What degree thermostat for 5.7 mercruiser?

[oldseaox]

I have a I/O Alpha with a 5.7 Jasper replacement engine, raw water cooled. The boat is used exclusively in salt water in Florida. I have been advised to change the thermostat because the boat came from fresh water in NC. The problem is deciding what degree thermostat to use for salt water. I have been told 140* and also 160*.

 

[Scott Danforth]

Re: What degree thermostat for 5.7 mercruiser?

I always ran a 160. 140 is barely warm enough.

 

[tpenfield]

Re: What degree thermostat for 5.7 mercruiser?

If it ain't broke . . . Is there anything in particular about the advice on replacing the thermostat?

160 would be the way to go.

Also, if the boat/engine is coming from strictly fresh water use, and now going into salt water use, it is a great opportunity to go with a closed cooling system. A 'full' closed cooling system will save you $,$$$ on manifold replacements and keep the engine cooling passages in a much more pristine condition.

 

[oldseaox]

Re: What degree thermostat for 5.7 mercruiser?

The only issue observed is when rpm exceeds 4200 the temp slowly creeps up until the warning goes off and the gage indicates 185*. lowering the rpm to 3800 causes the indicated temp to rapidly drop to 170* which appears to be "normal". I am considering getting a infrared heat checker to look for hotspots, thoughts?

 

[tpenfield]

Re: What degree thermostat for 5.7 mercruiser?

OK, understand.

A new thermostat will probably not fix that situation, but it may be worth a try. Usually the alarm should go off at about 200 degrees. at 185 degrees the 160 thermostat should be fully open. So, unless the problem is the thermostat, the 140 will probably give you the same results.

 

[crazy charlie]

Re: What degree thermostat for 5.7 mercruiser?

I dont believe I have seen any listing for that engine RWC over 143.As a matter of fact since the last 3 boats I have owned all have that motor and i have only run in salt water,I am sure of it.Salt water turns to pure salt at 190 and cloggs.Charles

 

[Scott Danforth]

Re: What degree thermostat for 5.7 mercruiser?

I love it when people quote things without knowing the truth

 

[Fun Times]

Re: What degree thermostat for 5.7 mercruiser?

For what stock temperature to run depends on what year, engine model or design cooling system you have.

Three examples can be found below.

STANDARD COOLING SYSTEM(DESIGN I)
STANDARD COOLING SYSTEM(DESIGN II)
STANDARD COOLING SYSTEM(DESIGN III - ALPHA)
http://www.mercruiserparts.com/selectDocs.asp?doc_nbr=816596

 

[Volphin]

Re: What degree thermostat for 5.7 mercruiser?

I love it when people quote things without knowing the truth

OMG! That was the funniest post EVER! I concur my friend. Now send me $50 for a new keyboard as I spit coffee all over this one...