model year of my 20 hp Mercury

[roy481]

recently purchased a boat that came with a Mercury 20 HP motor. the owner did not know th eyear of the motor. he was selling the boat for his dad's estate. the only number I can find on the morote is OB339613. this is on a plate that is attached to the side (oposite of the tiller arm side) of the lower unit right at the transom mount.

Not sure if this is the right number or not.

Tried to look it up on several web site but to no avail.

I am trying to learn the year so I can get an owners manual and serivce manual for it.

I want to test the motor. I know it cranks. I do not know where to locate the "pissrer" for the water pump. Is it on the side of the engine, back of engine not sure. do not want to ruin the motor trying to find out.

any suggestions would be appreciated.

 

[achris]

Re: model year of my 20 hp Mercury

Take the cowl off the engine and look at the top of the cylinder head. You'll see the thermostat housing. On the thermostat housing is a hose. That hose is the telltale you're looking for.

1988.

Chris.....

 

[roy481]

Re: model year of my 20 hp Mercury

Thanks Achris. I appreciate the fast answer.

Am I to assume no water coming from this tube means. A) thermostat is bad and should be replaced, B) waterpump is not working or C) both thermostat and waterpump should be replaced.

 

[achris]

Re: model year of my 20 hp Mercury

When I buy a secondhand engine I assume it has never been serviced (and most of the time I'm right)... So I replace the water pump impeller, drain and refill the gear case, replace the spark plugs and thermostat, and check and adjust the timing and carb sync.

No water from the telltale, on those engines, could just mean the thermostat hasn't opened yet. If you need to check for water flow, with the engine running, touch the exhaust cover (port side of the engine block) with the back of your fingers. It should be cool. If it isn't, replace the impeller.

Chris.....

 

[roy481]

Re: model year of my 20 hp Mercury

Thanks again Achris

I will do all you suggeste