Regularly replacing O-rings is an important part of boat maintenance. When we prepared to sail to the Bahamas in 2016, we missed something small that turned into a big problem.
What Happens When You Don’t Replace O-Rings
We never thought to check the O-rings on the deck fills for the fuel tanks. This one was deteriorating and cracking, and letting both rain and deck wash water into our starboard fuel tank. Actually, we did cursory checks. Every time Dave filled the diesel tanks, he looked at the O-ring. But he never actually removed it to examine it closely.
This one looked just fine in place and even when first removed. It wasn’t until I bent it and took this photo (above) that I zoomed in closely enough to see the cracks. (We filter all the fuel as it goes into the tanks so we know we did not purchase bad fuel.)
We ended up with a “chocolate milk” mess of water emulsified in the diesel fuel. This is a sample we removed from the tank:
Good diesel fuel, by contrast, is totally clear – usually either yellow or pink in color in the US:
I won’t rehash everything that happened, but getting that water in the tank caused us to turn around just 10 miles into a planned 80-mile trip across the Bahamas Banks. The wind turned out much lighter than forecast, which made sailing as we drained and changed fuel filters painfully slow.
We returned to an anchorage that we knew we could enter and anchor in under sail, although we did manage to keep the engine running just long enough. It was sputtering again as we dropped the anchor.
Important Tips for O-Ring Maintenance
Hopefully, you’re now convinced to add replacing your O-rings to your annual maintenance schedule. But there are a few other tips that are important to know.
Check O-Rings After Boat Storage
Several boat owners have told me they discovered water in their fuel after several months with the boat on the hard. Some parts (like impellers, for example) wear out more quickly after disuse. Could that be true for O-rings as well?
I can’t say it for certain, but it might be a good idea to add replacing your O-rings to your list of boat chores when you return to the boat after a long absence.
Inset Filler Caps May Be More Vulnerable
I haven’t done a scientific study, but I suspect that our inset filler cap may be more vulnerable to water intrusion than those whose edges overlap the opening. If your boat has the same kind, you want to be particularly rigorous in replacing your O-rings regularly.
If You Can’t Replace an O-Ring Immediately
We couldn’t find the O-ring we needed in the Bahamas. So we applied silicone grease and covered the ring with butyl tape.
We kept Sil-Glyde (Amazon) on hand for our watermaker O-rings, so it was handy. You can also buy it at most auto parts stores. Read more about maintaining gaskets and weatherstripping with Sil-Glyde.
Different O-Rings for Different Uses
Not all O-rings are alike. They’re made of different materials for different uses. For example, O-rings made from rubber or latex deteriorate when they come in contact with petroleum products. Rings for fuel fills are made from something like Viton, a material that resists petroleum infiltration. O-rings for water fills are much cheaper and made from rubber.
Make sure you’re buying the type you need, or you might experience the same problem.
Where to Buy O-Rings
Our boat had a Perko filler assembly. I googled replacement O-rings for Perko fills. You can do the same for any filler assembly.
You can also take your old O-ring to an auto or marine parts store. Make sure you tell them where you’ll be using it so they give you one made for that purpose (see above).
I did a quick search on Amazon for diesel fuel fill O-rings. I primarily found products for gasoline engines, despite specifying diesel. Here is a link to Viton O-rings in various sizes on Amazon.
The Cost of Not Replacing the O-Ring
The cost of not replacing that O-ring in time?
- One very long day on the water. It took us 7 hours to cover those return 10 miles. Numerous Racor drainings and changes hanging on the back deck over the engine compartment while underway.
- Five Racor filters (replacements cost $36 each in the Bahamas, but that’s a lot less than getting bad fuel in the engine and having to rebuild it or repower)
- 16 gallons of badly contaminated diesel fuel (the entire contents of that tank) (our DIY fuel polishing supplies allowed us to get all the contaminated fuel out)
- Four days in a marina to be able to get rid of the bad fuel, get fresh fuel, resupply the Racors, and have hot unlimited-water showers at the end of the day when we’re covered in diesel
- Lost window for crossing the Bahamas Banks to the Berrys
Oh, and a day lugging 5-gallon jerry cans first of bad diesel, then of good to and from the boat, over the lifelines, and so on. Talk about exhausted!
Another cruiser, Cherie, shared a similar story with even more damage. The water corroded the fuel injectors, which they also had to replace at significant additional expense. Whew! What a ton of heartache that’s easy to avoid.
Those o-rings? We got 2 for about $10. We made them part of our annual maintenance ritual, along with changing the ones on our water fills.
Hopefully, now that you know, this won’t happen to you.
More On Fuel Systems & Problems
Carolyn Shearlock has lived aboard full-time for 17 years, splitting her time between a Tayana 37 monohull and a Gemini 105 catamaran. She’s cruised over 14,000 miles, from Pacific Mexico and Central America to Florida and the Bahamas, gaining firsthand experience with the joys and challenges of life on the water.
Through The Boat Galley, Carolyn has helped thousands of people explore, prepare for, and enjoy life afloat. She shares her expertise as an instructor at Cruisers University, in leading boating publications, and through her bestselling book, The Boat Galley Cookbook. She is passionate about helping others embark on their liveaboard journey—making life on the water simpler, safer, and more enjoyable.
Franz Alvarez says
Hi there! It’s not just the fuel cap; change the O-rings on the domestic water tanks to prevent dirt and salt water from seeping in. Change the holding tank cap’s O-ring too – no need to make that science experiment worse. We’re not full-time cruising yet, but every spring they all get changed and I keep two sets of spares in a ziplock bag. Like you said, cheap insurance.