, it's possible i'm only buying piece of mind, but it's worth it to me.

If i'm up in altutide I use the mid-grade, and I always add Sta-Bil.

Just one guy's opinion, and you know what they say about opinions....

09-27-2005, 10:03 PM
Thanks guys for the info and your opinions! It's always apreciated. ;)

09-28-2005, 09:28 AM
How about for 2 stroke outboards? Can we throw in a few real names and numbers?

For my 2 stroke used at SEA LEVEL, does it mean I can use either:

1) Chevron or Shell mid-grade (89 octane) gas


2) ARCO high-grade (91 octane) gas plus once-a-year Techron?

09-28-2005, 10:18 AM
Stick to the mid grade stuff. The manufacturers recommend that for 2-strokes as well. You're really just throwing away $0.10 per gallon using 91 octane fuel. But it won't hurt anything. ;D

For 2-strokes, I recommend a once a year treatment with SeaFoam. Wait until you see the amount of carbon and other crap that you'll burn off with the first treatment.