1978 mercruiser 228 thermostat location

[Hondaguy1]

So I have a 1978 Mark Twain with a 228 mercruiser inboard. Last year I went to replace thermostat and lower water pump. Tore apart thermostat housing and got side tracked for a cpl weeks and when I went to put it back I couldn’t remember which side of housing the t stat went. I put it under top cover and now it won’t get up to temp. Is it supposed to go right on top of intake manifold? It has a spot in 2 places like it looks it could go. Just don’t wanna burn it up somehow. Thank you

 

[Fun Times]

The thermostat goes up top/inside the thermostat housing...But sits down inside the housing too...Did you put in a new Cork or O-ring type gasket under the thermostat?

https://www.mercruiserparts.com/bam/subassembly/31550/1593/8
http://boatinfo.no/lib/mercruiser/manuals/mercruiser3.html#/862
http://boatinfo.no/lib/mercruiser/manuals/mercruiser3.html#/888

 

[Hondaguy1]

No I didn’t put any gasket under the thermostat. I put new gasket between thermostat housing and intake and then a new gasket with the thermostat under the top cover. But what I don’t understand is how the thermostat does anything under top cover. Seems to me it should be under the thermostat housing and it even has a grove on intake like it could go there. But I see the pic shows it above the housing. I’m just a car mechanic and new to boats. Thanks

 

[GA_Boater]

HG1 - I think that what's throwing you is the difference between car or truck and marine use.

A car has one hose from the radiator and the thermostat is in the intake to allow radiator coolant in when it opens.

In a boat motor the thermostat is in the housing mounted on the intake because more than just the block is cooled with all the extra hoses on the housing.

The groove in the intake is because the same intake manifold is used for car/truck and marine. The marine housing raises the thermostat from the intake to the thermostat manifold to cool the extra marine parts.

Make sense?

 

[Hondaguy1]

Okay yeah that makes sense. Just wanted to make sure. Thank you. Is it common for them not to get up to operating temp while on the muffs?

 

[Fun Times]

Is it common for them not to get up to operating temp while on the muffs?

If it's missing or has a compromised gasket under the thermostat it could be why it's not reaching full temp for a long while.