1. Check the VIN (Vehicle Identification Number)
* Location: The VIN is usually located on the driver's side dashboard, near the windshield, or on the driver's side door jamb.
* Decoding: The 8th digit of the VIN typically indicates the engine code. You can use an online VIN decoder or a GMC service manual to find the specific engine associated with that code.
2. Check the Engine Block
* Location: The engine block itself will have a casting number stamped on it.
* Finding the Number: You'll likely need to remove some components (like the air intake) to see the casting number clearly.
* Decoding: Use an online database for casting numbers (like a parts website or a GM service manual) to identify the engine size.
3. Consult the Owner's Manual
* If you have the original: The owner's manual for your truck should have detailed information about the engine, including its size.
4. Look for Engine Identification Tags
* Location: There might be a metal tag attached to the engine block or firewall that lists the engine details.
5. Contact a GMC Dealership or Mechanic
* Information: They can often use your VIN to retrieve information about the original engine size.
Common Engine Sizes in 1979 GMC Trucks
* V6: 4.1L (250 cubic inches)
* V8: 5.0L (305 cubic inches)
* V8: 5.7L (350 cubic inches)
* V8: 6.6L (400 cubic inches)
* V8: 7.4L (454 cubic inches)
Important Note:
If the truck has been modified, the engine may not be the original. You may need to use a combination of the methods above to determine the engine size accurately.
