Why the Humble Oil Drain Plug Washer Is Critical for a Leak-Free Engine

While many vehicle owners focus on the oil filter or type of motor oil during maintenance, one small yet essential component often gets overlooked—the oil drain plug washer. Whether you're dealing with an M14 crush washer, a reusable oil plug washer, or a general-purpose oil drain washer, this tiny part plays a major role in preventing oil leaks and protecting your engine. In this article, we’ll break down the different types of washers, their functions, and how to choose and replace them correctly.

The Role of the Oil Drain Plug Washer

Every time you change your engine oil, the drain plug must be removed and reinstalled. When reinstalled without a proper seal, oil can slowly leak from the drain hole—posing a risk to both your engine and the environment. That’s where the oil drain plug washer comes in.

This washer sits between the oil pan and the drain plug to:

Create a tight, leak-proof seal

Distribute pressure evenly as the plug is torqued down

Prevent damage to the oil pan surface

There are two main types of oil drain plug washers: crushable (single-use) and reusable. Each has its own benefits and use cases.

What Is an M14 Crush Washer, and When Should You Replace It?

A crush washer is a type of single-use washer made from soft metals like aluminum or copper. These washers deform slightly when the drain plug is tightened, creating a precise seal that conforms to the surfaces involved. One of the most common sizes used in modern vehicles is the M14 crush washer—designed to fit M14-threaded oil drain plugs.

Benefits of using an M14 crush washer:

Excellent sealing due to precise compression

Ideal for aluminum oil pans or other soft-metal surfaces

Cost-effective and widely available

However, because they deform when crushed, these washers should never be reused. Reinstalling an old M14 crush washer can result in a poor seal, leading to oil drips or worse, a sudden loss of engine oil.

Most manufacturers recommend replacing the oil drain washer with every oil change, especially if your vehicle uses a crush-type washer. It’s a small investment (often less than $1) that can save you from major repair bills caused by leaks.

Understanding the Difference Between an Oil Plug Washer and an Oil Drain Washer

Although terms like oil plug washer and oil drain washer are often used interchangeably, they technically refer to the same component: the washer that seals the oil drain plug to the oil pan. However, there are subtle distinctions worth noting.

The oil plug washer refers specifically to the washer attached to the plug itself, whether it's crushable or reusable.

The oil drain washer often refers to the washer’s role in sealing the oil drain opening of the engine's oil pan.

Common types of oil plug washers include:

Aluminum and copper crush washers

Nylon or fiber washers (used in some European or older vehicles)

Rubber-bonded metal washers (reusable and often OEM-standard)

Choosing the correct washer material is crucial. For example, rubber-bonded metal washers provide reusable convenience and excellent sealing but may not be compatible with all vehicle designs. In contrast, copper crush washers provide excellent conductivity and deformation properties, ideal for high-performance or older engines.

If you're unsure which type of oil plug washer your car uses, consult the owner’s manual or an OEM parts diagram. Using the wrong type can either result in a leak or make the plug difficult to remove at the next oil change.

Tips for Choosing and Replacing an Oil Drain Washer

Properly replacing the oil drain washer is one of the easiest but most commonly skipped steps during an oil change. Here’s how to do it right:

1. Determine the Correct Size

Most modern vehicles use metric sizes like M14 crush washer, but others may require M12, M16, or even SAE sizes. Always match the washer to your specific plug thread and diameter.

2. Select the Right Material

Use copper or aluminum for one-time use crush washers. If you're looking for durability and easy maintenance, consider switching to a rubber-bonded washer.

3. Inspect the Oil Pan and Plug

Before installing a new washer, ensure that the oil pan’s sealing surface is clean and free of nicks or corrosion. Also inspect the plug for wear or stripped threads.

4. Torque to Spec

Don’t overtighten the oil plug. Over-torquing can distort the washer beyond its sealing limit or damage the threads in the oil pan. Use a torque wrench to apply the manufacturer’s recommended torque (typically 25–35 Nm for most cars).

5. Always Replace Used Crush Washers

Even if the washer “looks fine,” reusing a crushed washer can result in oil leaks. Keep a few spares on hand to make oil changes cleaner and more reliable.

Final Thoughts

Though small in size and often under a dollar in cost, the oil drain plug washer plays a vital role in keeping your engine oil where it belongs—inside the engine. Whether you're using an M14 crush washer for a clean, single-use seal, or relying on a reusable oil plug washer, don’t skip this step during your oil change.

By choosing the correct oil drain washer and replacing it consistently, you protect your engine, reduce the risk of messy leaks, and improve the reliability of every oil change you perform.