Old diesel fuel

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SimonD

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In the process of buying our next boat - very exciting!

One issue I'd appreciate some advice on: the diesel tank is about half full but she hasn't been used for nearly five years (apart from motoring round from Southsea to Swanwick last August). Is the diesel fit to use? Would it be OK if I just filled the tank to dilute the old fuel, or should I drain it off and start from fresh?

Thanks in advance.
 
The fuel itself will be perfectly OK. I left my diesel VW for seven year when working abroad. It started first time when I returned and ran perfectly thereafter. However, a half full tank may have accumulated condensed water that will lie beneath the fuel. It would be better to drain this off first, if the tank has a drain cock, otherwise draw it out with a Pela.
 
Brilliant, thanks Vyv. I was hoping that was the case. I'm not sure if there's a drain, but I can certainly use my Pela from the top.
 
Vyv, as ever, is right. Petrol does degrade over time, largely through evaporation of the volatiles in the fuel, not present in diesel oil.
However, the likelihood of water condensation is high, an ideal situation for diesel bug to proliferate, if present. As well as draining all water/crud out of the tank and changing the primary filter, a dose of bug-killer would be wise.
 
Draw some up from the bottom corners of the tank or drain some into a jar if you have a drain cock. If it's clean, just get on and use it. If not I would suggest fully draining, filtering and reuse. Make sure you have a couple of spare filters and know how to change them though.
 
Degradation of diesel over time.


There is some discussion on the web about this, and a University of Idaho study is quoted - almost to the exclusion of everything else (which makes me slightly suspicious !) .

http://www.microclean.ws/index.php/microclean-diesel-facts/microclean-diesel-shelf-life


There are a number of other comments from oil companies collected here.

http://axifuel.wordpress.com/what-is-the-average-shelf-life-of-stored-diesel-fuel/


In the OP's position, I'd add bug killer, and then remove the fuel and fine filter it or have it polished, before cleaning the tank and replacing the fuel.

Time-consuming precautions but what are the consequences and costs of a duff tank of diesel ?
 
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The biomuck was introduced in UK diesel oil from about 2010 I believe - in my opinion a nice little scam whereby various pressure groups combine to line their pockets and justify their existence. The vegetable oil suppliers and the oil companies form a nice little cabal with the professional Eurocrats so that the end user has to pay for the muck to be added to perfectly good diesel then we have to pay to buy more gloop to put in to counteract the biomuck. And of course many man/woman hours will have to be spent in standing committee work carrying out monitoring, certification, licensing and reviews etc. And of course no one cares a jot about boat engines which fail off lee shores when the fuel lines and filters clog up. As SimonD's fuel was put in about 5 years ago I suspect it is probably good old fashioned derv which can sit around for years without degradation. Starting with a clean fuel tank is always a good idea so I would decant it, clean the tank and if the fuel is ok use away at it.

Robin
Pleiades of Birdham
MXWQ5
 
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