After our boat had sat all summer in the heat and humidity of south Florida, we wanted to polish the fuel before putting her back in the water. Although we had left the fuel tanks full, condensation can still occur. And you never know what may have grown in the tanks . . . microbes love water and multiply in it at the bottom of the tank. Biocides can only do so much.
Why and When Polish Your Fuel?
Why worry about water, sludgy microbes and debris? The immediate problem is that your engine will die — it won’t run on water and debris can block the flow of fuel. That’s bad enough if it happens just as you’re entering a tricky place, say a marina or going through a bridge. But the even bigger problem is that both water and debris can cause thousands of dollars of damage to your engine.
IMPORTANT NOTE: Even with a Racor filter on your fuel line, if there is just too much water in the fuel, it can get past the filter on the smaller Racors that most recreational boaters have — large Racor systems sometimes do have a check valve that stops the flow if the water reservoir is full. Always check the sight bowl in your Racor for water at the end of a day; check it several times a day if motoring a long time in order to catch a problem before your engine is damaged. Sludge and debris can clog a Racor in mere hours, again causing your engine to just stop.
Fuel polishing is pumping all the fuel out of your fuel tank(s), running it through a filter to remove water and debris and putting it back in the tank. Some professional services also clean the tank while it’s empty.
When might you need to polish your fuel?
- When your boat has sat for a while in a humid climate (particularly with day/night temperature swings causing heavy dew or fog, both indicators that condensation is likely in the tank)
- A new-to-you boat that hasn’t been used recently.
- Discovering that the fuel cap was loose and water/dirt may have entered the tank.
- Someone confusing the water and fuel fills and putting water in the fuel. Yes, this happens.
- Getting a load of “bad fuel.”
- Discovering an abnormal amount of water or debris in your Racor filter.
- Before going out in “boisterous” conditions if the fuel hasn’t been polished recently — any water and debris that has settled to the bottom of the tank will be stirred up with the motion of the boat.
In many places, there are commercial fuel polishing services. But it always seems that when we need our fuel cleaned, there are none available, they’re prohibitively expensive, or there’s a long wait for service. Hence doing it ourselves (we know some people who have fitted an electrical fuel pump and filtering loop onto the fuel system in their boat — that’s also an option for doing it yourself, albeit a more expensive one).
Tools Needed to Do It Yourself
It costs about $100 to get the tools needed to do it our way, assuming you already have a drill (or use an electric pump) and have or borrow jerry cans.
To polish your fuel yourself, you need:
- A way to pump fuel out of your tank(s). If your boat uses diesel, you can use a simple drill pump as diesel is not explosive — that’s what we do. You can also use various electric fuel pumps designed for diesel. DO NOT use a drill pump with gasoline — instead use a pump that’s approved for use with gas.
- Jabsco Drill Pump on Amazon (same one as we have although we bought ours in an “emergency” situation at West Marine for quite a bit more) — we use ours with a Ryobi Cordless Drill and the lithium battery packs (we have two 18-gallon tanks and can pump one completely out with one fully-charged battery and there’s still juice left in the battery)
- 12 volt Diesel Transfer Pump with Alligator Clips on Amazon — we do not have this but friends do and are happy with it. The big thing is having power available (you can replace the alligator clips with a cigarette lighter style plug if you have a handy outlet, too).
- A weight on the end of the pickup tube so that you can get all the contents of the fuel tank. Dave had some weird fitting — basically a bolt with a hole through it — but a couple of stainless nuts work too (use something that won’t rust). Make a hole through the tubing and use a piece of seizing wire to keep the weight from slipping off.
- Sufficient containers to hold the contents of one tank. Jerry cans are great and you may be able to borrow some empty ones from friends, too. You can also use 5 gallon buckets lined with clean trash bags. Whatever you use, you have to have sufficient containers to be able to remove all of the fuel from one tank at a time. You can, of course, transfer the fuel from one tank through the filter and into another if you have an empty tank (you may want to clean the empty tank first).
- A water and particulate filter. Cruisers have used Baja filters for years, but they are no longer made and used ones sell for a minor fortune. We have a Baja filter, but I’ve talked to a number of people who have other brands and the “Mr. Funnel” ones sold on Amazon are considered to work better than anything else. I have no personal experience but several people have told me that the West Marine filters do not nearly as good a job of filtering water out (you can test your filter by pouring water into it and seeing if any comes out the bottom — none should).
- A way to transfer the fuel from the jerry can through the filter and into the tank. Yeah, you could hand pour it (if so, you’ll have a sore back!). You could use the same pump that you used to get the fuel out of the tank. But the far easier and faster way is to use one of these nifty shaker siphons (read more about them here if you’re not familiar with them and how to use one).
- Container to put any water caught in the filter into, for transport to an appropriate disposal site.
- Rags, paper towels or blue shop towels. To catch spills as necessary.
How to Do It
- Pump all the fuel from one tank into jerry cans or other containers. You can use the water/sediment filter as you’re filling the containers or you can filter it as it goes back into the tank. (You can filter it on both transfers if you fear serious contamination.)
- Wiggle the pickup tube around as much as you can to make sure you’ve gotten as much fuel out as possible. If the boat is in the water, have anyone else on board move so that one part of the tank is lowest and you’ll get the most.
- If you filter the fuel coming out and find a lot of water or sediment, it’s a good idea to go ahead and clean the tank before you refill it. How you do this depends on your tank configuration . . . maybe by wiping out the inside through an inspection port (how we did it on our Tayana 37). On our current boat, the only way to do it is to remove the tank then remove the pickup tube from the tank, then go through that hole with a rag on a stick.
- If you filtered the fuel coming out of the tank, you can simply use the shaker siphon and put the fuel directly into the tank now. Otherwise, put the funnel filter into the fill hole and use the shaker siphon to put the fuel into the funnel filter and filter the fuel as it goes into the tank. Dave finds it easier to filter at this point, but it means that if he finds lots of water or gunk and decides he needs to clean the tank, he has to pump the fuel back out of the tank again to do so.
- Whenever you are filtering the fuel, if the filter really slows down, check it for both sediment and water. Clean the filter if necessary. Pour any water into the container for this purpose and dispose of it properly.
- Repeat for any other fuel tanks.