What Size Is the Oil Drain Plug on an Audi?

Most modern Audi models use an oil drain plug that takes either a 19 mm socket or an 8 mm internal hex (Allen) key, but the exact size and thread vary by model, engine, and whether Audi uses a metal bolt or a plastic drain plug. To avoid stripping threads or causing leaks, owners should confirm the exact spec for their specific car using the VIN and official documentation rather than relying on a single universal size.

Why There Is No Single “One-Size-Fits-All” Audi Drain Plug

Audi builds a wide range of engines across sedans, SUVs, coupes, and performance models, and each powertrain can use a different oil pan design and drain system. Over the past decade, the company has also shifted many engines from traditional metal bolts to plastic “service” drain plugs intended to be replaced at each oil change. As a result, asking for “the Audi oil drain plug size” without specifying model and engine will produce only approximate answers, not precise ones.

Typical Audi Oil Drain Plug Head Sizes

While thread dimensions can differ, the external head or drive size Audi uses for drain plugs is fairly consistent on many models. These are the sizes Audi and VW enthusiasts most frequently encounter during oil changes.

• 19 mm hex head: Very common on older and some current metal drain bolts for longitudinal engines (e.g., many older A4, A6, A8, some Q5/Q7) where a regular 19 mm socket fits the bolt head.
• 8 mm internal hex (Allen) plug: Used on many 2.0 TFSI and TDI engines and some later designs, where the drain plug is recessed and removed with an 8 mm Allen bit.
• 6 mm internal hex: Seen on some smaller engines or secondary plugs, particularly in older models or specific oil pan designs.
• Plastic twist-lock plug (no traditional hex head): Newer EA888 and other MQB-related engines may have a plastic drain plug that uses tabs or a molded profile, often removed with a Torx or flat-blade driver, or a special plastic plug tool.

These head sizes reflect what tool you’ll need to remove the plug, not the thread size itself. They are the most common across the lineup, but exceptions exist, especially on performance models and diesels.

Common Thread Sizes Used on Audi Oil Drain Plugs

Beyond the tool size, the thread specification is what matters for buying a replacement drain plug or installing a new oil pan. Audi (and parent group Volkswagen) predominantly use metric threads standardized across families of engines.

• M14 x 1.5: One of the most widely used thread sizes on VAG (VW–Audi Group) engines for traditional metal oil drain bolts. Seen on many older petrol and diesel engines and still present on various current models.
• M16 x 1.5: Used on some larger engines or specific oil pans, particularly in higher-displacement V6/V8 engines and certain diesel applications.
• Proprietary plastic plug dimensions: Modern plastic drain plugs generally match the thread in the plastic or aluminum pan but are sold as application-specific parts rather than by a simple thread size. They usually include an integrated O-ring and are designed for one-time or limited re-use.

Because Audi shares many engines with Volkswagen, Skoda, and SEAT, these thread sizes often match across brands, but you should still cross-check the part number for your specific vehicle.

How the Size Varies by Audi Model and Engine

Different Audi ranges and engine families tend to cluster around specific drain plug designs. Understanding roughly where your model falls can help you narrow down what you’re likely to find under your car.

Small and Mid-Size Petrol Models (A3, A4, A5, Q3, many 1.8/2.0 TFSI)

For compact and mid-size petrol Audis, particularly those using 1.8 or 2.0 TFSI engines, several recurring patterns appear in real-world servicing and parts catalog data.

• A3 / S3 (8P, 8V; 1.8T, 2.0 TFSI): Commonly use an 8 mm internal hex drain plug, often with an M14 x 1.5 thread for metal pans. Some later MQB-based A3s with plastic pans use a plastic service plug instead.
• A4 / A5 (B7, B8, B9 2.0 TFSI): Frequently feature an 8 mm Allen plug, with M14 x 1.5 threads on metal pans. Newer B9 engines may use a replaceable plastic plug that’s supplied as a specific Audi part.
• Q3 (2.0 TFSI): Similar to the A3/A4 in hardware: typically an 8 mm internal hex plug, often M14 x 1.5, unless a plastic pan is fitted.

In this segment, a mechanic’s go-to tools will almost always include a 19 mm socket and 8 mm Allen socket, covering the vast majority of drain plugs encountered in day-to-day servicing.

Diesel Models (TDI Engines Across A3, A4, A6, Q5, Q7)

Audi diesel engines (TDI) share much with VW counterparts and thus rely heavily on the group’s standard drain bolt designs, with some variations for displacement and pan material.

• Small TDIs (1.6 TDI, 2.0 TDI): Most commonly use an 8 mm internal hex plug with M14 x 1.5 threads for metal pans.
• Larger TDIs (3.0 TDI V6, older 2.5/2.7/3.0 units): Often step up to M16 x 1.5 metal bolts, with a 19 mm hex head in many cases.
• Later TDIs with plastic pans: May use plastic replaceable drain plugs, sold by Audi under specific part numbers and removed with Torx or Allen bits depending on design.

Because diesel engines can see higher crankcase pressures and harsher duty cycles, ensuring the correct thread and a fresh crush washer or O‑ring is particularly critical to prevent seepage.

Performance Models (S and RS Lines)

High-performance S and RS models often use larger or more specialized oil systems, but the drain plug hardware is still fundamentally similar to their mainstream siblings.

• S4 / S5 / S6 / S7 (V6 petrol): Frequently use a conventional metal oil drain plug with an M14 x 1.5 or M16 x 1.5 thread and a 19 mm hex head, sometimes with a captive or separate crush washer.
• RS models (e.g., RS3, RS4, RS5, RS6): Use application-specific plugs that are often still M14 or M16 threaded, but their exact head profile and washer type should be checked against the factory part number.
• Older performance engines (V8, V10): Typically have traditional metal plugs, 19 mm hex, with larger threads (commonly M16 x 1.5), though some may feature multiple drains for complex sumps.

