Where's My Thermostat?

[fishfetchr]

Hello- Where is my thermostat / thermostat housing located??
I have a 1986 Merc 200.
The motor suddenly stopped showing water from the telltale. and the overheat alrm came on so I shut down promptly. Lower Unit impeller was done late this spring, and the boat didn't run in the shallows where it could have picked up muck or damaged the impeller. I was told it could simply be the thermostat and this was easy to do. My manual doesn't seem to show the area of the motor that its mounted on, it only covers cleaning or testing it in boiling water.
I'd appreciate some insight.
Thanks.
Mario

 

[joblo33]

Re: Where's My Thermostat?

I believe there's one on each head right above the upper spark plug hole.
Eric

 

[andy6374]

Re: Where's My Thermostat?

Yep, there's a thermostat housing at the top of each cylinder head. If you haven't replaced the tstats in awhile then don't bother testing them, just replace them. Best $20 you could spend.

 

[ncfish1]

Re: Where's My Thermostat?

Mario;

It would beneficial before reinstalling the new t'stats, to run the engine with the t'stats out. This will tell you if you have other problems in the water loop.

Simply remove the t'stats, install the water ears on the lower unit, start the engine and allow to idle. You should have a "steady" stream of water from both t'stat ports. Tape plastic just below the ports to divert water from soaking the heads.

You shouldn't have to run the engine for more than a few minutes before water starts coming from the ports. This in no way harms the engine as long as you do not over-rev it for an extended period.

If you find little or no water from either port, then your problem is elsewhere.

Capt. Mike

 

[Texasmark]

Re: Where's My Thermostat?

Thanks Capt. Have ordered new stats for the boy's 150 and will follow your suggestion prior to installing them. So you helped me too. d

Mark

 

[fishfetchr]

Re: Where's My Thermostat?

Thanks!

 

[Texasmark]

Re: Where's My Thermostat?

Well, yesterday most of the family headed back for home (except for one) and we modified his cooling indicators.

Just as I said we would do, we removed the tee from the stat outputs that went to the pee spiggot and relocated it in the line I mentioned that comes out the top center of the block. Stuck a barrel union in place of it in the stat line.

Sure nuf, when the block filled with water, the pee came out nice and steady and responded to changes in rpm's.

Then out came the stats and did a visual on the water passages which were immaculate...whoope!

Then did as Capt Mike suggested. Draped plastic on the engine, cranked her up and let her run.....crystal clear and plenty of it.

New stats aren't here yet but should be in today or tomorrow and we'll close her back up.

For the record, these stats were 143 F. I noticed, I think in iboats sales, where you can buy stats, that there are several temps available for this engine. Don't know what we are going to get.....just called the Merc dealer and said to send a couple. Hopefully he knows the right temp.

For the record, my 3 cyl 90 hp has a 120 in it (later year model). Guess actual temp is not all that important, different engines like different temps, or later on Merc decided to cool em off a tad.

One more tidbit. We have batted stats or no stats around on here numerous times. Yesterday I realized that, at least on Merc V engines, if you have no stat in the port bank (lower of the two) you cannot get overflow in the starboard bank at idle. That means that the top of the engine is without water as several have said would happen. Do you want that in your engine?

Run with your stats installed. d

Mark