# Thermostat change



## ch53joe (Apr 9, 2008)

Had boat in for spring servicing at Marine Max on Airport in PNS. When testing the boat after the impeller change, they informed me that my thermostat was discovered stuck open and needs to be replaced for $150. They said if it wasn't changed that the engine would run cool (recommend 160 degree) and this would cause the fuel mix to be rich.

I told them that I would bring it back, but wanted to do some research to see if this could be easily done by myself for less than $150.

I saw in a forum where it is fairly common for a piece of an impeller to find its way to the thermostat, causing it to be stuck open. I am hoping that it just needs a good cleaning, and even if it does need a change, it looks to cost $25 and not the $150 that they tried to upsell me on.

Q's:

Where to start? How do I locate the thermostat on this Merc Cruiser 350 i/o on my 199 21' Sea Ray Sundeck? Any suggestions on things to avoid when cleaning/changing the item?


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## H2OMARK (Oct 2, 2007)

Last time I checked the thermostat wasn't but about $12.00. Before taking it to Marine Max, I would contact either three of the marine guys on the forum. Kenny, SOS marine or Gavin at The Maintenance Shop. I changed mine at home in about a 1/2 an hour a couple of years ago. Any ofthese threeguys can get you back up and running in no time.

Mark


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## AUradar (Oct 1, 2007)

boat parts are usually tripple, but a thermostat for a vechile is so cheap you change them without thinking about it.


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## sosmarine (Sep 28, 2007)

If something did get stuck it the thermostat, the only way to clean it out is disassembly of the thermostat housing. Once you take it apart it would be foolish to not put a new in. Figure an hour labor plus therm and gasket, $150 might be a little high, but I don't know what their labor rate is.


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## Tuna Man (Oct 2, 2007)

$150.00 to replace a thermostat in a 350cu" isn't a litte high, I'd call that EXTREMELY high. Anyone worth their salt should be able to replace a $12.00 thermostat in LESS then 30 minutes. Looking at a minimum of a hour labor ($60-$75.00 shop prices)...the cost should be no more then $87.00. If I was to charge one to replace the thermostat I'd charge no more then $50.00 plus parts. For $150.00 I'd drive from Calera,AL to Pensacola,FL (250 miles) toreplace the thermostat in a 350cu"...Call me..I need a expense paid (diesel) trip to wet a line.oke

$150.00....Someone is OOTFM..Out Of Their F***ing Mind:banghead:banghead


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## Tuna Man (Oct 2, 2007)

Top front of engine. Hoses will go from thermostat housing to the exhaust headers. Thermostat in the housing. Need a screwdriver (clamp removal) and a 1/2" wrench/socket for removal of TWO bolts. May need to tap housing with a hammer due to housing stuck by the gasket.

Pictures of thermostat housings are listed on this site..Hope this helps.....

http://bpi.ebasicpower.com/c/MER8B/Thermostat+Housings+&+Covers+for+Mercruiser


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## sosmarine (Sep 28, 2007)

Flat rate is one hour according to Mercruiser. That would include removing the housing, cleaning all four surfaces, and installing new parts. Thermostat kit, which includes all gaskets, $29.


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## nic247nite (Oct 10, 2007)

We have the kits in stock and if you have questions on installation we can help.

Nick

one of the crew at Posner Marine


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## danthemanx07 (Oct 7, 2007)

If you have a raw water system like on my 5.7 Merc, pieces of the impeller would never make it to the thermostat; they get stopped in what I remember almost like a strainer toward the back of the engine. That may be different in the closed cooling systems. Sounds more like just a bad thermostat.


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## Tuna Man (Oct 2, 2007)

> *danthemanx07 (4/11/2008)*If you have a raw water system like on my 5.7 Merc, pieces of the impeller would never make it to the thermostat; they get stopped in what I remember almost like a strainer toward the back of the engine. That may be different in the closed cooling systems. Sounds more like just a bad thermostat.


Clue me in as to where the strainer is. I've had my whole system apart. Now as far as a strainer, I've not seen one anywhere in the system or in the schematic in any book. :banghead:banghead:banghead

The water comes up the outdrive, through the transom, through the power stearing cooler (if one is needed), and directly to the engine driven water pump.


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## sosmarine (Sep 28, 2007)

I think the P/S cooler is what he is refering to as a strainer. Could be wrong.


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## BlackFlag (Oct 23, 2007)

are you sure the strainer your talking about isn't the one preceeding the thruhull, before it reachs the impeller on your raw water pump. I've never heard of a thermo sticking cuz of a chewed up impeller but i don't work on gas burners that often.


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## Tuna Man (Oct 2, 2007)

> *sosmarine (4/12/2008)*I think the P/S cooler is what he is refering to as a strainer. Could be wrong.


If so it won't strain anything. Straight thru shot.


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## Tuna Man (Oct 2, 2007)

> *BlackFlag (4/12/2008)*are you sure the strainer your talking about isn't the one preceeding the thruhull, before it reachs the impeller on your raw water pump. I've never heard of a thermo sticking cuz of a chewed up impeller but i don't work on gas burners that often.


Not positive but nearly sure that what you are talking about is a enclosed system where the thru hullintake sucks inwater to cool the exhaust manifolds/risers. The engine cools using a coolant like that of a automobile.A I/O open (raw water) system cools the engine and exhaust from water brought in from the I/O foot (water pump), and to the engine driven water pump for circulating and out the exhaust thru the prop.


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## metal11 (Oct 7, 2007)

I don't think the p/s cooler on a merc is a straight through shot. It has fins inside of it that will catch an impeller blade and prevent the correct amount of water from flowing. It is normally on the port side below the exaust manifold. Just take off the hose and feel inside for the blade.


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## Tuna Man (Oct 2, 2007)

> *metal11 (4/12/2008)*I don't think the p/s cooler on a merc is a straight through shot. It has fins inside of it that will catch an impeller blade and prevent the correct amount of water from flowing. It is normally on the port side below the exaust manifold. Just take off the hose and feel inside for the blade.


That is where it is on mine. Not sure about the fins tho. But incorrect wording "*prevent* the correct amount of water from flowing". If anything it would maintain correct water flow. Water pressure in a open I/O system is about 5 to 7psi. If there are in fact fins in the cooler, in order to serve as a strainer (protection from impeller pieces)I think they would have to be so close as to inhibit water flow. The most critical point in the cooling system as far as impeller impedement would be in the tube from the foot water pump to the transom fitting.


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## metal11 (Oct 7, 2007)

It is not meant to be a strainer. It is meant to perform cooling. It just has fins like a radiator has. The impeller blades are to big to pass through and get caught. That is why it prevents proper water flow. No big deal just hang upside down and remove the hose clamp and then clear the cooler.


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