How to Buy an Oil Sump Drain Plug or Washer

My daughters car had an oil leak. Luckily for me, the leak was coming from the oil filter housing. An easy fix, buy a new filter (the housing oil seal is often supplied with a new filter). While I was at it, the car needed an oil change, so I went ahead and drained the oil…

The original leak in the oil filter housing was now fixed, but on changing the oil, the sump drain plug now started to leak. I couldn’t get it to stop..!

Oil Drain Sump Plug & Copper Washer
Oil Drain Sump Plug & Copper Washer

What Did I do to Fix the Drain Plug Leak?

Well, the shops were shut, so I dug around in my box of washers (for a sealing washer). They were all too big or too small! I was scratching my head what to do? I needed to get it fixed. I had some old copper pipe. So I used this to make a new washer. I fitted the homemade copper washer to the sump plug. It partly worked, but there was a very slow leak. It would do for now, but I needed a proper replacement when the shops opened…

Topics:


Types of Drain Plug?

Drain plugs are generally a bit like a bolt that screws into a hole to stop fluids escaping. However, most bolts won’t work, as the thread will let fluids pass. A drain plug often has a different type of thread (often called ‘pipe threads’ or ‘taper threads’) to prevent fluids leaking past. Washers can be an addition to enhance the seal, where repeated use can reduce their efficiency. Where ‘pipe’ or ‘taper’ threads aren’t used, the seal relies wholly on the sealing washer.

Drain plugs can also have:

  • Different heads (or methods of unding), using different types of socket:
    • Hexagonal head.
    • Torx.
    • Spline.
    • Allen key.
    • A specific drain plug key.
    • etc.
  • They may also be magnetised on one end to trap metal burrs and filings from engine wear.

How to Fix a Leaking Oil Sump Drain Plug?

There are a few options you can take, dependant on the cause of the leak. Should I replace with:

A New Oil Sump Drain Plug:

A straightforward like for like replacement for your old oil sump drain plug. These should be available from your car parts supplier. Try and ascertain if the leak is due to the washer, or the drain plug. Unfortunately, this check tends to be purely visual, and may be difficult to see?

Note:
  • Most oil sump drain plugs have sealing washers. If yours was one that didn’t have one fitted, you may want to consider fitting one?
  • Make sure you have the correct size drain plug and check the type of socket that’s needed for it, (in case it’s different to the original and you don’t have one that will fit?).

A New Oil Sump Drain Plug Replacement Washer:

There are several different types of sealing washer…

Copper:

A copper washer is the most common type of sealing washer for oil sump drain plugs. They say to never reuse sealing washers, but the copper sealing washer will probably survive reuse better than most.

Note:
  • Copper hardens with use. Therefore it may not provide such a good seal second time round...
  • You can anneal (soften) copper, by heating till it’s pinkish red and leaving to cool naturally, (or quenching in water).

Copper (Crush Type):

Copper Washer (Crush Type - Used)
Copper Washer (Crush Type – Used)

A copper crush type sealing washer provides a good seal but must not be overtightened. They should only be used once, as the one time crushing action provides the seal.

O’Ring:

O'Ring (Used)
O’Ring (Used)

An o’ring is often used to seal an oil drain plug (and is often seated in a slight recess). These can be damaged easily, so should be checked, or replaced often when checking / changing the oil.

Dowty Type (Metal & Rubber):

A ‘Dowty’ type of sealing washer is often used for high pressure applications, for sealing gases, oils, and other fluids. They are made out of various metals incorporating a rubber type seal.

Dowty type sealing washers will wear quickly if reused and retightened.

Nylon (plastic):

A nylon type of sealing washer has low friction and can withstand various chemicals. Nylon (particularly Nylon 6/6) can withstand high temperatures. Nylon also has ‘adsorption properties’, which allow it to compress providing a seal.

They should probably not be reused if they become overly compressed or deformed.

Fiber:

A fiber washer is great for many applications, such as oil sump drain plugs. They can compress to provide a seal, plus they have the added ability to absorb fluids. Absorbing fluids has the benefit of allowing the washer to swell slightly, thus providing a better seal. They must not be overtightened.

Fiber washers will wear quickly if overtightened, or re-used.

Aluminium:

An aluminium sealing washer is similar to copper, but is softer. It is therefore able to compress and seal slightly easier, but will wear more quickly than copper.

Conclusion:

A copper sealing washer is probably the pick of the bunch for oil sump drain plugs (for wear and tear). However, the other types will probably form a better seal, but wear more quickly. Having to be replaced after every use.


When it’s Not the Washer…

There are a few options you can take.

  • If the oil sump drain thread is worn or stripped, you can buy a new oversized sump drain plug that cuts a new thread when inserted and replaces your old drain plug.
  • You can use a Helicoil.
  • A sump drain plug repair kit.
  • A new sump.

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