PBO reader Roy Gwilliam wants to know if it’s worth paying extra for the best boat fuel available. Engine expert Stu Davies has this advice…

PBO reader Roy Gwilliam asks: “I have a Yanmar 3YM20 engine in my Dehler 32, built in 2010. I generally use red diesel with the belief that it does not contain bio-fuel therefore reducing the risk of moisture in the fuel and the associated problems with diesel bug. Am I right?

“I treat the fuel with Marine 16 in any case and keep the tank full in the winter. So far I’ve gone six seasons without any problems.

“With regard to fuel itself, is there any benefit to using super-diesel? Would it be better for my engine – e.g. cleaner, quieter, better consumption figures, prolonged engine life – as is suggested for car engines?”

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PBO engine expert Stu Davies replies: “Older style diesel engines will basically run on any type of oil as long as it will pass through the injector pump and injectors.

“Our engines are relatively old fashioned and can, within reason, burn anything from central heating oil through paraffin to red and white diesel, but with caveats that its use can cause damage because of lack of lubricity in paraffin etc.

“In the olden days in the days of the fuel crisis people would use a gallon of paraffin mixed with half a pint of straight 30 sae engine oil!

“Unless it specifically states FAME free (Fatty Acid Methyl Ester) then its a good guess nowadays that red diesel does contain some bio-fuel.

“EU rules originally stated 5% content in normal road diesel and some of our red is the same as that just with the red marker dye in it. The issue that us yachties have is that the FAME can promote the bug in our tanks.

“Using standard road diesel from the supermarket doesn’t help with this, it contains FAME as well.

“Having said all that I used red diesel in my Beneteau for many years before moving to Portugal and Gibraltar. We fill up wherever we can. There is no such thing as red diesel, it is all bog standard road fuel.

“Super diesel will burn cleaner and will shift sooty deposits. According to Autoexpress ‘this more expensive super diesel will feature chemicals in its mixture that are designed to shift soot deposits and other oily build-up from within the engine’s fuel system’.

“So, use whatever you can get basically, continue using Marine 16, that’s what I use, and if you fancy giving it a good blast, fill up with super diesel and give the engine combustion chambers a good cleaning!”

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This article appeared in the January 2022 edition of Practical Boat Owner. For more articles like this, including DIY, money-saving advice, great boat projects, expert tips and ways to improve your boat’s performance, take out a magazine subscription to Britain’s best-selling boating magazine.

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