Excessive carbon build-up - 2006 - 250HPDI

[Trioponds]

Just had my powerhead repaired (#3 cylinder blown after only 68 hours) and the technician mentioned that the cylinder and piston were covered with carbon build-up. Powerhead never had anything but ethanol-free 91 octane fuel and Ring Free added every tankful and never run low on oil. Never ran it over 5500 RPMs. Anyone have any idea what might be causing the carbon build-up?

BTW, Jasper refused to make good on their powerhead that had only been run for 7 months and had just 68 hours on it. I'm not at all happy about spending $7k on that and getting hung out to dry by Jasper!!

[CJ1]

What oil you running? Yamaha by chance? I would be trying to get in touch with someone higher up at Jasper if they don't have a good reason for denial of warranty. Cj

[kk4iz]

87 octane is what Yamaha recommends. 91 octane does not run hot enough and will cause carbon buildup. We had over 200 hrs on our 2006 hpdi 250, we ran Seafoam or Ringfree plus Amsoil oil. We just updated to a Sho 250 a few months ago and the old hpdi was still running strong when we sold it

[Trioponds]

CJ1 - Thanks. The reason they denied it was that it was 14 months from when the powerhead was installed (12 month warranty) but the motor sat in winter storage for 7 of the 14 months (Northern NH). They said they wouldn't budge on their decision.

kk4iz - Thanks. The only reason I run 91 is because that is all that is available here in non-ethanol fuel.

[FD209]

I used to run 91 ethanol free also and noticed carbon build up in my exhaust in the hub. After researching it I found a discussion on it in the Mercury forum that stated that the correct octane was more critical than ethanol free. I switched to 87 with ethanol and my carbon problem resolved itself.

[CJ1]

CJ1 - Thanks. The reason they denied it was that it was 14 months from when the powerhead was installed (12 month warranty) but the motor sat in winter storage for 7 of the 14 months (Northern NH). They said they wouldn't budge on their decision.

kk4iz - Thanks. The only reason I run 91 is because that is all that is available here in non-ethanol fuel.

What oil are you running? Cj

[Trioponds]

Yamaha 2-Stroke Oil

[Trioponds]

I had someone else tell me the same thing. I will talk to my technician about it and see what he thinks about that. Thank you.

[CJ1]

Yamaha 2-Stroke Oil

The reason I asked is that is known to be a very dirty oil. Switch to a good full synthetic. Lots of recommendations. I run amsoil. Cj

[kk4iz]

The reason I asked is that is known to be a very dirty oil. Switch to a good full synthetic. Lots of recommendations. I run amsoil. Cj

[yam911]

I used to run 91 ethanol free also and noticed carbon build up in my exhaust in the hub. After researching it I found a discussion on it in the Mercury forum that stated that the correct octane was more critical than ethanol free. I switched to 87 with ethanol and my carbon problem resolved itself.

That is just a forum about Mercury's by a bunch of guys.

Mercury Marine's position is that 92 octane is perfectly acceptable. In fact, Mercury (the company) has stated that given the choice between (a) 92 octane with 0% ethanol and (b) 87 octane with up to 10% ethanol then choice (a) is their recommendation.

From a Mercury owner's manual:

[yam911]

The reason I asked is that is known to be a very dirty oil. Switch to a good full synthetic. Lots of recommendations. I run amsoil. Cj

Agreed. Yamalube is known to result in carbon fouling/buildup. Many that have had such problems have had them miraculously disappear when switching to a full synthtic oil.

[yam911]

Big block HPDI's are known to be somewhat susceptible to detonation. They do not use a knock sensor. The use of gasoline with a higher octane rating is the single most important thing that a big block HPDI owner can do to mitigate the chance of detonation happening.

Carbon buildup can be mitigated and prevented in a number of ways. Much cheaper dealing with carbon buildup than it is in dealing with a hole in a piston.

[CJ1]

That is just a forum about Mercury's by a bunch of guys.

Mercury Marine's position is that 92 octane is perfectly acceptable. In fact, Mercury (the company) has stated that given the choice between (a) 92 octane with 0% ethanol and (b) 87 octane with up to 10% ethanol then choice (a) is their recommendation.

