What thermostat? What temperature?

[ethan169]

My boat:
1985 Wellcraft Scarab I
Originally equipped with a Merc 260 alpha 1 gen 1 combo. The engine has been replaced with a GM goodwrench crate 350 and many parts from the merc 260 were transferred to the new block. This is how I bought the boat.

For the people that don't like to read the detail --> My actual question is; What thermostat should I be running? It turns out its not very clear...

The details. I got the boat at the end of the season last year and took it on a quick lake run to see what was needed. The temperature had bothered me a little as it was ranging from 170-190F. I just completely resealed the upper gear housing and replaced the entire water pump in the lower unit with a sierra kit. I replaced the base, housing and impeller. Of course the gaskets and plates etc were replaced too. I looked at the thermostat that was on the engine and it appears to be a 160?F thermostat. Now I have seen people say Mercury recommends running 142? t-stats and others say 160? t-stats. I know that if the engine was in a car or truck it would most likely have a 180 or 193 t-stat or something like that.

Now my boat has through hull exhaust only so there is no need to worry about melting parts in the outdrive as the exhaust is not routed through that. Obviously the exhaust does still encounter the risers etc so maybe the temperature is lowered by design for one of those components?

I put the t-stat that I have in a pot of water and observed the temp that I start to see activity. Its about 175?F by the time its really open. It does seem to start opening around 160 though. I was always told thermostats are designed to fail open. But can they fail in a manner where they are slow to open? I've never really replaced a thermostat on a car/truck because the car was not getting to operating temp. Usually it would overheat during idle and during cruise with more water pump pressure it was better. Or it was just overheating all the time.

Thermostats are cheap and I should just replace it. Fine.. but which one SHOULD it be? What do other people with GM 350's in their boats run? There's gotta be a whole mess of people with this super common setup? Why is there so much controversy over it?

Also where do I get a new brass retainer? Ive included a picture of what I have for a thermostat and retainer.



Thanks for any info/help!

Ethan

 

[HT32BSX115]

Re: What thermostat? What temperature?

Now I have seen people say Mercury recommends running 142? t-stats and others say 160? t-stats.
Thermostats are cheap and I should just replace it. Fine................................................ but which one SHOULD it be?

Thanks for any info/help!

Ethan

Howdy,


You're right. Mercury suggests 140 for "normal" operation (160 for most closed cooling applications)

The temp is mainly aimed at salt water operation and higher temps will exacerbate mineral precipitation in the cooling system.

If you're operating in NON-salt water, you can get away with using a 160.

It does seem to start opening around 160 though.

That's exactly what it's supposed to do.


Regards,


Rick

 

[Don S]

Re: What thermostat? What temperature?

You can get the sleeve from your local Merc dealer or any online parts that sell Oem parts. It's not an aftermarket part.

Look at items 5 and 7 for the part numbers and temp for the stat (143?)

The picture came from the dealers program.

 

[ethan169]

Re: What thermostat? What temperature?

Thanks for the replies. I do run the boat in fresh water mostly. However I would like to be able to take it off shore with a few buddys that a have a boat out towards boston harbor. So I would like to be able to do that without worrying about the t-stat and salt water.

Here is where I get confused agian. This is the sierra replacments for the merc thermostat listed above (Merc 59137) Sierra 18-3551
Here is the link form amazon http://www.amazon.com/Teleflex-Marine-18-3551-Thermostat/dp/B00027GZXW/ref=sr_1_1?ie=UTF8&qid=1369083466&sr=8-1&keywords=18-3551#productDetails I have a prime membership so its nice to get things basically next day for free.

In the amazon listing it mentions

SIE 3552 is 160 degree thermostat for fresh water cooling only
Alternate part numbers: Sierra 8-3551, SIE_3551, SIE-3551, SIE3551, 47-3551

Why 160 degree? Typo? why fresh water use only? Because of the type being 160?

Thanks again.

 

[Don S]

Re: What thermostat? What temperature?

On the newer motors, Merc went to a 160? thermostat, but did not change that on the older models. Materials used in the engine different? Who knows, but they didn't change to 160 on the old motors. It all stayed the same.
Why don't you just get the correct Merc thermostat and quit worrying and wondering why the aftermarket suppliers decided to do something different. They sure don't ask this forums permission to do something different from the OEM, nor do they tell us why they do. Maybe because they don't know what they are doing ??????

 

[HT32BSX115]

Re: What thermostat? What temperature?

