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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Ping Alan Robinson (again) Onan
Date: Mon, 30 Jan 2006 00:43:00 -0500
Message-ID: <>

On Sat, 28 Jan 2006 23:25:01 -0800, altar wrote:

>Sorry to bother you again, but.....
>Onan NHE Emerald Spec E  6.5 (387 hours)
>After reading every thing you have written regarding Onan (some 255
>posts), I have come to the conclusion that I have excessive carbon in
>the heads. Beyond pinging. It's knocking a little. Louder with load.
>C3 didn't reduce it. From reading of your posts, it probably needs to
>be taken apart and manually removed. So....
>Two questions:
>1: What should I expect to pay for that procedure?
>2: What happens if I ignore it?
>Thanks to you, otherwise it runs like a top.

Alan can answer the cost question but I bet it'll be high, knowing

My first thought is, that sure is a low hour count for there to be
significant carbon.  Maybe you can find someone with a borescope to
take a look through the sparkplug hole before you proceed.  A
compression check will also disclose the problem.  Compression will be
HIGH with significant carbon.

If the compression is normal and/or the borescope shows a clean
cylinder then there is some other cause.  Advanced timing and lean
running are two typical causes.  lean running can be caused by a loose
intake manifold, a loose vacuum hose, a partially clogged main jet in
the carb or maybe a crack somewhere in the intake.  Certain failure
modes for electronic ignitions can advance the timing.

Another cause of continuous detonation is overheating, usually caused
by something blocking the cooling air.  The power is usually down
significantly when overheating is that bad.  Maybe Allan can tell you
what a typical head temperature is.  Under about 285 deg F, I imagine.
Make sure the cooling air ducts aren't blocked and that the cooling
air isn't cycling back into the air intake.

One check you can make is to feed the genny some premium gas.  If
there is a timing problem, premium will probably make the pinging go
away.  It might make it go away from lean running.  It probably will
not address overheating-induced pinging.

Before you go for the carbon scraping, a couple of suggestions.  In
case you didn't notice the distinctive smell, C3 is nothing more than
high priced, aerosol packaged Marvel Mystery Oil.  Marvel Mystery Oil
is a mixture of mineral oil, Stoddard Solvent and Oil of Wintergreen
plus an unspecified chlorinated hydrocarbon.  It is FAA approved as a
de-carboning agent for piston driven airplane engines.  Some
discussion here:

A gallon of the stuff is cheaper than a single can of the C3.

It will do a remarkable job of de-carboning if given time.  It does
take time and repeated use.   The MMO must be in contact with the
deposits for an extended period.

One method is to choke the engine down with MMO, similar to the C3
instructions.  Saturate the combustion chamber, then let it sit for a
week. Maybe pour some more in through the spark plug holes.  Crank the
engine but don't get it fully warm.  As soon as it's running clean,
repeat the choking procedure.

Another method is to mix MMO with the gasoline.  Hard to do with an RV
generator since the genny gets its fuel from the main gas tank.

Another method is to feed a small amount of MMO into the intake over
an extended period.  The Marvel company used to sell an aux carburetor
that could be fitted over the carb bell of a car engine.  It would
meter in the MMO as the engine ran.  I haven't seen one in years.

If your carb or intake tract has a vacuum connection, you could meter
in the MMO via that port, using a needle valve to control the flow.
Just make sure it can't siphon with the engine off.  Or you could rig
a small 12 volt solenoid to power from the "generator running" light
to gravity feed MMO into the intake when the engine is running.

A continuous feed requires only a small amount.  Just a trace of smoke
in the exhaust should be visible, perhaps not any at all.  If the
exhaust is billowing smoke, you're metering too much.  It won't hurt
anything but it wastes oil plus the residue will slobber all over the
exhaust system and the side of your rig.

With any of these techniques, you can monitor your progress with a
compression test.  The compression will DROP as carbon is removed.

Water admitted in small amounts to the intake of a running engine is
also effective but it takes a long time.  I have a NACA paper in which
the efficacy of water as a de-carboning device was studied for piston
engine aviation use.  The study confirmed what many of us hotrodders
know - water injection works.  You'd have to rig up something to meter
in the water slowly, probably in the same manner as the MMO setup I
described above.  Of the two, MMO will probably be more satisfactory,
as it works faster.

In any event, after you're finished de-carboning, I recommend a couple
of oil changes over short intervals.  Part of the carbon that is
loosened will make it past the rings and into the oil.

If you don't do anything about the problem, it will get worse.
Constant pinging causes overheating, loss of power, damage to the
bearings, potential to collapse the ring lands, sticking the rings,
piston seizure, spark plug insulator breakage and even punching a hole
in the center of the piston in severe cases.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Onan 4C decarboning spray
Date: Thu, 20 Sep 2007 01:16:08 -0400
Message-ID: <>

Following the recent discussion about decarbonizing a generator I decided to do some
research.  I wanted to find out exactly what Onan's "4C" decarboning spray that
they're so proud of (reflected by the price!) contains.  Ergo I requested the MSDS.
Onan doesn't make this available on their website so one has to ask.

I put it on my website to make it conveniently available

The composition is interesting.  Naptha and water account for over 50% of the mix.
2-Butoxyethanol is an emulsifier and coupling agent and Oleic acid (what olive oil
mostly contains) is an emulsifier.  The main active ingredients seem to be water,
Methyl amyl Alcohol and ammonia.  I found a patent, 5433756, that somewhat relates.

This appears to use the water system of decarbonization with some emulsifiers,
dispersants and a catalyst (ammonia).  I certainly can't see anything in the
ingredient list to justify the exorbitant price of 4C.

Incidentally, while searching the patent database I came across patent number
6,673,758 B2 that describes a decarbonization mixture that consists of 50% Wagner
H-121 brake fluid and 50% water, chilled to near freezing.  He was adamant about the
brand name.  Realizing that actually working isn't an essential ingredient of a
modern day patent, this is interesting.  Be interesting to try on a crufty old

Plugging "engine decarbonizer" into the search engine at brings up some interesting results.  I'll be busy
for a few hours going through this list.  Something I've already noticed is that
naptha and water are common ingredients in many of these elixirs.


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