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From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Unleaded Regular In The Diesel Tank
Date: Mon, 13 Dec 2004 00:50:29 -0500
Message-ID: <>

On 12 Dec 2004 03:48:05 -0800, "Tom" <> wrote:

>This story is, you understand, only hypothetical. A person would have
>to be a complete fool to do something like what I'm about to
>Let's say that a tired Class 'A' RV driver fueled up in Kingman,
>Arizona. He put about 45 gallons of fuel into his diesel tank. As it
>was well past dark, he decided to pull over for the night. He fired up
>his diesel powered generator for a couple of hours, watched a little
>TV, read the days paper and turned in for the night. He got up the next
>morning and finished his drive into Las Vegas.

Heh.  Just to make you feel a little better, people do it the other way
too.  I was in line to get gas down in Ga a couple of weeks ago.  I
watched the lady in front of me turn on the diesel hose on the combo
gas/diesel pump and struggle for several minutes trying to get the nozzle
in the tank hole.  When she finally decided to just hold it against the
barrier and pull the trigger, I stuck my head out the window to suggest
she might want to think twice about pumping diesel into her car.  A slap
of the forehead and a very red face later, she managed to get the gas pump
turned on...

Anyway, this is what I'd do in that situation.  You've already run both
engines for a period of time so any damage that was going to be done
probably already has been.  Probably won't be any.  Injector pumps
designed to run with low sulfur fuel will probably not be damaged by
diluted gasoline.

I'd dump in a couple of can of your favorite diesel lube enhancer and fill
the tank to the top with diesel and go.  If the engine runs OK then you
don't need to do anything more.  If the engine still runs badly (I'd not
worry about a little black smoke) then it's time to get the tank pumped.

Whatever you do, forgodsakes, DON'T do what several people have suggested
and violate your rig with motor oil or, gad, transmission fluid in the
tank.  Even the low ash formulations now being blended for motor oil still
have a number of additives that will foul your injectors.  Not to mention
ATF which is never intended to be burned and thus contains a variety of
additives that leave ash.  Burning oil that got to the chamber via the
rings is one thing. Burning it through the injectors is quite another.

Dumping your favorite miracle goop in the tank might not have done any
harm back when there was a single hole in the injector that you could
stick a toothpick through.  These days, with the injector nozzle
containing many holes, each smaller than a hair, this magic slop can screw
up an injector in an amazingly short time.


From: John De Armond
Newsgroups: rec.outdoors.rv-travel
Subject: Re: Unleaded Regular In The Diesel Tank
Date: Sat, 18 Dec 2004 06:13:47 -0500
Message-ID: <>

On 18 Dec 2004 00:42:25 -0800, "Tom" <> wrote:

>but It's running ok now. I'm going to take
>the rig down to Phoenix this weekend. On Monday I'm going to get the
>engine and generator oil changed (and all the filters too). As
>suggested, I'll have an old-oil sample taken and analized, just to see
>what's going on there. I'm going to keep adding extra lube additive to
>the fuel for awhile.

Unless it's just time to change the oil, there is no need to.  There is
little to no path for fuel to get to the oil unless you have some sort of
serious problem that keeps cylinder(s) from firing.  Quite different than
a gas engine.

Your engines smoked because the octane improves slow down the precursor
reactions in the newly injected fuel that preceeds the bulk combustion.
The design of the modern diesel cylinder head and injector is to start
burning upon the leading edge of the injection.  In fact some (I know for
a fact Ford is) designs do a little pre-injection event that gets a kernel
of flame started before the main event happens.  That's one of the major
design changes made to quiet the diesel rattle.

When ignition is delayed, fuel has an opportunity to swirl over close to
cold surfaces such as the cylinder walls where it burns poorly.  This
results in soot even though the overall mixture isn't off much and usually
in the lean direction.  There isn't a massive washing of cylinder walls
like happens with a gas engine that sooting.

Something else to consider, the root reason that I recommended you do
little more than put in some additive, and that was mostly for the
feel-good effect.

Gasoline's lubricity has been greatly improved via additives in the last
20 years or so.  The reason is the same as for diesels.  The almost
exclusive adoption of port fuel injection means that injectors with
similar tolerance levels to diesel injectors have to run and survive in
the stuff.  And do so for at least the 100kmile emissions warranty.  The
high pressure isn't there but the tolerances are similar.  A gas injector
operates MANY more times per mile than a diesel.  The engine turns nearly
twice as fast for a given speed, for one reason.  The other is that the
injector fires once a revolution, injecting half the fuel load each time.
There are exceptions, where the timing is linked to the intake valve
motion but that is rare.  Sequential injection is used where the
engine/chassis combo needs every bit of help available to pass emissions.

If you think about it when you get some gas on your hands, it is obvious.
Back in the "good old days" gas would degrease anything it touched, turn
your skin white from the oil depletion and not leave a gooey film.  Today
it feels somewhat slick and leaves a slimy film when it evaporates.  It
doesn't even turn your skin white anymore.

I had my memory refreshed on this back in the summer when they dug up the
tanks for the old gas station across the street.  One tank had about 400
gallons of hi-test still in it.  Having been sealed up for 40+ years, the
gas was in very good condition.  Aaahhh, the smell.  It brought back soooo
many old memories.  It was NOT the smell of "old gas"! Totally non-greasy.
If there hadn't been some water in the tank with the gas, I'd have grabbed
a couple of drums full.

Anyway, if it were my rig, I'd change the filters and leave everything
else alone.  Unless it's time for an oil change.  I realized that there is
a small but finite risk of a negative outcome anytime you open up a
mechanical device.  I think I started realizing that shortly after the
d*ckhead at the quick change place stripped the oil drain plug on my brand
new 280Z!

>Of course, I can't be sure of the results of all of this for the long
>term. For your amusment and edification, I'll post periodic updates on
>this situation. At this time, it would appear that it has cost us about
>20 dollars in extra additive and next week it will cost us the price of
>oil and oil/fuel filters on the engine and generator. That's a pretty
>cheap way out (at this time), when one considers the worse case senario
>after one adds about 45 gallons of unleaded to his diesel fuel tank.
>Again, my sincerest thanks to all of you who offered your advice on
>this topic..

You be welcome.  What amazed me is that with all the respondents and all
the different opinions, no one went ad hominem and no one injected
politics.  Maybe there is hope.  Or maybe I just have all the offenders
killfiled now :-)


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