Thanks for the replies. I do run the boat in fresh water mostly. However I would like to be able to take it off shore with a few buddys that a have a boat out towards boston harbor. So I would like to be able to do that without worrying about the t-stat and salt water.

Here is where I get confused agian. This is the sierra replacments for the merc thermostat listed above (Merc 59137) Sierra 18-3551
Here is the link form amazon Teleflex Marine 18-3551 Thermostat : Amazon.com : Automotive I have a prime membership so its nice to get things basically next day for free.

In the amazon listing it mentions

Why 160 degree? Typo? why fresh water use only? Because of the type being 160?

Thanks again.

They mean 160 for "Fresh Water Cooling" [Closed cooling]

Just get the 142 degree stat and go boating.

 

[ethan169]

Re: What thermostat? What temperature?

Its a pretty simple device. Why would you say that the aftermarket companys dont know what they are doing? Besides If I wanted to buy the actual mercury part (59137) from this site it seems that not even an option. Only Sierra and Mallory are carried.


I appreciate your responses and information but I don't understand why people get all fired up about asking questions on a forum. Isn't that what forums are for? Another thing to add to that is having an questioning attitude its seems that fires people up too. I really don't see the reason for it. Its almost like "well the manual says THIS so do THIS and THIS only or else total destruction WILL happen!" Sure it might be true for critical components but you cant tell me that at least 75% of people are running aftermarket thermostats and have no problems. Again it is a fairly simple device.

Anyway. Thanks again for the information.

Ethan

 

[ethan169]

Re: What thermostat? What temperature?

They mean 160 for "Fresh Water Cooling" [Closed cooling]

Just get the 142 degree stat and go boating.

Will do. I did ask the particular seller this question and they promptly got back to me with this.

Amazon takes listing details from merchants but doesn't verify them. Sometimes this is a problem.
Sierra says this is a 142 degree thermostat and shows no restriction for fresh water.
Their only spec says
For: CH190/220-305ci, CH270-350ci, CH350-454ci, Ford 302/351 CID Engines
-
ShipStore Customer Service

So it seems there was just an error

Thanks again

 

[Don S]

Re: What thermostat? What temperature?

Its a pretty simple device. Why would you say that the aftermarket companys dont know what they are doing? Besides If I wanted to buy the actual mercury part (59137) from this site it seems that not even an option. Only Sierra and Mallory are carried.
View attachment 194733

I appreciate your responses and information but I don't understand why people get all fired up about asking questions on a forum. Isn't that what forums are for? Another thing to add to that is having an questioning attitude its seems that fires people up too. I really don't see the reason for it. Its almost like "well the manual says THIS so do THIS and THIS only or else total destruction WILL happen!" Sure it might be true for critical components but you cant tell me that at least 75% of people are running aftermarket thermostats and have no problems. Again it is a fairly simple device.

Anyway. Thanks again for the information.

Ethan

Then just do what you want, like I said before, no one knows why the suppliers do what they do. Lots of people like to guess and act like they know, but they don't. So does wrong answers help you make a decision?

Use the 160? in salt water if you want, just report your findings in a few years when the results are in. And be certain to include what happens with a 143? stat under the same conditions. Then you will have an answer worth reading.

 

[achris]

Re: What thermostat? What temperature?

The main reason for a lower thermostat in salt-water is because at higher temperatures salt water disassociated into hydrochloric acid. Something you don't necessarily want in your exhaust system, especially with all those aluminium parts.

The OEM manual states 143 degrees, use that. If Sierra and Mallory want to tell you to use a different temperature to what the ENGINE MANUFACTURER says, ignore them, they are NOT Mercury marine and don't have a full blown R&D team working out these design items. (cavert: Don's "why the design team was sent home" poster)....

Chris.....

 

[ethan169]

Re: What thermostat? What temperature?

The 160? listing was a type. It is indeed a 143? t-stat. And as for the fresh water cooling i beleive HT32BSX115 is correct on the way they worded it.

Don I never mentioned that I wanted to run the 160? in salt water. Quite the opposite I wanted to figure out why I have the 160? t-stat in my boat and weather or not i should replace it with the 160 or use the 143 that I see some people using. The fact is that I researched it a bit and I saw lots of people saying that 143 was what merc designed it for so use that one. However almost an equal amount of people said the same thing about the 160 t-stat and that is what it was designed for. As you mentioned the original design was for a 160 version and it was later discovered that the 143 was a better fit or required for salt water use. So the "newer" generation motors had the 143? spec. So both side are kind of right but I see now that the 143 is the better option..

