I recently received this email from a reader:
I have a 6 HP Tohatsu outboard. I have been looking for an in-line water separator for some time. All I could find were for larger engines. I would be even happier if I could find one for a funnel as I store gas in regular cans also and then could just put it through the filter when filling the boat. Does anyone know of a simple water filter?
There are several different types of fuel filters for outboards. The simplest are the in-line filters designed to be inserted in the fuel line. They are usually clear. These do a good job or filtering dirt and debris out of the fuel. They aren’t suited for separating the water out of fuel, though. For one thing, their volume isn’t very large and a small volume of water would overload the filter.
Another style of filter, the one I believe you are referring to, consists of a bracket with the fuel inlets and outlets and a spin on filter element similar to an automotive oil filter. The element can easily be unscrewed to empty or replace. These filters are designed to be permanently mounted to the boat and the fuel lines connected to it. These do an excellent job of separating the water from the fuel but are designed for larger outboards.
Your question and about the filter for as funnel is a good one. For years, cruisers headed to Mexico or other remote areas used something called a Baja Filter. This large filter looked like a big aluminum can but did a good job of filtering dirt and water out of the fuel which was often pumped out of rusty 55 gallon drums.
Practical Sailor magazine did a comparison test of these style filters and was surprised to find the less expensive West Marine filter did a better job of filtering water out than the more expensive Baja Filters.
Remember, though, that E-10 or ethanol enhanced gasoline has a tendency to absorb water from the air. When it has absorbed a critical amount of water, the fuel experiences something called “phase separation”. The water and ethanol drop to the bottom of the tank and the bad gas goes to the top.
Once this happens, there is nothing you can do go get the fuel recombined, it has to be disposed of (properly, please!). I’d suggest limiting the amount of fuel put in your boat’s gas tank to what you think you will be using in the next week or so. Check your fuel storage containers for phase separation often.
Hope this helps!