what is the correct thermostat

F

fstalfire

New Member
Apr 26, 2015
25
chesapeake
Boat Info
1996 Sundancer 250
Engines
7.4
my 1989 300 sundancer didnt have a thermostat in it and i want to instal one...it has a mercruiser 5.7 and i ordered a 54mm 140 degree but the diamiter it to big......there are 3-4 different kinds listed for 5.7 motors but which is the correct one?
 
if you have the serial number of your motor, you can look up the part number on Mercruiserparts.com
 
I will be down at the boat tomorrow and will look and post then if you can wait.
 
There is a differet temp for FWC, and RWC too.
 
fstalfire said:
my 1989 300 sundancer didnt have a thermostat in it and i want to instal one...it has a mercruiser 5.7 and i ordered a 54mm 140 degree but the diamiter it to big......there are 3-4 different kinds listed for 5.7 motors but which is the correct one?
Click to expand...
I told my Merc dealer that 140 is too cold for any engine to run at and put 160's in both of my 7.4's. My warranty expired a long time ago and close to 50 years of internal combustion experience tells me that 160 is better than 140 for big block engines.
Just my opinion, I know Merc says 140 is correct.
 
I've been looking at all the websites like ebasic and wholesale marine and everything is 54mm which is to big for my housing.....not sure what I'm missing, shouldn't be this much a pain to find a thermostat
 
I think I was looking at it wrong, i was thinking the thermo went into the brass sleeve (it didn't have a thermo when i got it so i didn't have a point of reference)
so does the thermo go on the intake and the housing goes over it or does it go under the brass sleeve??
 
Raw water is 145 fresh water cooled is 165.
Click to expand...

Huh ? its either saltwater or freshwater, I NEVER heard it be put that way before. :wow:
 
You need to go to one of the parts web sites and find your thermostat housing then you will know which stat you need. My 88 5.7 original stat was cylinder shaped that fit down into a brass sleeve the new one looks like a regular stat. The first picture for a 1989 5.7 bellow new style stat is a 807252-1 (140 degree)
the second picture also takes a 807252-1



 
I have the one in the first pic.....it must go under the brass sleeve...the diameter of the thermo is the same as the brass sleeve so it can't go in side the brass sleeve
 
Summer Fun II said:
Huh ? its either saltwater or freshwater, I NEVER heard it be put that way before. :wow:
Click to expand...

Refers to the cooling system rather than the actual water involved. Raw water -- outside water (lake or ocean) runs straight through engine cooling system. "Fresh water cooling" -- outside water is run through a heat exchanger then out the exhaust; water or coolant is what runs through the engine and heat exchanger. Same principle as your car except the "radiator" that uses air to cool the coolant is replaced by a heat exchanger that does the same job using ambient water. The advantage if you're a saltwater boater is that you're not running salt water through your nice engine block, which therefore lasts quite a bit longer.
 
I guess the internet is kind of complicated to find out information so here is another picture to remove your doubt you can see how to install the new style thermostat. So to head off another question when you do install it do not put any type of gasket compound on the gasket that has the little brass buttons on it or the temp.sensors will not work properly.

 
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