See full version: How do I find out what year my Yamaha outboard motor is
Your Johnson outboard model number can usually be found on the nameplate located on the motor or the mounting bracket. The nameplate should contain a model number and a serial number. The model number will identify the year and certain details of that motor.
Consequently, where is the model number on a Yamaha outboard? here
Yamaha Outboard Serial Number Location and Model Identification. Yamaha Outboard Motor MODEL, PRE-FIX and SERIAL NUMBER'S are stamped on a metal plate which is mounted on the transom clamp bracket located at the rear of the boat.
The most common cause of outboard motor overheating is water pump failure. Water pump failure can also be caused by a defective heat exchanger, though this is harder to check. Generally, if it is not a problem with lack of raw water flow or fresh water, the heat exchanger will be the cause.
If it has a telltale, and there's water coming out, it ain't getting hot. If you stick your finger under the telltale water it should be warm, but not hot. If the motor has a thermostat, it will probably run a little hotter. here
Secondly, what would cause a boat to overheat? Overheating can also be caused by a worn or damaged water pump impeller. If the impeller is damaged and is missing a vane, make sure any displaced pieces are accounted for and removed. Any debris left in the water passages may reduce flow, which leads to persistent overheating.