Ok, I have changed oil several times using topsider. Recently looking at new oil filter package and besides the 2 o rings or gaskets that go on the filter cover housing I have a small copper washer.

Is this washer for the bolt that goes through the filter housing cover or for the drain plug if you drained the oil from the oil pan?

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95 E420 ( 76K) SOLD
85 380SE(125k)
95 SL500(72k)

Yes. It seals the bolt to the filter canister.

If the washer came with the filter it goes on the filter canister bolt. If you remove the pan drain bolt you can reuse the old washer if you anneal it. Hang the washer on a piece of wire, heat it with a propane torch until it glows red and then quench it immediately. This softens the copper to the original hardness and you can reuse. Barring the high tech, most parts stores have an assortment of copper washers.

I use mine for the drain plug. I don't know what "bolt through the filter housing" you are referring to. Please explain if you can. I assume our cars have a similar oil filter setup. I don't want to misuse the washer and miss something important!

Thanks a bunch.

It goes to the plug on the oil pan.