Because performance engines can be more expensive to repair and sometimes run lower ground clearance, mechanics are especially cautious not to over-torque or strip these plugs, making accurate size and torque information essential.

SUVs and Larger Models (Q5, Q7, Q8, A6, A7, A8)

Larger vehicles share engines with sedan and coupe relatives but may have different oil pan geometries or underbody shielding, which affects access but not always the plug size itself.

• Q5 (2.0 TFSI / 3.0 TDI): Typically uses the same plug dimensions as equivalent A4/A6 engines—commonly 8 mm internal hex on 2.0 petrols and 19 mm hex on some V6 diesels.
• Q7 / Q8 (V6 petrol/diesel, V8): Often use larger M16 x 1.5 threaded bolts with 19 mm heads, but plastic pans and service plugs appear on newer engines.
• A6 / A7 / A8 (various petrol and diesel engines): Behind undertrays, you’ll usually find standard VAG hardware: either 8 mm internal hex or 19 mm hex head, with M14 x 1.5 or M16 x 1.5 threads depending on engine family.

Because underbody panels can hide the pan, DIY owners sometimes discover the plug type only after removing several covers, underscoring the value of confirming the correct replacement parts beforehand.

Factory Torque Specs and Washer Types

Knowing the head and thread size is only part of a safe oil change. Torque and sealing design are just as important to avoid leaks or damage to the aluminum or plastic oil pan.

• Typical torque values: Many Audi metal drain bolts are tightened to around 25–30 Nm (18–22 ft‑lb), but exact torque varies by engine. Some plastic plugs have even lower torque specs and can crack or deform if overtightened.
• Crush washers: Metal bolts usually seal via a replaceable aluminum or copper crush washer. Audi often specifies replacing the washer at every oil change to maintain proper sealing.
• Integrated seal plugs: Many plastic plugs contain a built-in O‑ring or rubber seal that is not separately serviced; the entire plug is replaced instead.

Correct torque and fresh sealing components matter more than the plug size itself. A properly torqued, correctly sealed plug of the right specification dramatically lowers the risk of oil loss or future pan damage.

How to Find the Exact Oil Drain Plug Size for Your Audi

Given the number of engine and pan variations, the most reliable way to determine the exact oil drain plug size for your Audi is to consult vehicle-specific information sources rather than rely on generalizations.

• Owner’s manual and service manual: Many Audi manuals list the type of plug or at least the required part number and torque values, which you can then cross-reference to determine size and washer type.
• VIN-based parts lookup: Audi dealers and reputable online parts catalogs (using your VIN) can pull the exact drain plug part number and specify whether it is metal or plastic, its thread, and the associated washer.
• Existing plug inspection: If safe to do so, you can remove the current plug and measure it directly with a caliper: gauge the thread diameter (e.g., ~14 mm for M14) and pitch (e.g., 1.5 mm), and note the head size (19 mm hex, 8 mm Allen, etc.).
• Service bulletins and technical documents: For newer models, Audi sometimes issues updated part numbers for improved plugs or revised torque specs. Checking recent technical information can reveal if the original plug has been superseded.

Using these sources ensures that the replacement plug matches the engineering intent of your specific Audi, helping avoid thread mismatch, leaks, or pan damage that generic “fits Audi” parts might cause.

Practical Tools to Have Before Changing Oil on an Audi

Owners who perform their own maintenance can minimize surprises by preparing a basic toolkit that covers the most common Audi drain plug configurations.

• Socket set with 19 mm socket: Covers most metal hex-head drain bolts across older and many current engines.
• Metric Allen (hex) bit set (up to at least 8 mm): Essential for internal hex drain plugs widely used on 1.8/2.0 TFSI and TDI engines.
• Torx bits and flat-blade screwdriver: Useful for plastic service plugs and underbody panel fasteners.
• Torque wrench (low-range capable): Allows tightening to the manufacturer’s specified torque rather than guessing and risking overtightening.
• Crush washers or new plastic plug: Always have a new sealing washer for metal bolts or a new plastic plug on hand before starting the job.

Equipped with these tools and parts, most DIYers will be able to handle the majority of Audi oil drain plug designs they encounter, provided they verify the exact type beforehand.

Key Takeaways on Audi Oil Drain Plug Sizes

Although owners often search for a single number, the reality is that Audi uses several plug configurations, and the only precise answer is the one matched to your specific car.

• Most modern Audis use drain plugs driven by either a 19 mm socket or an 8 mm internal hex (Allen) key.
• The most common thread sizes are M14 x 1.5 and M16 x 1.5 for metal plugs, while newer plastic plugs are application-specific service parts.
• Small and mid-size petrol and diesel engines typically use an 8 mm internal hex plug (often M14 x 1.5); larger and performance engines more often use 19 mm hex-head bolts with M14 or M16 threads.
• Plastic drain plugs with integrated seals are increasingly common and should usually be replaced at each oil change rather than reused.
• The safest method is to confirm the exact plug size and type using your VIN, owner’s manual, or an official Audi parts catalog before performing an oil change.

By recognizing that “Audi oil drain plug size” is not universal and verifying the exact specification for your model, you reduce the risk of leaks, stripped threads, or expensive oil pan replacement, ensuring a clean and reliable oil change every time.

Summary

Most Audi oil drain plugs require either a 19 mm socket or an 8 mm Allen key, with M14 x 1.5 and M16 x 1.5 being the most common thread sizes, though many newer engines use application-specific plastic plugs instead. Because Audi’s plug dimensions vary by model, engine, and oil pan material, the only reliable way to know your car’s exact drain plug size is to check your owner’s manual, consult a VIN-based parts catalog, or inspect the existing plug and its markings directly.