Biodiesel warning- tank gaskets of either Viton or Teflon, or NOT

by Glen Tuttle, Cruisers' Network Online on 13 Apr 2010 It's when one experiences first hand the bad effects of using biodiesel without changing the fittings on the fuel tanks that the message comes home in a dramatic way: This is one cruiser's story, Glen Tuttle, of the Cruisers Network Online, cruising in the Caribbean:

Biodiesel is showing up throughout the Caribbean now. We just filled up in Cartagena at the Texaco fuel dock at Club de Pesca where a sign advertised they are now using Biodiesel. Biodiesel is renewable fuel produced from vegetable or animal fats and oils. Biodiesel is significantly less toxic to the marine environment than petroleum derived fuel. Biodiesel will not harm fish or people. Those working around running diesels using biodiesel find the exhaust fumes to be less irritating. That's the good news. Here's the bad news, and our story:

We have large inspection ports on our two 300 gallon diesel tanks. About 2 years ago Cristobal Marine Repair in Panama did some work on our tanks and replaced the inspection port gaskets with Buna-N gasket material, which is pretty well recognized as the standard for diesel tank gasket material. When we filled up the tanks in Cartagena we noticed a slight weeping on one of the ports, but it stopped once I tightened the nuts holding the inspection plate on.

But I questioned why the nuts needed tightening. Perhaps the gasket had compressed?

Then while underway from Cartagena to Colon, Panama, the racor filter vacuum gauge on one tank as well as the gauge on our fuel polishing system started showing a high vacuum. Not good news, especially at 0400 in 8' seas. Next, the port engine (caterpillar 3208) drawing fuel from the suspect tank began to falter. Really not good!. I immediately put that engine in neutral and changed the valves so that both engines would receive fuel from the other
tank. We made it to Panama without further incident.

When we removed the inspection port on the suspect tank, both Buna-N gaskets were totally disintegrated, and chunks of it had stopped up the fuel ports. We checked on the other tank and same thing happened, but to a lesser degree as those gaskets were only about a year old.

An hour of Internet research revealed:

All known gaskets, seals, hoses and O-rings are compatible with blends of l ess than 20% biodiesel. For higher BioheatR fuel Blends than 20% biodiesel, up to and including 100% biodiesel, compatibility will depend on the materials they are made from. For BioheatR fuel Blend concentrations over 20% biodiesel, fluorinated polyethylene, fluorinated polypropylene, Teflon, Teflon lined, or Viton Components are recommended. Use of other types of materials in BioheatR fuel Blends over 20% biodiesel such as nitrile, natural rubber, or Buna-N type rubbers may cause leaks, plugged filters (due to dissolved material) and eventually complete gasket, seal, hose or O-ring failure.

We were incredibly lucky we didn't have both engines and generator shut down in the middle of the night in rough seas. I have contacted Cristobal Marine Repair and plan to have a lengthy conversation with them about the material
they used. It appears that any vessel having the possibility of taking on Biodiesel fuel should have tank gaskets made of either Viton or Teflon, certainly not Buna-N. The problem doesn't stop with gaskets. The Biodiesel will attack fuel hoses, o-rings, and seals. But it supposedly won't harm fish!