PBO reader Roger Brown wants to know if he should be worried about the orange cloudy diesel in his fuel tanks...

The red diesel in the bowl of my primary filter looks cloudy and has a more orange colour than normal. There is no sign of water in the bowl. I have been treating the diesel with Fuel-Set.

The filter element in the primary filter looks clean and unblocked, but the element in the fine filter (supplied as a genuine Perkins part) has picked up a very fine chalky looking dust.

The engine is running normally, but is it alright to continue using this cloudy diesel? The chalky dust does not seem to settle in the fuel tank and is present when taking a sample from either the top or bottom of the tank.

You will understand I am reluctant to pump out and dispose of the whole content of the tank.

-Roger Brown
Peel, Isle of Man

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The fuel filters on Roger Brown’s yacht have been collecting a chalky white substance from the diesel

Stu Davies responds: “It looks as if you have something in the fuel. Normally the diesel bug produces black deposits and yours are white. This would explain the orange colour, the white contaminant is refracting the light to make the normal red appear orange.

“It could be water? Emulsified and held in suspension by your Fuel Set additive or it could be a solid contaminant. Can you “feel” it?

“I can say that most fuel systems have varying micron size filter components with primary filters normally having a 10 micron size and the secondary nearer the pump 5 micron. It does vary by the way but this is the usual setup.


Stu Davies has a background in engineering in the oil and coal industries

“If it was water then I would expect the primary filter to be collecting it so my thoughts are it is a solid and that seems to be confirmed by your filters. Im afraid it looks like that your tank will have to be drained and the fuel “polished”

“If you want to try and polish it yourself, you can get electric fuel pumps off eBay, you could temporarily jury rig your fuel lines to recirculate your tank through your existing filter system and leave the pump running.

“Make sure you have a few filters and let it run for a day to recirculate the fuel and collect the contaminant.”

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