I wanted more information then just "yeah use the 143 because I have been doing that for 25 years and not a problem. Trust me I know what im talking about because i have 300,000 posts and thats proof enough." Its not for me... If there are facts associated that make sense then sure Ill buy it. Which is what I got here...

Anyway... Thanks again for all the help and information. Im fully convinced.

Ethan

 

[achris]

Re: What thermostat? What temperature?

This is a grab from the MERC genuine service manual, section 6A, page 2 if you'd like to check. This should be the end of the discussion.....

 

[ethan169]

Re: What thermostat? What temperature?

I'm sorry if my tone came across sarcastic. I was indeed fully convinced about the 143 degree tstat. However I do appreciate you posting the screenshot from the manual Chris.

 

[achris]

Re: What thermostat? What temperature?

I'm sorry if my tone came across sarcastic. I was indeed fully convinced about the 143 degree tstat. However I do appreciate you posting the screenshot from the manual Chris.

No Problem... One more thing I would add, is that just because you found a 160 thermostat in there doesn't necessarily mean it's the right one. Maybe some smart-arse in the past (prior to you owning the boat) thought he knew better than the people who made the engine (plenty of them around :facepalm and put it in. Or, the boat was used in fresh water only prior to you owning it..... Or, they have a seloc or clymer manual....

All of the above is why I only ever use genuine manuals when working on anything.... (and you should see some of the manuals I have to work with. I wish they were all as good as the Merc manuals)...

Chris.........

 

[ethan169]

Re: What thermostat? What temperature?

No Problem... One more thing I would add, is that just because you found a 160 thermostat in there doesn't necessarily mean it's the right one. Maybe some smart-arse in the past (prior to you owning the boat) thought he knew better than the people who made the engine (plenty of them around :facepalm and put it in

Agreed. This is exactly why I questioned it to begin with.

 

[ethan169]

Re: What thermostat? What temperature?

Ok this really shouldn't be that complicated but there is SO much conflicting information out there..

I have the new t-stat and gaskets. I also purchased a new mercury brass sleeve. When I took the housing apart the thermostat was in the bottom of the housing and the sleeve was holding it in with the lip facing down touching the t-stat. There was no cork gasket.

Im reading through manual #9 for my engine type mid to late 80's merc 260. It shows the sleeve going in first with the lip facing up and then the t-stat with the cork gasket below the t-stat.


But from what I can see most people are placing the t-stat first then the cork gasket then the spacer?

Which way is it really supposed to go? If I follow the manual its different then how EVERYBODY seems to do it. Don I looked at numerous posts where you responded and mentioned the t-stat then cork then sleeve and "crush" the sleeve down. This isnt what the manual says? If it has changed over the years fine Id just like to make sure its in the proper configuration.

I really appreciate your help on this!

 

[Don S]

Re: What thermostat? What temperature?

But from what I can see most people are placing the t-stat first then the cork gasket then the spacer?

Do all those people have the same thermostat housing you do? Not all go together the same way or in the same place.

Install it as shown in the manual, FOR YOUR TYPE THERMOSTAT HOUSING, and it will be right.
Maybe all those other people are doing it wrong because they don't know how to do it right.

 

[ethan169]

Re: What thermostat? What temperature?

Well I attempted to assemble the thermostat housing the way the service manual states but it just didnt look right. I could see that the t-stat housing cover just wouldn't seal right due to the brass retainer ring not being even close to flush with the gasket. I would have to gob a bunch of silicon/rtv type sealant there to make a seal and thats just not right. I assembled it the way I took it out of the boat and the way ive seen other t-stats of the same setup done. (t-stat - brass retainer - gasket - top cover) so I omitted the cork gasket. It just didnt fit correctly.

I ran the boat at idle at the local boat launch for the river and the gauge stays rock solid at (165-170?) I checked manifold temp at t-stat housing with an IR thermometer and it was 134-140? as expected. The risers stayed a cool 95? on to tops and on the sides were a touch warmer at 107? or so.

I had the boat out for half of the day on sunday for a test run and all seemed well. On monday it was a beautiful day and we took the boat to candled lake in south west CT and had it out all day with no mercy. The boat gave no issues whatsoever. Temperature was always good. Even my newly re sealed alpha upper managed to not grenade! I think the boat is ready for the season!

Thanks again Don, Chris and others for all of your help.

Ethan