engine temp?

[magster65]

Does anyone know what the ideal running temperature is for a 7.4 merc.? Mine warms up fairly fast but it only gets to 130-135. I have 2 temerature guages so I'm pretty sure the reading is accurate.

 

[Bondo]

Re: engine temp?

Rule of thumb is;<br />140* for Raw water cooling......<br />180* for Fresh water cooling......

 

[Blue Thunder]

Re: engine temp?

That is interesting bondo, never heard that before. Makes sense to me. I run closed cooling and my engines run 150-155*. Do you think this should be higher? I run a 143* thermostat. I generally focus most of my concern on oil temps being around 220*-230*.<br /><br />BT

 

[flashback]

Re: engine temp?

Magster, there are several posts on engine temp on the forum and from what i can tell, most folks will agree that if you are running a raw water unit in fresh water you can run around 180, but if in salt, you need to keep it around 140 as higher temps can cause the salt to disolve and form deposits in the system. personally I have never run in salt enough to say first hand. on the closed circuit system, I would imagine 180 as bondo said would be good..............

 

[magster65]

Re: engine temp?

More info... it's a fresh water cooled system including the exhaust manifolds and it's moored permanently in the saltchuck. I read somewhere that the peak thermal efficiency of a gas engine is up around 195... why are boats set up to run cooler? So mine should be running around 180? <br /><br />It must have the wrong or a sticky thermosthat in it.

 

[Bondo]

Re: engine temp?

Ya, Raw water cooled, run the 140* T-stat... It's the salt that's Desolved in seawater, that crystalizes in the porous cast iron, that causes the problems... you'll NEVER Flush it out at the higher temps.... My boat is raw water cooled, I boat in fresh water 99% of my time, But I Still run the 140* T-stat.....<br />Yes, Thermal effeicency is at about 195*, I'd Switch to the 180* T-stat IF you're running Freshwater(closed system) cooling.....<br />Merc.'s New EFI motors with the closed cooling system, run higher temps....So the 'puter doesn't richen the mixture too much....

 

[magster65]

Re: engine temp?

Yeah, it's FWC with enclosed manifolds. The only thing cast iron the raw water touches is the risers on the way out. Thanks for the info.<br />