gas

[mark poulson]

What octane gas do you guys run in your boats?
I'm asking because I just switched from 87 to 91, and saw huge performance gain.

[eagle123777]

87 as per the merc motor book..i am no expert but could 91 burn to hot to hurt your motor if 87 is recommended.

[blkdog812]

non- opti and older motors should be 89 oct.

[mark poulson]

My Merc. authorized mechanic suggested the switch.

[blkdog812]

which motor are you running. the 89 oct recommendation can from the merc field rep. premium has too many added chemicals to get the oct rating that is not good for older outboards

[Nick Gregg]

I recently had my 2001 Mercury 200 EFI rebuilt by our local mercury certified master mechanic, and he scolded me for having not been running premium fuel (91 octane).

[mark poulson]

which motor are you running. the 89 oct recommendation can from the merc field rep. premium has too many added chemicals to get the oct rating that is not good for older outboards

It's a 2007 115 Opti.

[mark poulson]

I recently had my 2001 Mercury 200 EFI rebuilt by our local mercury certified master mechanic, and he scolded me for having not been running premium fuel (91 octane).

My mechanic was shocked when I told him I'd been running 87 octane all these years.
The switch to 91 gave me a real boost in both performance and smoothness. It idles more smoothly, and seems to run more smoothly, too. It may just be wishful thinking when I'm running, since it's kind of noisy, but I know it idles smoother and easier.

[blkdog812]

deleted

[blkdog812]

opti are 87 rated. 89 is better, but 91 is not good for them.

[blkdog812]

opti are 87 rated. but 89 is ok and a little better due to our ca crap gas, but 91 is not good for them.
non-opti and older motors should be running the 89 oct.

[clum553946]

FUEL:
-All models- MAXIMUM ETHANOL CONTENT: 10%. Ethanol content may adversly affect engine performance.
-See "Mercury's View of Ethanol" on Sherm's board at: Mercurys take on Ethanol blended fuel
-Standard Opti's (ALL) 87 Octane MINIMUM.
-Standard 2-stroke Carb/EFI Models: 87 Octane MINIMUM.
-XS, XB or Racing PRIOR to 2006- CONSULT OWNER'S MANUAL! Most require High-Test!
-ProXS and 250XS 2006-later: 87 Octane MINIMUM. Idle quality may improve with 89 Octane (mid-grade).
-300XS- Consult Owner's Manual. High Grade (minimum 91 Octane) fuel required!


This is from Don Weed @ European Marine!

[adamsj13]

What about Yamaha HPDI? What should be ran in those?

[drew]

Running a higher octane pump gas will not hurt any outboard in anyway. The octane number is the rating of the fuels stability or ability to resist knock.

It has no affect on the fuels BTU/Lb or its burn rate. The only downside is the cost. My recommendation is to run a fuel with a few points higher to offset a fuel that is in poor quality or on the low side of the tolerance range.

[scott h]

Running a higher octane pump gas will not hurt any outboard in anyway. The octane number is the rating of the fuels stability or ability to resist knock.

It has no affect on the fuels BTU/Lb or its burn rate. The only downside is the cost. My recommendation is to run a fuel with a few points higher to offset a fuel that is in poor quality or on the low side of the tolerance range.

The other downside to that is higher octane fuels run hotter in outboards, is what I was told by a reputable mechanic and that's why Merc recommends 87 octane.

[Revoke36]

What about Yamaha HPDI? What should be ran in those?

I run 87 since that's what is recommended in the owners manual.

[drew]

Same btu/lb regardless of the octane. If the engine is equiped with a knock sensor it might be able to run more advance with an increase in octane. This could increase output slightly. To say in general that outboards will run hotter is not correct. I'm an engineer with two decades of internal combustion engine development experience. I have also worked as mechanic for 10yrs while I was in college.

Running a higher octane pump gas will not hurt any outboard in anyway. The octane number is the rating of the fuels stability or ability to resist knock.

It has no affect on the fuels BTU/Lb or its burn rate. The only downside is the cost. My recommendation is to run a fuel with a few points higher to offset a fuel that is in poor quality or on the low side of the tolerance range.

The other downside to that is higher octane fuels run hotter in outboards, is what I was told by a reputable mechanic and that's why Merc recommends 87 octane.

[mark poulson]

Same btu/lb regardless of the octane. If the engine is equiped with a knock sensor it might be able to run more advance with an increase in octane. This could increase output slightly. To say in general that outboards will run hotter is not correct. I'm an engineer with two decades of internal combustion engine development experience. I have also worked as mechanic for 10yrs while I was in college.

Running a higher octane pump gas will not hurt any outboard in anyway. The octane number is the rating of the fuels stability or ability to resist knock.

It has no affect on the fuels BTU/Lb or its burn rate. The only downside is the cost. My recommendation is to run a fuel with a few points higher to offset a fuel that is in poor quality or on the low side of the tolerance range.

The other downside to that is higher octane fuels run hotter in outboards, is what I was told by a reputable mechanic and that's why Merc recommends 87 octane.

