re: copper crush washer vs aluminum

[Phil Rose <pjrose@servtech.com>]

>From: Craig D. Niederst <niederst@telerama.com>
>To: quattro@coimbra.ans.net <quattro@coimbra.ans.net>
>Date: Friday, April 24, 1998 6:04 PM
>Subject: copper crush washer vs aluminum
>
>
>>I finally got that damn drain plug out and went to the dealer (Day Audi)
>>over lunch today and bought a new drain plug. I was issued an aluminum
>crush
>>washer with the plug instead of copper. I questioned the parts manager, and
>>he told me that this is what Audi has been sending them. He said he hasn't
>>seen a copper washer in a couple of years. He said they only use these
>>aluminum ones on the Audi's they service. I remember a while back that a
>>lister mentioned aluminum washers were detrimental due to the metal types
>>not being compatible (i.e. oil pan metal and aluminum). I have already
>>installed the new washer, and changed the oil. Was this a mistake to use
>the aluminum washer? TIA.

>>Craig
>>'92 100S (71k)
>
>
>Hi Craig;
>
>    They are still selling the copper washers here. I've never seen an
>aluminium one.
>    The problem you are referring to is galvanic corrosion between the steel
>oil pan and plug and the aluminium washer. The aluminium will corrode
>preferentially; the washer will dissappear at a rapid rate given the proper
>conditions (hot - yes, electrolyte - not too likely unless you drive your
>car on ocean beaches or Canadian winter roads). If you change the oil at the
>recommended intervals (or sooner!) I doubt that you will have a problem in
>any case.
>
>HTH
>
>Fred Munro
>'91 200q  250k km

Could there be a problem (unrelated to corrosion) if an aluminum washer
were   used on an _aluminum_ oil pan (as on '91 200q--and others?)? I
recall (years ago) being cautioned to avoid use of washers made of the
identical metal as the substrate--since high tightening torques can cause
metal-to-metal bonding to form between soft metals (galling?). That could
cause significantly greater forces needed to separate the components (and
perhaps damage the mating surfaces). Of course with drain plugs, if
reasonable torques are used and the surfaces are oily, this actually may
never be an issue.

Anyway, last week I dropped by John Holz Audi in Rochester and asked for a
copper washer for my '91 200q 20V oil drain. I immediately rejected the
puny 3/4" thing the parts guy brought out, which he was _certain_ was
correct. "No," I insisted, "it's a _lot_ bigger than that." A few moments
later he returned and said, sheepishly, "You're right, here's the one for
your car." About 1 1/8 " OD. And a whopping 73 cents.

Phil Rose		Rochester, NY
'89 100
'91 200q		pjrose@servtech.com