* Chevrolet Express 1500: The base engine is a 4.3L Vortec V6
* Chevrolet Express 2500/3500: The base engine is a 4.8L Vortec V8
Keep in mind that these are the base engines, and different trims or options might have come with larger engines. For example, some models were available with a 5.7L Vortec V8 or even a 6.0L Vortec V8.
To be certain about the specific engine in your 2001 Chevrolet Express, you should check the vehicle's VIN (Vehicle Identification Number). You can find this on your vehicle's registration, insurance documents, or the driver's side doorjamb.