What size is a GM drain plug?
For most GM cars and trucks, the oil drain plug head is a 14 mm hex with M14x1.5 threads. There are exceptions by model and year, and some transmissions use different plugs. Always verify with the vehicle’s service manual or OEM specifications for your exact year and model.
Common drain plug sizes on GM engines
The following reference captures the sizes you’re most likely to encounter when servicing GM engines. Use this as a starting point, but always confirm with the exact model year documentation.
- Oil pan drain plug head: 14 mm hex (socket size 14 mm). Thread: typically M14x1.5. This is the standard for most GM gasoline engines from the mid-2000s to today.
- Some older or specialty GM engines may use a different head size (for example, 13 mm or 15 mm) depending on the variant. Always verify against the service manual for your exact engine.
- Transmission pan drain plugs and certain non-standard applications vary widely across GM transmissions. Check the specific transmission manual or GM service documentation for the exact size.
In practice, 14 mm hex is by far the most common for GM oil pans, but there are exceptions. When in doubt, refer to the owner’s manual or the GM service manual for your model year.
How to verify the correct size for your GM vehicle
Use these steps to confirm the drain plug size without risking damage from an incorrect socket.
- Look up the OEM specification in the vehicle’s service manual or GM’s online service portal for your exact year and model.
- Inspect the drain plug head on the oil pan: if the head is worn, measure across flats with a caliper or ruler to determine the nearest standard size (commonly 14 mm, but other sizes exist).
- Test-fit a socket of the suspected size (start with the most common 14 mm) and ensure it seats fully without slippage or rounding. Do not force a larger socket.
- If you are replacing the plug, verify the thread size (M14x1.5 is common for many GM engines) and use a new OEM drain plug or a compatible aftermarket part with the correct thread engagement.
- When in doubt, contact a GM dealer or qualified mechanic with your VIN to confirm the exact plug size for your vehicle.
Correct sizing is essential to prevent leaks or thread damage. If the plug or pan shows signs of wear, replace the pan or use a new plug with the proper dimensions.
Model-specific notes
Modern GM gasoline engines (2000s–present)
For most modern GM gasoline engines, including many EcoTec and LS-family designs, the oil pan drain plug is a 14 mm hex with M14x1.5 threads. Always confirm with the service manual for any model-year variations or special editions.
Older GM engines and specialty applications
Some earlier GM engines and certain non-standard variants may use different head sizes or thread specifications. If your vehicle falls into this category, consult the specific repair manual or GM tech data for the exact drain plug size and thread pitch.
Summary
In the vast majority of GM vehicles, the oil pan drain plug uses a 14 mm hex head with M14x1.5 threads. Exceptions exist, especially with older models and certain transmissions, so always verify against the exact year/model service documentation. When servicing, rely on OEM specifications, inspect the plug and pan for wear, and replace with the correct part to maintain sealing integrity.
