Thermostat replacement

[russ]

Can anyone tell me how to replace the thermostat on my 2005 Mercruiser please? It over heated this weekend so I assume it could be the cause. There is no obstruction around the B3 leg and a new impeller was fitted a few weeks ago.
I believe its just removing the two bolts on the top of the engine. But can this be done whilst still in the water?

 

[dpb]

You don't say which model but most of the petrol mercs have the thermostat housed in a casing that is the highest bit at the front of the engine. It has at least two rubber hoses coming off it at each side.
Undo the two bolts at the top of the casing to remove the top and you will find the thermostat inside.
Easy to remove and check its operation in a pan of water on a stove.
No problem doing it with boat in the water as the casing is usually well above the external water level.

 

[piratos]

Can anyone tell me how to replace the thermostat on my 2005 Mercruiser please? It over heated this weekend so I assume it could be the cause. There is no obstruction around the B3 leg and a new impeller was fitted a few weeks ago.
I believe its just removing the two bolts on the top of the engine. But can this be done whilst still in the water?

Irrespective of which Mercruiser you have - have you checked that there is a free flow of Seawater ?? Usually overheating ist because of blocked exhaust.....

 

[russ]

Irrespective of which Mercruiser you have - have you checked that there is a free flow of Seawater ?? Usually overheating ist because of blocked exhaust.....

Whats the best way of checking for free flow?

Its a 5.7 Mercruiser.
I have changed thermostats on cars in my younger days so this will not be too much of an issue to do. I have 6 hoses coming from the top of the casing. 4 from the main body of the thermostat housing and 2 from a top mounted T-piece going to the risers.