1985 Mercury 50 HP Thermostat replacement Serial # 0A981915

[jhawknz@gmail.com]

I have a 1980's Mercury 50 HP engine. I also have a power head from the next year that is also a 50 HP Mercury. So, I rebuilt one while the other power head has a hole in one of the piston heads. Long story short I was salvaging this head while rebuilding the other motor. I found a thermostat and poppet valve in the salvage power head. It got me to thinking that I should look into my rebuild and see if that motor needed a new thermostat. In the rebuild the pee hole was really clogged. I have done a complete service of the lower unit. In the rebuild power head there wasn't a thermostat or a poppet valve. So, my questions is do I put one in? Or, should I not? What year did Mercury start using thermostats? I thought is that it would cold start without a thermostat? And, the design obviously looks like Mercury designed it to have a thermostat and a poppet valve. Curious if anyone knows the answer to this. I can't find anything in manuals or online that answers this question.

 

[SoCalBoatGuy]

I have an 87 50hp 3 cyl and it does not have a poppet or thermostat. It looks like there is place to put one, but nothing is inside.

 

[lmuss53]

Look in the parts blow up here or at another parts retailer, If it is listed in the parts for your year, I would put it in. A lot of these motors won't run right if they don't come up to the appropriate operating temperature.

 

[jhawknz@gmail.com]

That's sort of what I thought. I didn't see one on the Mercury site. I'll keep digging.

 

[jimmbo]

A 1985 50hp is a 4 cylinder block, and it does not have a Thermostat.

 

[lmuss53]

Go to the top of this page and click on "boat parts and accessories", find the Mercury parts and enter your serial number. If it calls for the t-stat and poppets, I would put them in.

 

[jhawknz@gmail.com]

So, I looked on Mercury's site and went through the various 3 cylinder engines in the 50 HP range. I couldn't find a thermostat or Poppet Valve. But, I did find a 70 HP that was a 3 cylinder and it shows the thermostat and poppet valve. Seems odd to me? Can anyone explain this?

 

[jhawknz@gmail.com]

Just to follow up on this thread. I found out from a Mercury guy that as Mercury built these engines they were designed and then changes were made as they went. So, its perfectly fine to run my engine with out a poppet valve and thermostat in this particular engine. But, if I were to run this in cold water I would have issues. So, the Mercury guy suggested putting a poppet valve and thermostat in. So, I've done that and it runs great.