Normal temperature for a 5.7 Merc?

[brad614]

I just got a 1986 Sea Ray 25 FC with a 5.7 Mercruiser I/O. Took it out for the first time today and the temperature ran about 170-175. Is that normal? The guage only goes to 220...The engine is supposed to be fairly new.

 

[dave4881]

Re: Normal temperature for a 5.7 Merc?

I just got a 1986 Sea Ray 25 FC with a 5.7 Mercruiser I/O. Took it out for the first time today and the temperature ran about 170-175. Is that normal? The guage only goes to 220...The engine is supposed to be fairly new.

That's about what mine runs at. I have an '87 Seaswirl Spyder with Cobra 5.7L I/O. Thermostat on motor is what regulates water temp. Sounds like yours is fine.

 

[brad614]

Re: Normal temperature for a 5.7 Merc?

I am not sure how to tell if it has good water flow - how would I test that?

I will try feeling the manifolds the next time I have it out. They should be warm but I should still be able to keep my hand on them, correct?

I really don't know how to check it with an alternative thermometer short of running a whole new guage...

No idea about the thermostat.

 

[Gary H NC]

Re: Normal temperature for a 5.7 Merc?

First thing to do when buying a used boat is to replace the water pump impeller.170 to 175 is about normal but i would replace the impeller anyway.
It should be done about every other season.

You can buy a cheap infared thermometer at most any auto parts stores.
Just aim it at the thermostat housing and see what readings you get.
They are a handy tool for boat engines.

 

[sethjon]

Re: Normal temperature for a 5.7 Merc?

First thing to do when buying a used boat is to replace the water pump impeller.170 to 175 is about normal but i would replace the impeller anyway.
It should be done about every other season.

You can buy a cheap infared thermometer at most any auto parts stores.
Just aim it at the thermostat housing and see what readings you get.
They are a handy tool for boat engines.

170-175 is not normal. If the gauge is correct then its not that hot, but if it goes abother 10-15 degrees up which would not be abig deal its way too hot. With a 160 t stat it should be 160.

 

[brad614]

Re: Normal temperature for a 5.7 Merc?

OK - so I took it out this weekend and tried a number of the things mentioned above. The T-stat housing only registered about 112 on the infared thermometer, as did the port heat riser. The Starboard riser read 123. All of this is while the dash guage showed 170 - 175. Think I should temporarily install a cheap mechanical guage from the auto parts store to see if maybe the dash guage or sending unit is the culprit? Note that once the temperature reached that level, it didn't fluctuate at all either at an idle or high RPM's.