Seems to be asked quite a bit so I thought I'd help a little in this regard. Don or Sherm might jump in on this but pictures speak a thousand words they say. Most know the most logical place is a plate on the motor
First one is more of a distance shot to give you an idea - most I know are on the starboard side of the motor
and a close up view of what that tag could look like (info on tag may vary)
and then if you can't find that - look for the welsh plug as it'll be stamped on it
Remember its Digit, Letter, 6 more Digits (except older motors) and rebuilt motor may not have the serial number.
Remember - Mercury DOES NOT go by year but by serial number when it comes to ordering parts etc.
Engine Serial Number
Table Of Contents
Mercury Engine Serial Numbers
Model Number and Serial Number These numbers are located on the transom bracket of the motor. Engine Cast Number. 3 CYL of L# Powerheads: Please provide the cast number for 70, 75, 80, and 90 HP powerheads built between 1987 and 2002. This number is located on the starboard side of the block next to the number 3 CYL. Example: 877 - 8946 - C7.
PLEASE NOTE: leading zeroes are not relevant, e.g. '0B123456' is the same as 'B123456' in the listing.
However, later model serial will begin with a '1' or higher in pace of the '0'; those ARE significant .
US-made Mariner motors are identical with Mercury serial number ranges and use these same charts.
The serial number format is the same.
Japanese Mariner motors have a totally different serial number scheme, e.g. '6A3-S-123456'
We currently do not have those here, but are largely useless. These motors do not have any consistent year-to-serial scheme.
Mercury ceased publishing this information after the 1996 model year. There is no way to find the model year of motors with significantly higher
serial numbers than listed in these guides. There is NO serial-to-year cross-reference chart for 1997 and later motors.
Mercury has never really used model years for much of anything other than 'sales tools' in dealerships.
We WILL need your serial number to look up correct parts.
Arranged by Horsepower
Mercury Outboard Motor Serial Number Lookup
4 - 6 HP
7.5 - 9.9 HP
15 - 25 HP
30 - 40 HP (2-CYL)
40 (4-CYL) - 50 HP
60 - 100 HP
115 - 150 HP
175 - 300 HP
SPECIAL HIGH-PERFORMANCE OUTBOARDS