Nitrile or Viton 'O' ring for diesel filler cap seal?

[PetiteFleur]

Title says it all, I topped up my diesel tank yesterday and noticed water on the screw thread. Originally 42 ID x 2mm diameter cross section so will increase to 3mm cross section. No maker's name on the filler cap. Nitrile or Viton?

 

[Minchsailor]

Having worked in the chemical industry, I suspect there is not much difference between them. In practice a very small area of the O ring is exposed to Diesel. I recently had to replace mine as they showed signs of degradation (after >10years) and I used whatever the local industrial suppler shop had was available.

 

[Plum]

Title says it all, I topped up my diesel tank yesterday and noticed water on the screw thread. Originally 42 ID x 2mm diameter cross section so will increase to 3mm cross section. No maker's name on the filler cap. Nitrile or Viton?

I have always used Nitrile and never had a problem. Current one is more than 8 years old. I keep it and the threads greased with Vaseline.

Www.solocoastalsailing.co.uk

 

[Poignard]

I have just renewed mine (43 x 3mm).
According to ASAP's catalogue the original O-ring was neoprene but I couldn't find any in that size and material.
Simply Bearings Ltd suggested nitrile and I have gone with that.
They are sold in twos, so I have a spare.

 

[Ammonite]

Either will be fine with diesel. Viton is more tolerant of a wider range of chemicals and temperature but its not relevant in this case

 

[superheat6k]

Whatever you use I suggest thoroughly smothering the O seal and cap thread with a decent amount of thick waterproof grease. OK so your fingers get a bit gooey when refilling, but you completely eliminate the number 1 cause of water entering your fuel tanks.

 

[PetiteFleur]

Thanks everyone, I had looked a Simply Bearings and will probably go them for Nitrile. I measured the original but may go with Poignards suggestion of 43 x 3.