Hot start problem resolved due to failed check valve in the DMCH fuel pump

[rdarlington]

What were the original o-rings made out of? Mine is original and I pump the cheapest gas I can find. Buna rubber o-rings are considered to have excellent compatibility with ethanol for both static and dynamic applications. Basically, the same compatibility as viton.

-Bob

[kings1527]

My terminology is mixed up. You're right. Viton (not nitrile) is the stuff that's been widely regarded in the forum to have the best compatibility with ethanol. Buna-N supposedly still has problems. As to what the originals were made of, I'm not sure but I'm guessing they held up better back in the day due to the fact that ethanol hadn't been introduced yet.

[NightFlyer]

Buna-N is NOT ethanol resistant - it will deteriorate when exposed to ethanol of any concentration - higher concentrations will cause faster wear.

Viton has been independently tested to be impervious to ethanol concentrations as high as 15%, although DuPont claims it can handle much higher concentrations without issue.

[rdarlington]

Buna-N is absolutely compatible with ethanol, in concentrations as high as they get (don't get me started on azeotropes).

Every o-ring manufacturer out there lists this and Buna-N (nitrile) is the recommended material for sealing with o-rings for ethanol.

[rdarlington]

Actually from what I'm reading, Viton is actually a poor choice for ethanol. It's marginal at best.

Simply put, if Buna-N o-rings are deteriorating because of modern fuels, it is most definitely NOT because of the ethanol in them.

-Bob

[Bitsyncmaster]

It's a good question about original O-rings. My guess is they are Buna-N but maybe were a smaller size. I tested Buna and Viton side by side soaking in ethanol gas. The Buna expanded quite a bit and the Viton did not change at all. So if my guess is correct, the smaller size keeps Buna-N working.

[kings1527]

Actually from what I'm reading, Viton is actually a poor choice for ethanol. It's marginal at best.

Simply put, if Buna-N o-rings are deteriorating because of modern fuels, it is most definitely NOT because of the ethanol in them.

-Bob

Not sure where you're reading about Viton being a poor choice for ethanol but that's not right. It's not so much a matter of deterioration, but rather swelling resulting in deformity. That's why the PPR o-ring starts having problems. It becomes malformed and can't hold rest pressure. I've personally (as have others) seen a nice swollen buna-n o-ring from ethanol based fuel.

In short, go with Viton unless you want to look cool working on your car all the time.

And a special thanks to Dave M for all of his research and info on this.

[rdarlington]

Not sure where you're reading about Viton being a poor choice for ethanol but that's not right. It's not so much a matter of deterioration, but rather swelling resulting in deformity. That's why the PPR o-ring starts having problems. It becomes malformed and can't hold rest pressure. I've personally (as have others) seen a nice swollen buna-n o-ring from ethanol based fuel.

In short, go with Viton unless you want to look cool working on your car all the time.

http://www.sterlitech.com/oring-compatibility-chart


I see viton listed all over the map for both gasoline and ethanol.

One thing I see that's consistent is Buna-N for both gasoline and ethanol resistance. It is *the* recommended material for both. Who is manufacturing your o-rings? Are you sure you're getting what you're paying for?

Just an FYI, I have extensive experience in the vacuum technology and industrial chemistry world and deal with chemical compatibility for these types of seals for both terrestrial and space applications. What I think is that you guys are picking up 3rd rate o-rings and are making assumptions. The available data out there from the manufacturers and industry publications suggest that Buna-N is the stuff you want for o-rings for cars. They've been using ethanol in gasoline since the 1920s (granted, the o-ring didn't exist in the 1920s) and is not new.

There are plenty of reasons to go with viton, but I don't think I know of any where it comes to dealing with cars.

-Bob

[NightFlyer]

Deteriorate wasn't the best word to use - should have been 'compromised' instead.

Whether it's being caused by the ethanol or something else, fact remains that Buna-N is compromised by today's standard fuel blends, whereas Viton is not. Dave M's side by side is consistent with the results of other comparison tests that I've seen. Alex's recent personal experience would also seem to validate/support the concerns about using Buna-N in applications on our cars.

While the choice is yours to make, I can personally attest to the fact that I haven't encountered any issues running Viton rubber in the fuel system components on my car.

The difference in price between the two materials is marginal/nominal at best...

[Bitsyncmaster]

It only takes about a one or two hour soak in gasohol if you have some calipers to do the test I did.

Measure each before you soak, Tag which is which, soak and remeasure. I would like another verify of what you find.