Show of hands...

[willk]

I've been told by several people that letting your tank run dry/nearly dry will suck up water and crap in to your engine. I don't understand how this is supposed to happen?

Boat tanks are well shaken in use, so fine crud will surely go into suspension during use.

Water sinks. Fuel lift pipes end VERY low in the tank. Surely they'll lift any water they touch, irrespective of how much clean/dry fuel is above them?

There is some exceedingly dirty fuel (especially diesel) for sale. Marinas have a poor rep in this regard, but I've received some awful dross from big name suppliers inland too.

Good filters, spare filters and water separators are a must. Diesel bug thrives at the water/fuel interface, so keeping tanks free of water has to be a good idea. Filling your tank in Autumn and adding a treatment can't hurt.

[Crusher]

Originally Posted by willk

I've been told by several people that letting your tank run dry/nearly dry will suck up water and crap in to your engine. I don't understand how this is supposed to happen?

Me too!! I've never understood this theory!!

[lakelandterrier]

I try to leave my 90l SS internal tank about 2/3 full with petrol over winter (Nov-March). Boat kept out of doors, but sheltered between 2 buildings.

My logic is that this should minimise any condensation (but any water should be caught in the separator), and if the fuel does degrade over the winter, this will be diluted by topping up with 30% fresh. Not had any problems with this method (so far).

[Poly]

Originally Posted by willk

There is some exceedingly dirty fuel (especially diesel) for sale.

I'm surprised you have that problem. My friends across the Irish sea tell me its very easy to get "laundered" fuel if you know where to go

[nik]

Originally Posted by Bittentobuggery

can I ask how many times you ran your tank dry ?

As I see it, you could be building up a potential problem without realising it. If there is any water, it will sit in the bottom of the tank and only present itself when you are draining the dregs of the tank.

I really don't understand this argument.
Water will sit at the bottom of the tank.
The fuel pickup pipe will be at or very near the bottom of the tank.
I can't see "how much fuel is in the tank" will affect water being picked up. The fuel pickup height does not change with the level of fuel in the tank.

I totally agree with having a water trap and I can see that keeping the tank full will reduce condensation. But even if you do not keep your tank full and you get condensation, the water trap should take care of it. Assuming you check regurlarly and drain if necessary.

Just to reiterate, I did not bother keeping my tank brimmed, although generally more than half full and I never had a water or bug problem.

[willk]

Originally Posted by Poly

I'm surprised you have that problem. My friends across the Irish sea tell me its very easy to get "laundered" fuel if you know where to go

Your friends can't be local or are hopeless optimists. Unless you know where to go, you'll almost certainly be using it...