Thermostat Change in 71 Evinrude 50hp

[71erude]

I recently came into posession of what i'm told is a 1971 Evinrude 50hp (50173S) -- I'm told it sat for several years (4-5) since being used, but that the last time it was used it "ran great."

I've been systematically going through several steps to bring the motor back.

-Carb Kits on both carbs
-Spark Plugs
-Inspected fuel pump
-Clean everything up (a family of roaches had been living in it)
-Lube everything up (starter, throttle linkages, etc.)
-Clean all the electrical connections (remote unit, powerpack connections, etc)

Well, yesterday I finally got to where I was ready to start it. I set it in a tank and it came right to life and idled nicely. The electric shift worked for both forward, reverse (and neutral).

Only problem: It overheated (hot horn worked) -- So I pulled the lower unit and i'm going to change the water pump housing and impeller. I also want to change the thermostat but the SELOC manual i'm using makes limited to no mention of how to do it. Does anyone have experience changing the t-stat on this year and model. From parts diagrams I'm guessing that it's located at the bottom of the back of the powerhead (where the spark plugs are) and that that whole cover has to come off?

Any help is greatly appreciated. Also, any pointers on what else I should service (i'm going to change the lower unit oil, special type-c oil for e-shift.)

 

[ezeke]

Re: Thermostat Change in 71 Evinrude 50hp

You have to remove the water cover from the cylinder head to service the thermostat. The thermostat is a standard 143 degree part. You will likely need to replace the cover gasket. There are 14 screws.

The oil for your gearcase is OMC/BRP Premium Blend.

 

[71erude]

Re: Thermostat Change in 71 Evinrude 50hp

Thanks for the info, was I correct in assuming where it was? The back of the engine (spark plug side) towards the bottom, that entire cover has to come off.

 

[ezeke]

Re: Thermostat Change in 71 Evinrude 50hp

I would leave the cylinder head in place and just remove the cover if you can reach all of the screws. The cover has to come off. Remember that the cover has a spring behind it when you open it up.

 

[EN2]

Re: Thermostat Change in 71 Evinrude 50hp

Not to offed Ezeke, but the spring is behind the pressure relief valve,that sits in a grommet in the cyl head.

 

[EN2]

Re: Thermostat Change in 71 Evinrude 50hp

Not to offend ezeke, the spring under the cyl cover is for the pressure relief valve ,which fits into valve grommet.

 

[EN2]

Re: Thermostat Change in 71 Evinrude 50hp

Not to offend ezeke, the spring under the cyl cover is for the pressure relief valve ,which fits into valve grommet.Fits into cyl head.

 

[EN2]

Re: Thermostat Change in 71 Evinrude 50hp

I have changed this cover before, bottom bolts are kind of hard to get to. Make sure top of head and cover surfaces are clean. Use OMC Gasket sealing compound. On this old of an engine slowly work cover bolts back and forth,do not force them. Use some kind of spray lube on the threads . These are good engines .I have used several of these crates over the years lots of power for their size.

 

[71erude]

Re: Thermostat Change in 71 Evinrude 50hp

thanks for the info, all, i'm going to try and pull this cover tonight and see if I can get the t-stat replaced. I've got a replacement cover gasket on order, will I still need to use the gasket compound with a new gasket?

Also, I feel like the water passages might be clogged up somewhere, i'm hoping just at the thermostat, but anyone have any recommendations on how to flush the system out most effectively?