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Thermostat-is it time to replace it?

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Beagleman

Regular Contributor
Whats up guys. You guys are so awesome that I decided to hit you up for advice again. I got a 40 hp mariner (40 E 6E9 s 104752), 1985 2 cylinder outboard. Basically a copy of those old Yamaha fm series.

I was told to haul the thermostat to see if it worked by pushing in the spring, attaching a string, suspending it in water and seeing if it moves. I even waited for the water to boil, and I seen no change in the thermostat. Is it time to replace the thermostat, or am I doing something wrong? If I have to replace it, would someone mind showing me a link for the cheapest possible thermostat available?

I appreciate any help.

All the best.

RObby
 
If the thermostat never opens, it's definitely time to replace it. Although most thermostats fail open, I have seen a couple fail closed.

Thermostats are pretty cheap as it is...just find a part number you need and grab one somewhere. If you feel you need to price hunt, go ahead, but there probably won't be a huge difference in that market.
 
kimcrwbr1 said:
That is the thing with this motor they are not cheap.
Click to expand...

Amen to that. The one for my '82 30 HP is about $68 on-line (as a Mercury part). As noted, if you can get a cross-reference to a Yamaha part, you may save some $$$$ (BTW, if you do find a comparable Yamaha part # pls. post it here for others [or me, at any rate :)] ).
 
The manual says to do the spring test as you mentioned. You did the test and it failed. The manual says you have a bad stat. Get a new one and don't run without it as some parts of the cylinders could be out of the cooling water and get excessively hot.

Simple as that. I don't know why your stat would be any more expensive than the rest of them. They are all pretty much the same thing. I know my 90 hp and my son's 150 have exactly the same stat with the same opening temp of 143F. They probably sell them on here or there other places to get stats.....iboats, Mercury Marine, Crowley's to name a few.

Mark
 
It's worth it. A thermostat that old might test good, and then the next day fail on you in the engine. Replace it.
 
I recently replaced one that tested good, but found that if the center part were rotated to a certain spot, it would stick. If you end up needing one, here is the Yamaha number: 656-12411-01. It may be cheaper. My motor uses the same one, and I couldn't find it for under $50 US. If I did, they had the wrong part. You'll also need to get some gasket material from the parts store, and cut your own gasket. Clean your threads real good, and torque to 5lb/ft (less if you put anything on the threads).
 
Thanks to all of you guys. I was out fishing on my cousins trawler the last couple of day and never had a chance to reply.

I'm gonna put it back together today, and see how it works. If the stat is bad, until I get a new one, I shouldn't run it, or should I?

Robby
 
Just to see if the pump is working? You'd have to put the thermostat cover back on, right? If you've decided to replace the thermostat, why don't you wait until that's done? If you run it with out a thermostat, it won't get up to temp. Running it too long like that will likely foul your plugs out.
 
Beagleman said:
If the stat is bad, until I get a new one, I shouldn't run it, or should I?

Robby
Click to expand...

Re-read my post. I told you Mercury Marine aka Mariner said that your stat was bad. A bad stat, stuck shut as yours, will cause you all kind of serious engine problems, mainly in the cylinders, rings, and pistons.

Look on the bottom of the copper pellet on the bottom of your stat and see if it doesn't say 143. It happens to be the same stat that is in my 2002 90 hp Merc. and a lot of other Mercs/Mariners. The other popular stat they use is a 120 degree stat and it is used on small engines 6 to 30 hp.

If you will take the time to go to the top of this page and put your engine serial number in as they ask for outboard, Mariner parts, it will walk you through the process. Or just plug in 75692, or Sierra's pn 18-3553 and see your stat.....about $10 big deal. If you have an odball 130 degree stat it is on the same page but out of stock for twice the price.

Or if you can't get that to work, go to iboats site and click on Forums and at the top of the page Boat Motor Parts and walk through it via Mariner, then your HP you will come to your stat made by Sierra, PN 18-3553, for $10 also. It's a 143F opening temp stat.

Mark
 
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Texasmark said:
a lot of other Mercs/Mariners. Mark
Click to expand...
Mark,you are correct but this is a Yamaha Mariner,which is just an older Yamaha outboard painted in Mariner colours ,not the Merc built version.And the stat comes in at $50+,but the Yamaha equivalent comes in under $30
656-12411-01 that H.I.McDunnagh gave you is the correct number,it supercedes the one I gave you.
 
I just put your stat p/n into the Google online search engine. Got numerous answers. Looking over some of the Yammie stats, I can't see what can possibly make them so expensive. They appear to be just like all the rest: A pellet to average out the heat, a thermally sensitive spring, a valve attached to the spring and either a flat circular mounting surface or one with a rubber gasket around it. Only real difference I can see is their opening temps are much lower than Mercs.

So I went to Sierra via Google and pulled up their complete online catalog. No help there either.

This is my first experience with Yammie parts. If all their stuff is this high, I surely don't want to leave my Merc. and go with them.

Mark
 
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