1990 omc 5.7 thermostat

macorre4

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hi can any one tell me what degree thermostat i need for this motor because i have 2 different manuals for this motor and one says that the standard is 140 and the other says 160 but i put a 160 on my motor and the gauge says 3/4 hot and ive changed everything on it water pump raw water pump temp sensor gauge head gaskets and had the heads redone
 

bruceb58

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Re: 1990 omc 5.7 thermostat

What manuals are you referring to? Factory manual or Seloc or Clymer? Factory specifies 160.

Also, Don't trust the gauge. Get an IR thermometer and measure the temp where the temp sender is.
 

macorre4

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Re: 1990 omc 5.7 thermostat

well the omc cobra factory manual says standard thermostat is 140 degrees but seloc manual says 160 i thought it was the guage but replaced it with a new one today same thing the gauge has no numbers its only color coded i put water at 150 degrees with the temp sensor in it and the gauge was almost in the middle wht do u think i think i should go with the factory manual
 

bruceb58

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Re: 1990 omc 5.7 thermostat

Could be the sending unit as well. That is why you need to use an IR gun to really determine what the temp is.
 

macorre4

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Re: 1990 omc 5.7 thermostat

i changed everything the sending unit impellor waterpump everything is new
 

bruceb58

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Re: 1990 omc 5.7 thermostat

Now you need to measure with IR gun.

What condition are the manifolds? Have you pulled off a hose from the drive to the thermostat housing to see what the water flow was like? Boat used in salt water ever?
 

macorre4

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Re: 1990 omc 5.7 thermostat

yes i have its got good water flow plus the manifolds are new the motor is not overheating it gets to 3/4 and it stays there i accelerate the motor for a while and it stays at that temp it doesnt move i believe its the thermostat so im going to try a 140 according to the omc cobra factory manual
 

Reinell-BRXL-191

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Re: 1990 omc 5.7 thermostat

3/4 on the gauge, should be just about right with a 160 stat... I think that 140 is too low, and will cause loss in fuel efficiency.. My gauge shows right about 175 at 3/4 - so a tad warm, but well within operating temperature..
 

bruceb58

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Re: 1990 omc 5.7 thermostat

yes i have its got good water flow plus the manifolds are new the motor is not overheating it gets to 3/4 and it stays there i accelerate the motor for a while and it stays at that temp it doesnt move i believe its the thermostat so im going to try a 140 according to the omc cobra factory manual
You could be wasting your time and money throwing parts at it. Measure with an IR gauge to be sure you even have a problem.
 

Don S

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Re: 1990 omc 5.7 thermostat

This thread is almost a year old :facepalm:
 

bruceb58

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Re: 1990 omc 5.7 thermostat

Got sucked in by Reinell. I am usually good at looking for this.
 

Reinell-BRXL-191

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Re: 1990 omc 5.7 thermostat

Got sucked in by Reinell. I am usually good at looking for this.

Oh sure.. blame it on me.. like I went looking for a year old post to dig up... I pinky swear, it was in the top of the list, so I replied... I would say it can be closed..
 

Lou C

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Re: 1990 omc 5.7 thermostat

I have never seen a 140 listed for any of the Cobras, only 160s, but for other's information, with a 160 your temps will vary from about 160 to 175, should not be more than that. Mine will hit 175 just after coming off plane, usually its between 165-172, on the gauge, and if I shoot the manifold right under the thermo housing it reads a bit lower, like 155/160...
 
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