Locate the engine block number by looking at the dashboard underneath the windshield in front of the driver's seat, according to eHow. On cars newer than 1981, the number will be 17 digits long. On cars older than that, the number will be 11 to 17 digits long.
If the engine block number is not found underneath the windshield in front of the driver's seat, it may be located on the inside of the driver side door. However, if it is not in either of those places, turn off the vehicle and open the hood, latching it into place with the support mechanism. Do not touch anything under the hood if the car has been recently running, as it may be very hot.
Leaning under the open hood, find the wide metal part, usually found directly in the center. That is the engine's top. On top of the engine, the engine number should be engraved into the metal.
If the number cannot be found in the above locations, check the car's registration, as it is required to include the vehicle identification number, or VIN. On the registration, it should be located near the top of the form, according to eHow.