71 125 Johnson thermostat

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jwinters

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Joined
Oct 6, 2010
Messages
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we decided to start the boat a while back, it hadnt been run in 10 or 12 years. We put a new waterpunp in and started it, but wasnt getting water. We then removed the thermostat housing, and they were all coroded up. We left them out and put it back together just to eliminate that problem before buying anything. Now one head runs cool and the other one gets hot quick. We have had the bottom end back down and checked the key and to make sure the tubes were lined. Hope somone can help Thankss
 
E

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 71 125 Johnson thermostat

You should put a new thermostat back in, then try running the engine. The thermostats act like a restrictor, holding water in the powerhead till the block fills completely with water. This promotes even cooling at idle. With no stat, the water easily flows out of the block, perhaps before the block fills to the top with cooling water. If it still overheats, you may want to pull the heads and check the positioning/condition of the 4 rubber water diverters next to each cylinder. You can also pull the 2 large hoses going into the thermostat housing to check for water flow. Each hose discharges water from one head. Check for similar flow rates.
 
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