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Mixing last years fuel with this years new spec.

My Narrow boat fuel tank is about 3/4 full with last years old spec fuel.
Would it be better to run it right down before filling up with the new spec fuel, or top it up with new now.
Will the two fuels mix OK or what problems could I expect ?

Asked by: David Spencer  | 11.25am, Wednesday 11 May

WW says:

Hi David,
The fuel will mix fine- they are designed to. My only concern would be that older fuel does tend to degrade over time (especially as it is returned hot from the injector returns) and that most narrowboat fuel tanks get quite hot from the sun, when mounted in the counter.
I would consider topping up with the new fuel, while adding a good-quality fuel improver/stabiliser- this should reduce the effect of any water present in fuel that biodiesel blends might have (which many supplier fuel will contain biofuels).
It would be very worthwhile draining any water/sediment from the base of the fuel tank, before topping up, if you have not done that already this year. Also, might be a good time to change the engine fuel filter (if not done in last 12 to 18 months)- and if you don't have a prefilter/water seperator filter fitted before the engine filter, it might be a good time to do this as well. Then, should any probelms occur (diesel bug, water, in fuel) then you can deal with it, rather than a sudden engine stop!
Back to the original point- mixing the fuels is fine, but I would then run down the tank as low as you dare go, before refilling in the future- which will improve the general condition of the fuel, as well as using a suitable fuel additive, which can help prolong the lubricity/cetane rating of the fuel, and combat water/diesel "bug".

Mark Langley  | 12.21PM, Wednesday 11 May

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