Replacing the thermostat on your Evinrude outboard motor isn't rocket science. Have a socket wrench, an adjustable wrench and a Torx screwdriver with you when you go in. Once you find and remove the cover, replacing the thermostat requires only that you note the orientation of the veritherm - whether it's pointing forward or aft as you remove it -- and that you return everything to the cavity in the reverse order of its removal.
5- and 6-Horsepower
The thermostat covers all smaller Evinrudes, those under 15 horsepower are held in place by two or possibly three 1/2-inch Torx bolts, requiring a Torx drive for removal. The covers of most 5- and 6- and some 8-horsepower motors are small and irregular, located on top of the cylinder head and face aft, On some 5- and 6-horsepower units, the cover is round and is located at the top-rear of the intake manifold, on the port side of the cylinder head.
8-, 9- and 9.9- to 15-Horsepower
For motors between 8- and 9-horsepower, the thermostat cover is round; on some models it's found atop the rear of the intake manifold on the port side of the cylinder head and is held in place by two Torx bolts. The shape and method of mounting change, however in the 9.9-horsepower motor. On 9.9- to 15-horsepower motors, the cover is rounded but irregularly shaped, and held in place by either Torx bolts or 1/4-inch bolts that can be removed with a socket or a small adjustable wrench. The cover is located either on the top, rear of the intake mainifold on the port side, or found on the top rear of the cylinder block on the starboard side.
40-Horsepower and Larger
On 40- and 50-horsepower motors, the cover is irregularly shaped. Held in place by 1/4 inch bolts, it's located on the top of the cylinder head, hiding just behind the engine-lift bracket. Because two of the bolts are on the edge of the cover nearest the lifting bracket, use a socket and extension to remove these. On 70-horsepower and larger motors,, the cover is round and secured by three 1/4-inch bolts. Located on the aft, starboard top side of the cylinder block, the cover is behind the engine-lift bracket, but far enough behind the lifting bracket that you can effect removal with your choice of a socket or a small adjustable wrench.
There's no thermostat cover for the 18- to 35-horsepower Jet motors. The bottom of the cylinder head cover serves that purpose, instead. When remove the cylinder head cover, look out -- there's a spring beneath the cover that pushes up on the cover and down on the thermostat, to keep the thermostat in place. The spring will jump out of the cavity unless your remove the head cover slowly enough to allow the energy in the spring to dissipate. When it does so, it's likely to take the rest of the thermostat with it.
- Seloc: Mercury Mariner Outboards 2.5-275HP 1990-2000 Repair Manual 2 Stroke, Including Fuel Injection & Jet Drives