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3.0 Mercruiser Possible Over Heating

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onegoodoleboy

New member
I am fairly new to the boating world, but I am mechanically inclined. I just recently had a broken starter bolt problem and had to pull the motor out of my pontoon to fix it. I marked and took several pictures of how it all went back together. Everything went back together fine, and it started up and ran fine, but after approximately 10 minutes at 1000 rpm the temperature gage climbed to 180 plus degrees. I am trying to find the root cause. I am sure it is something that I did wrong, but dont know what.

Below are some facts:

1) I am utilizing a barrel full of water with the lower unit lowered well below the pump inlets.
2) I have replaced the temperature sending unit, no change.
3) I have replaced the thermostat with a factory replacement (160 degrees).
4) I replaced the spark plugs MR43LTS with R44LTS.
5) I have tested my water temperature gauge, and it is good.
6) I have grounded out the tan wire going to the temperature sending unit and it pegs the temp gauge, therefore my wiring is good.
7) I also ran a wire directly from the gauge to the sending unit and it still went 180 degrees plus.
8) I have removed the thermostat and there is no issue with overheating.
9) I have removed the inlet hose to the thermostat housing, and started the motor and I have good water pressure there.
10) I have removed the exhaust hose to the thermostat and started the motor, water is coming out of the thermostat very good. there is also some water flowing out of the hose, is this correct?
11) I have good discharge water coming out of the transom plate on the port side, but only a spray coming out of the starboard side. The port side water coming out, maybe 20 - 30 degrees warmer than what it is taking in.

With all this being said, what do you guys reccomend that I do next?
 
Oh and I should add that I have shot the thermostat housing and several places on motor with an IR gun and I do not get anything over 160 degrees.
 
per the gauge it reached 200 degrees... I could touch the engine. The oil wasnt even warm in the oil pan.....

I am having a few tell me that its a blown head gasket.... I just cant understand why the gauge shows 200 degrees and I shoot the housing near the sending unit and I do not get anything that close.
 
1. what year is motor?

Most used 143 degree thermostat, unless closed cooling (heat exchanger in system).

Running a 143 will typically give ~ 150-160 all day long except under hard use in warm water it may reach 180.

running a 160 will typically give ~170 to 180 all day long and reach 190 + under hard use and warm water....

Did you replace the thermostat with the same temp rating?

running in a barrel is not a great idea, Way to much airration (bubbles)!!!!!!! also the water gets very warm if not being fed by a cold water supply.

Better to use ear muffs..........
 
1) Motor is 2004
2) Getting up to 200 degrees just idling at 1000 rpm's.
3) Thermostat was replaced with a 160 degree, same as old one.
4) Barrel is fed by city water continuously. I used muffs originally but was afraid that the water pressure was pushing water thru the motor, covering up a potential pump issue.
 
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