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Writer's pictureTom Crosby

Sticky Diesel - Fact or Fiction?

Sticky diesel is causing multiple fuel problems on the UK inland waterways


A massive increase in diesel fuel related breakdowns have been due to sticky diesel.

Article by Darrell Broscomb, Marine Engineer at Tooley’s boatyard in Banbury.

Darren writes that he sees many different mechanical issues throughout the year, but during 2023 notes seeing a massive increase in diesel fuel related breakdowns due to sticky diesel.  At present, the marina had four boats requiring attention because of fuel issues. Diagnosed as not just ‘diesel bug’ but something else entirely.  With this particular sticky diesel scenario, the fuel goes dark, smells different and leaves sticky tar-like deposits in the fuel system.

These issues have been quite challenging to diagnose as the symptoms vary hugely.  Some engines have plumes of white smoke, others vibrate terribly, and others stop running entirely for no apparent reason.

After replacing fuel filters and lift pumps, servicing diesel injectors, and even having injection pumps serviced, the problem can return within a few weeks.  This is very expensive for customers, and us too, as you can’t charge if you’ve been unable to fix anything.

On one boat that had had all of the above done, I bit the bullet and said, ‘Right, let’s get rid of the fuel, clean the tank and replace it with fresh diesel.’  Well, it only worked!  The boat was fixed, and we had a very pleased customer.

So, what exactly is going on then?  We’re fortunate to live in the age of Google, and online searches brought up many articles with similar problems experienced around the country; farmers have been having issues with sticky diesel for a few years now.

Diesel fuel just isn’t keeping well it seems. This is partly because it now has a percentage of biofuel; FAME (fatty acid methyl ester), and the problems seem to be caused by this ‘going off’ in the fuel.

Refineries think that the majority of fuel is used within 18 -24 days of leaving the refinery and state that fuel will perform satisfactorily for 4 to 6 months with the preservatives they use. Unfortunately, this isn’t much help to someone who uses their pleasure craft two or three times a year.  Their fuel could be well over a year old before it is used.

On top of this, modern diesel engines also circulate the fuel through the diesel system to keep components cool and lubricated; the fuel gets heated and cooled during this process and may pass through the system many times before actually being combusted in the engine.  This process changes the structure of the diesel and sees an increase in contaminants in it.  These modern engine fuel systems have very fine tolerances, and the fine injector nozzles can block up.

There has been some research done by Fuel Additive Science Technology (FAST) – which produces Exocet additives. This research has shown that the sticky diesel issue has nothing to do with water, rust or poor storage like the causes of diesel bug; the samples they tested have all had a high particle content. Particles of interest found are sterol glucosides and monoglycerides, and it is these which are causing the sticky deposits; they come from biodiesel, and cold weather separates them from the fuel.

Looking forward, what can we do?

Storage

For a long time, it has been good advice to keep diesel tanks filled to prevent condensation from contaminating the fuel with water.  I’m not sure if this is a good idea anymore unless you use a lot of diesel and will use your fuel in under 6 months. So, ideally, only purchase what you plan to use annually and replace unused fuel before the next season.  Smaller, stainless steel cylindrical storage tanks with bottom drains would be ideal, please boatbuilders.

Treatment

Fuel degrades quickly, so an additive is a good idea; it should include a stabiliser, cetane improver, demulsifier, detergent and a biocide to arrest microbial contamination.  Fuel polishing is a good idea; it seems that fuels with a higher particular content are causing the problems, so polishing (filtering) down to 2 microns could be a suitable treatment.  Fuel polishing is available at many boatyards, or if you are inventive, the parts are readily available to build your own polishing system.

In conclusion, diesel isn’t what it used to be, and without preventative measures, it is unreasonable to expect it to maintain its quality.  Studies have shown that fuel will start degrading within 28 days.

Useful links about the causes of sticky diesel:

 

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