Drew,
I was told that the ethanol in today's gas begins to reduce octane over a period of time, and, that if I don't use much gas each trip, my gas octane will go down unless I use some kind of fuel stabilizer to combat that.
Has that been your experience?

[drew]

I have not personally had any problems. Although I have heard of more fuel related issues with the alcohol compared to the previous MTBE blend.

Unfortunately the alchohol is responsible for part of the fuels ability to resist knock. So if the alchohol absorbs water or evaporates it will lower the overall performance of the fuel.

Alchohol is not ideal for our application. Many states have non blended gas for marine use. IMO If one did a back to back comparison of blended to non blended they would never run the alchohol blend again.

Drew,
I was told that the ethanol in today's gas begins to reduce octane over a period of time, and, that if I don't use much gas each trip, my gas octane will go down unless I use some kind of fuel stabilizer to combat that.
Has that been your experience?

[JHaley]

I typically run 92 Octane, non-ethanol in my 225 Optimax Pro XS. Did the same with two other Mercury Optimax engines. Never had a problem and pleased with the performance.

[adamsj13]

I typically run 92 Octane, non-ethanol in my 225 Optimax Pro XS. Did the same with two other Mercury Optimax engines. Never had a problem and pleased with the performance.

I dont think NON -Ethanol is available in Crapfornia i mean California

[NoCAL]

You can do a quick Google search for non-ethanol gas in CA. Apparently there are only about 7 stations that sell non-ethanol gas. So even if you are buying premium it does have 10% ethanol in it. The state mandated it with the switch from MTBE.

NoCAL

[blkdog812]

outboards do not have the knock sensors and computer adjusted sensors and timing like a car. run the wrong fuel and see what happens when you lean burn a cylinder......$$$$$$$$$
why do you think the outboard mfg are fighting 15% e fuel. all that extra alcohol will be the death of outboards.
opti are 87 rated. but 89 is ok and a little better due to our ca crap gas, but 91 is not good for them.
non-opti and older motors should be running the 89 oct.

by clum553946
FUEL:
-All models- MAXIMUM ETHANOL CONTENT: 10%. Ethanol content may adversly affect engine performance.
-See "Mercury's View of Ethanol" on Sherm's board at: Mercurys take on Ethanol blended fuel
-Standard Opti's (ALL) 87 Octane MINIMUM.
-Standard 2-stroke Carb/EFI Models: 87 Octane MINIMUM.
-XS, XB or Racing PRIOR to 2006- CONSULT OWNER'S MANUAL! Most require High-Test!
-ProXS and 250XS 2006-later: 87 Octane MINIMUM. Idle quality may improve with 89 Octane (mid-grade).
-300XS- Consult Owner's Manual. High Grade (minimum 91 Octane) fuel required!

[drew]

Some outboards for our application do use knock sensors and most likely all of the future designs will as well. A higher octane with the same basic properties will not hurt an engine.

outboards do not have the knock sensors and computer adjusted sensors and timing like a car. run the wrong fuel and see what happens when you lean burn a cylinder......$$$$$$$$$
why do you think the outboard mfg are fighting 15% e fuel. all that extra alcohol will be the death of outboards.
opti are 87 rated. but 89 is ok and a little better due to our ca crap gas, but 91 is not good for them.
non-opti and older motors should be running the 89 oct.

by clum553946
FUEL:
-All models- MAXIMUM ETHANOL CONTENT: 10%. Ethanol content may adversly affect engine performance.
-See "Mercury's View of Ethanol" on Sherm's board at: Mercurys take on Ethanol blended fuel
-Standard Opti's (ALL) 87 Octane MINIMUM.
-Standard 2-stroke Carb/EFI Models: 87 Octane MINIMUM.
-XS, XB or Racing PRIOR to 2006- CONSULT OWNER'S MANUAL! Most require High-Test!
-ProXS and 250XS 2006-later: 87 Octane MINIMUM. Idle quality may improve with 89 Octane (mid-grade).
-300XS- Consult Owner's Manual. High Grade (minimum 91 Octane) fuel required!

[Terry Smith]

What octane gas do you guys run in your boats?
I'm asking because I just switched from 87 to 91, and saw huge performance gain.

Run what the manufacture suggest. What it sounds like to me is that you have some carbon buildup on your piston tops/ combustion chamber. The higher octain will help make up for A dirty engine. Try running some fuel syetem cleaning additives and you should be able to go back to 87 octaine.

Terry

2004 Opti 87 octaine

[Terry Smith]

91 octaine does NOT burn hotter than 87 octaine it just can withstand more compression before igniting. It burns A little longer which if used in an engine that requires 87 octaine you are just sending still burning fuel out the exhaust sytem which is not good. If you adjust the engine timeing which is normally to advance the timing you can run 91 or higher octaine properly.


Hope this helps understand octaine A little better.

Terry

[drew]

Pump gas has the same btu/lb , burn rate and composition regardless of its rating. It is manufactured to federal standards. There is a tremendous amount of bad information on the web about fuel. To have a good understanding of this topic one would need to have studied organic chemistry and have formal IC engine development training.