Gen 2 H6 fuel pump O-ring failure- Ethanol?

[CNY_Dave]

Just hit me, forgive me if this was mentioned in the individual threads- could the O-ring failure (swelling) be because this o-ring in this pump (or maybe just some lots) is susceptible to swelling from ethanol?

The swelling might even be the cause of the tab cracking.

Dave

[1 Lucky Texan]

At first, I thought, 'hey, we just need to correlate where folks with the problem live and use of ethanol.' But, I think something like 90% of metro areas use it right?

interesting detail for sure but....i dunno.

I suppose, if there were zero reports from areas known to never have ethanol, that could be a damning piece of evidence. problem is, I'd bet for every report we've seen, there are several that were just repaired at a dealer and the car's owner was just told - "you had a bad fuel pump"

[Seabass]

I doubt it. Fuel systems have been ethanol safe since the 80's.

[grossgary]

Originally Posted by CNY_Dave

Just hit me, forgive me if this was mentioned in the individual threads- could the O-ring failure (swelling) be because this o-ring in this pump (or maybe just some lots) is susceptible to swelling from ethanol?

The swelling might even be the cause of the tab cracking.

Dave

i was wondering the same thing. I think I can answer this and give us a test that would prove one way or the other.

Mine failed, one partially cracked tab and the oring squished out. I fitted a new oring with the cap that had broken tabs. It lasted a bit over 200 miles and failed again. i had an extra oring and hose clamps to hold the cap on just in case so i got it back on the road easily until I located a good used cap. here's the key:

***when i removed the "new" oring (one day old and 200 miles) it looked exactly like the old one that had failed - waaaay stretched out. it was not even close to reusable.

so this tells us that whatever is causing it can happen very quickly.
but i don't think it's ethanol.

given that it happened so fast on mine that gives us a very easy test. simply place an oring in ethanol gasoline and see how it does after one day. you can even stretch it over a can or something to give it some tension (easier than trying to find compression).

but i think that's highly unlikely to be the case so i'm not doing the test.

i just got a cap from a board member and he happened to include the original old oring and it looks perfectly sized - though aged, not stretched at all. i highly doubt it avoided ethanol gasoline the past 10 years and who knows how many miles before hitting the junk heap.

based on my experience i think the tabs crack and then the ensuing pressure relief from the cap sealing surface and fuel pressure is enough to slowly push the oring out from under the cap...a little bit, then some more, etc. until it's hanging out and the car won't run.

the key is the orings are *really* stretched out....

i'd be curious to know why the caps are cracking....

[CNY_Dave]

Yeah, and why aren't the H4 caps cracking?

Are the pressure specs a lot higher on the H6?

[grossgary]

Originally Posted by CNY_Dave

Yeah, and why aren't the H4 caps cracking?

Are the pressure specs a lot higher on the H6?

oh wow - this isn't happening on the H4's? i didn't know that.

the H6 and H4 fuel pumps are "different" - though i'm not sure what that means.

[1 Lucky Texan]

is it always the tab with the ground wire? maybe it's just shock/vibration on that tab from the xtra mass of the wire?

Wonder if failure is more likely on cars driven off-pavement? Or cars driven around mostly empty?( less buoyancy/dampening from the fuel.)


also, check this out; http://www.ultimatesubaru.org/forum/...64#post1117764

[Euchre]

Ethanol isn't suddenly there in our gas when it wasn't at all before. Ethanol has been added to gas for decades, just in smaller amounts. The permitted ratio of ethanol to gasoline has risen over time, and thus fuel systems have been made to cope with it for quite a while. If your car was made in the 70s or earlier and still has all the original fuel system parts, it might be an issue - but most of those used mechanical fuel pumps and not so many rubber or synthetic O-rings.

The engines that are being hurt by recent jumps in ethanol content are the ones not on the street - boats and small engines. Small engines from as recently as 6 years ago just weren't made with 10-20% ethanol fuel in mind. If you look around, you'll notice many marina gas stations say 'ethanol free'.

[andykane]

It's definitely also a problem with the 4 cylinders. My 2000 2.5L had a tab crack and the resulting problems. I ended up getting a junkyard fuel pump assembly but had some problems that seem to have been caused by that O-ring not sealing properly. I replaced it with a viton o-ring in the correct metric size and it's worked perfectly every since.

A lot of the o-rings sold at parts stores seem to just be butyl rubber which, I believe, breaks down quickly in gasoline/ethanol. It's also not easy to find the correct size.

The crack on mine looked like a fatigue thing. Possibly due to the wire, or possibly due to cyclic loading on the cap. With a new o-ring the fit is very tight and the fuel pressure should remain fairly high and constant even when the car off. With a looser fit the pressure can leak down while parked and I could possibly see the cyclical pressurization-depressurization eventually causing a problem, especially if there was a rough edge on the cap for the crack to start from.

For posterity, although it's mentioned in another thread on the subject, I used a -928 metric o-ring with a 3mm thickness x 53.09mm ID (not sure if the -928 is standardized - the shop I got it from just used the dimensions).

[CNY_Dave]

I do see this mentioned a lot more for H6s than H4s- previous post is first H4 mention I recall.