From a Mercury owner's manual:

Yea, I didn't want to get into a discussion about fuels but I always run a higher octane than recommended with no ill effects. Sunoco has a very informative site about fuels and results of operation. I have built quite a few engines and seen the damage from poor fuel. The only ill effects I have seen from a octane rating too high was a strip car actually lost hp. The compression ratio was not high enough to burn the fuel effectively. The perfect octane for a engine is just above the level of detonation. BUT if anything changes guess what, you have a junk piston assembly. So if a HPDI calls for 89 octane and you put 89 in the tank and it is a little old and has lost some of the rating and you run it in a high load condition or you have a injector that is not 100% guess what, you now own a piston [or many] that have a hole or destroyed top and ring. Or it rattles the locating pin out and jams a ring in a port. If you put 93 in it you MAY loose a bit a very tiny bit of horsepower. Personally I would rather be safe than sorry. When I store my boat I will dump a few gallons of 116 non oxy fuel in just to stabilize and guarantee I have good fuel to start the season. I do not run ethanol in anything other than my road vehicles that get used every day. cj

[yam911]

Yep, given the choice between bad stuff happening from gasoline with more than the minimum recommended octane and bad stuff happening from detonation, give me the high octane bad stuff. Much cheaper to deal with than a hole in a piston.

But then Evinrude and Mercury both say there is no bad stuff that is going to happen if one uses gasoline with a higher than minimum recommended octane grade.

What in the heck do the manufacturers know anyway?

[SCOTT196]

I wont run ethanol, no matter the octane! Its junk!!!!! I run amsoil and have no carbon build up in my HPDI.

[Trioponds]

Just returned from an extended vacation. Thank you all for your input. It has been very helpful and informative. My technician agrees with the notion that the Yamaha lube may be the primary cause of the carbon build-up. He feels that, unless the motor is run wide-open most of the time, the higher octane could also contribute to the carbon buildup as well.

[yam911]

Just returned from an extended vacation. Thank you all for your input. It has been very helpful and informative. My technician agrees with the notion that the Yamaha lube may be the primary cause of the carbon build-up. He feels that, unless the motor is run wide-open most of the time, the higher octane could also contribute to the carbon buildup as well.

Did he give any reason why he feels this way?

I don't know of a single automobile or outboard motor maker that provides any cautions or warnings about gasoline with a higher than minimum octane rating in any way contributing to carbon build up.

[lpugh]

Carbon buildup is the reason for the detonation in most cases! Sometime lean mixtures a contributing factor
87 octane always when allowed for by manufacture, synthetic oil or blend always, Top tier fuel (no cheap crap) and allways run a high quality cleaner such as mercury quickean, or chevron techron (black label). Far less carbon, restricted injectors and most likely no detonation issues.
Notice I did not mentions ring free which I have used a lot of, Techron and Quicklean are far better
87 octane burns faster and much cleaner than 91 octane, High quality synthetic oils form a lot less deposits, Top tier fuels such as chevron, Union and even shell will help a great deal in keeping deposit under control and they generally have much better anti knock qualities.
10 percent ethanol or less is not a problem unless you let it sit in the tank for long periods of time, Ethanol is also a very good solvent for breaking down gum & varnish. It also tends to run a little cooler
The only problem with alcohol is when moisture is introduced into the fuel and it is allowed to sit for while, it will cause phase separation allowing the alcohol to mix with the water and drops the lowest areas it can find. Keep in mind the alcohol is the ingredient that boost the octane. When you fire it up you pull that alcohol/water mix first, the rest of the fuel now has a lower octane due to the phase separation. If you are not going to use the boat within a month, you must add a high quality stabilizer (not sea foam)
Top tier fuel I find usually as a lower percentage of alcohol, I have found in my area Chevron being the lowest at 5-6 percent
Also when it separates as described and is concentrated as a result it is extremely corrosive. Without water in the mix and excessive time without use there no issues with a 10% fuel blend
It is far better to run 87 with alcohol than 91 without, Just be aware of what I have posted here and use sensible precautions

I wont go fully into my credentials on this subject, I have many years of experience dealing with alcohol blends and was the first person on the west coast to get a computer controlled carbureted motor to properly function on M-85 (85% methanol-15% gas) or any mix percentage of from 100% gas to 85% alcohol way back in 1985. I learned a lot about it and how to deal with it.

[jp10]

Solid advice, thanks