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160 to 140 Thermostat

cobia_265

New member
"I have a 2003 mercruiser 5.7

"I have a 2003 mercruiser 5.7 with a 160 thermostat that is raw water cooled. I seem to be running on the warm side (175 at idle, 185ish on plane). I just installed a 140 thermostat and I am now running 150 at idle and 165ish on plane. Does anyone know of an inherent problems using a lower rated thermy for this engine?"
 
If your engine is a Multi port

If your engine is a Multi port injection you should go to the original t-stat spec. The computer is calibrated for this temp. It is used to better atomize fuel and to lower exhaust emissions.
 
"Actually, you should use what

"Actually, you should use what Mercruiser recommends for that raw water cooled motor. I'm surprised that a 160 t-stat was installed in a RWC engine. What you have now is more common.

Jeff"
 
Sounds like the calibration of

Sounds like the calibration of the guage is off or the sending unit is malfunctioning.
 
"Gene- If this problem hasn&#3

"Gene- If this problem hasn't occurred since the beginning, you should find the actual nature of the problem. How long since the impeller was changed, have you been in water that had a lot of loose sand or did you drag the drive through silt? Even if it was in neutral, the motor running would cause a lot of sand or silt to be drawn into the motor and when it settled, it hardened enough that when the water came through later, it didn't dislodge whatever is in the motor.

You didn't give enough info for anyone to make any kind of informed diagnosis. The best thing you can do is make a list of any problems, quirks or events that may have caused this. List all of the service that has been done on it since you got the boat. If there hasn't been much done to it in the past, start with doing all of the scheduled maintenance. If it overheated, there's a reason for that and it should be addressed. If it froze, that needs to be dealt with, too. If it was run out of the water with no water to cool it, if it was more than about 15 seconds, your impeller may be toast. Don't just replace parts with different values just because it's running hot without looking for the cause.

FastJeff- as an example, Indmar doesn't use anything lower than 160° on their motors and a lot of them are in Mastercraft, Malubu and Supra/Moomba tournament ski boats. We both know that running at higher temperature makes the motor burn the fuel more efficiently. With the new emission standards, I don't know how a motor with a 140° thermostat would meet them. "
 
"This is not a MPI engine. I&

"This is not a MPI engine. I'm a second owner and have only had the boat since the beginning of the summer. In neutral, the temp always read 175 and climbed slightly higher on plane. Two weeks ago I overheated in my slip. The system was backflushed and a new impeller kit was installed. The temp read 175 at idle and climbed to about 187 on plane. My port manifold read 200 and my starboard was slightly lower. While I may sacrifice some economy, I figured I wouldn't sacrifice my engine."
 
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