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Discussion Starter · #1 ·
I am confused as to why the oil drain plug uses a copper washer. If a good seal is required between the sump and plug, wouldn't a silicone washer be more appropriate?

Is there some metallurgical reason for using copper?
 

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I believe it has to do with attaining the proper torque, and being able to seal properly without the chance of unscrewing. The copper will crush to conform and seal... I’ve heard of people Annealing (heating up to puff up the squashed washer) with a gas torch to reuse that copper washer . But I just buy a new one for the plug .
 

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Discussion Starter · #3 ·
I believe it has to do with attaining the proper torque, and being able to seal properly without the chance of unscrewing.
I appreciate your response. However, it doesn't explain the need for copper.

If it is a matter of sealing, then there are lots of materials with superior sealing properties.

If it is just a matter of proper torque, no washer should be necessary. The gearbox drain and fill plugs have no sealing washers and are torqued to a much lower setting without risk of unscrewing.
 

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I think the gearbox had quite a few more threads to engage therefore a washer is not needed.
Not sure how a silicone washer would take being cycled between 200F and like 0F in some regions. You also wouldn't be able to torque it down and it would come loser with vibration. And I would imagine with a silicone washer there's a chance while tightening, the washer would just stretch and not actually seal anything. Basically would slip over the head of the bolt.
 

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Discussion Starter · #5 ·
That actually sheds some light. A material is needed that is hard enough to take the torque and soft enough for a good seal.

In that case, I wonder why an aluminum gasket wasn't used. Copper and aluminum tend to react with one another. With the sump being made of aluminum, a copper gasket would seem to be a poor design choice.
 

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High performance snowmobiles have used copper head gaskets for years with few problems. Never had any leaks on my oil pan plugs.
 

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FWIW, many of us continue to use the original washer at each oil change, with no leaks. YMMV, of course... :)
 

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Discussion Starter · #10 ·
Sump drain plugs are the only place I have ever seen these copper washers used. I was just curious why that is.

Of course, this is all academic. The manual says to use a copper washer, so a copper washer I will use :)
 

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Sump drain plugs are the only place I have ever seen these copper washers used. I was just curious why that is.

Of course, this is all academic. The manual says to use a copper washer, so a copper washer I will use :)
You'll find copper washers for the connections between brake lines and and calipers/wheel cylinders as well.
 

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I own a bunch of cars of different makes that use different engine oil drain plug seals. For example:

VW (2000s and newer) steel washer
Saab: (1980s) Dowty Washer (steel washer with rubber bonded inside)
Fiat: orange silicone washer

There are a bunch of ways of doing this. I suspect that using a new or annealed copper washer would keep threads from stripping on these oil pans because they'd require less torque to seal.
 

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I know this does not answer your question, but I over torqued my 2008 Smart car engine oil drain plug and stripped the threads out of the pan aluminum housing. For years, I have been using make a gasket silicon and it works great, no leaks. Apparently, there is hardly any pressure. Off course, I let the silicon cure before adding the new oil.
 

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What’s a few drops of oil? Now and then? Keeps the alloy from oxidizing and looking like hell. lol I don’t think I’ve ever actually replaced a copper washer myself. Clean and reuse.
 

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I appreciate your response. However, it doesn't explain the need for copper.

If it is a matter of sealing, then there are lots of materials with superior sealing properties.

If it is just a matter of proper torque, no washer should be necessary. The gearbox drain and fill plugs have no sealing washers and are torqued to a much lower setting without risk of unscrewing.
Part of the reason may be that copper has been used because of its malleability since the 1930s for certain items, and the fact that it resists corrosion of the type that would affect other materials available at the time.
Back in the 1930s, when copper washers started to be used, there were not the huge variety of materials available at reasonable prices. At that time, people used washers made of sintered metal and cardboard or fiberglass, among other mixes. It's more tradition and the fact that engineers often don't change items in a mass-produced product if it works as is and is considered cost-effective.

This gives inquiring amateurs the opportunity to excel and even start companies based on their discoveries and efforts.
 
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