[Shop-talk] diesel fuel question

[Benjamin Zwissler]

Diesel fuel goes bad over time.  Just like gasoline the fuel is not
stable.  There are ways to test it but to my knowledge it means sending a
sample to a lab.  Besides sludge and solids accumulating there's some green
mold/fungus that grows in it.  They make fuel conditioner with biocide to
make it last longer but a "few years" is longer than any of them would say
they would protect fuel. Your symptom sounds like a plugged fuel filter.
If you don't have a water separator and fuel filter on your tank I'd add
those and change the filter on your tractor.  Get good filters rated for
the lowest particle size you can.  Injector tolerances and tiny and even
very small particles will cause them to fail.  Ag equipment isn't designed
to as tight a tolerance as on-highway because they didn't have to meet the
strict emissions standards as early, but skimping on filter costs will
result in much higher costs in repairs.  On of my favorite lines from some
Triumph shop manuals starts "It is false economy to reuse (some part I
don't remember)"   So paraphrasing... "It is false economy to use cheap
fuel filters on a diesel engine."

Regarding using the old fuel it all depends on how much you want to spend
on filters and repairs versus disposing of the $150 worth of diesel you've
got in the tank.  The rule of thumb is to not have more than six months
supply on hand.   Older engines will be more tolerant of it than later
(last 10-15 years) engines.  That's why the guys that were cooking their
own biodiesel from french fry oil wanted engines from before the 90s.


Ben Zwissler
bjzwissler at gmail.com
812-343-5533
Columbus, IN


On Fri, Apr 24, 2020 at 7:46 AM eric--- via Shop-talk <
shop-talk at autox.team.net> wrote:

> Does anyone know of a way to tell if diesel fuel has gone bad?
>
> Here is my situation.  I have a large diesel fuel tank for my tractors on
> my property (so I don't have to buy 'over the road' diesel.)  The fuel in
> there has been there a few years.
>
> My newest tractor (a small 25hp subcompact) started acting funny.  At full
> throttle, it seems to sputter a little.
>
> Could be a fuel problem, but I would love to test the diesel somehow. Or
> is there a way of looking at the filter on the tractor? Or another test to
> do?
>
> Related follow up, if the fuel is bad, and I have about 50 gals in a 250
> tank.  Can I just add fresh fuel to it, or do I need to drain out all the
> bad first?  What would be a good bad/good ratio to dilute the bad fuel?
>
> Thanks!
>
>
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