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Dirty Diesel Symptoms

Posted by: Erik Bjornstad

“Dirty diesel” vs. “clean diesel”.  You hear about this term “clean diesel” sometimes.  What are they talking about? If you don’t think you have “clean diesel”, does that mean you have “dirty diesel”? What really are we talking about here?

dirty diesel symptoms“Clean diesel” is more of a catch-all term that’s used to describe changes in both engine technology (like common rail diesel design) and diesel fuel (ultra-low sulfur diesel fuel). Both changes together combine to give us a modern scenario where today’s diesel engines are something on the lines of 99% cleaner than they were 10 or 20 years ago.

“clean diesel” = cleaner diesel fuel + advanced engines + effective emissions controls

What about “dirty diesel”? Is that just the “absence” of clean diesel? Given how cleaner diesel engines and emissions control systems are the dominant technology in use today, dirty diesel is more commonly what you would classify bad diesel fuel as.  What do we mean by “bad” diesel fuel? And since nobody aims to buy dirty diesel fuel, how would you know if you had some or had used some?

When it’s fresh, there’s really no such thing as “dirty” diesel fuel. When you think of dirty diesel fuel, things come to mind like unstable diesel fuel that’s darkened or full of gums and sludge.  Fresh diesel fuel has to meet certain legal specifications for things like water & sediment content. Fresh diesel fuel won’t be dirty.

On the other hand, there’s lots of stored diesel fuel out there. Fuel that’s been sitting in storage tanks for undefined periods of time, being attacked by air and water and microbes, undergoing oxidation reactions and forming varnishes and sludge.  And nobody looks in their tank to check on the condition of the fuel inside. It’s out of sight, out of mind. If you’re in the business long enough or use stored fuel enough times, you’re eventually going to cross paths with dirty diesel fuel.

Symptoms of Dirty Diesel Fuel

Using dirty diesel fuel means the varnish and sludge is going to end up in certain areas of your engine and fuel system. So dirty diesel fuel = injector deposits and clogged filters, among other things.  The outward symptoms of these are pretty straight forward. You’ll get lower fuel efficiency. Hesitation upon acceleration and rough idling. You’ll also get higher levels of certain kinds of emissions, though those will be caught by the emissions control system. So the hesitation, idling and reduced fuel mileage would be the signs you’d be most likely to notice.

What to do about dirty diesel fuel once you’ve used it? The easiest thing to do is use a good multifunction diesel additive with detergency.  How long it would take to resolve the problem depends on how long you’ve been using dirty diesel fuel. But you should expect some marked improvement by the end of the first or second tankful.

You may be interested in these related posts:

How to Choose the Best Diesel Fuel Additive for You

This post was published on September 29, 2016 and was updated on July 9, 2019.

Topics: Diesel