To Thermostat or no to stat

[NeptuneMadness]

Hey friends, I have a 66″ 6hp Evinrude. I just got done rebuilding it. It needed some love. I went to fire it up with a thermostat, which I have never done, I was was unaware it took one! I ran it and it was running HOT! and this is a fresh start after a rebuild! So I was freaking out! I took the stat out, and runs perfectly smooth! Is there really an issue of not running with a thermostat? Yeah its running cool, and not it’s optimal heat. but I rather have it run cooler than Nuclear meltdown! Especially after a fresh rebuild.

[frankr]

What constitutes a total rebuild in your book? You may not be aware that that motor has two coolant paths through the powerhead. One path is thermostat controlled, and the other path flows all the time. The point is, perhaps one path is blocked (???).

[Mumbles]

The thermostat is there for a reason so you want to make sure it is installed and functioning correctly. A new one with its grommet and water pump servicing should be included in the rebuild.

The yellow arrows in this photo show the entry and exit holes for water so the thermostat will know how hot the motor is running. The arrow on the left shows a restriction and passage way which tend to plug easily. If this circuit is plugged, the motor will run fine but the thermostat won’t know what temperature the motor is at and it will never open when the motor gets hot. The blue arrow shows where the cooling water enters the head after leaving the exhaust cover.

After the water enters the head, it travels over top of the thermostat covers gasket before circulating thru the rest of the head and the block before being discharged overboard. This is the circuit Frank was referring to and it must be clear all the time or the motor will overheat. Since your motor runs hot with the stat in and normal with it removed, I’m betting there is blockage somewhere in this circuit and on the six horse motors, it usually happens in the passage way between the T-stats cover and the gasket. This is common in motors used in salt water or from too much sealer being applied to the gasket.

[NeptuneMadness]

A rebuild* New Piston heads, Rings, Honed, all new gaskets, Every water, and oil passage cleaned thoroughly. Its a good possibility their might stiil be a blockage.. I don’t know, maybe the Thermostat gasket is blocking flow, I’m scared to put it back in and have it over heat. I put way to much work into it.

[NeptuneMadness]

when the motor is cold, water won’t come out of the exhaust right? Then when it starts getting hot the water will come out the exhaust? When I had the Stat in, no water was coming out, I take it out, the water flows.

[NeptuneMadness]

Besides running cool, what would be the effects of the motor running cool, without a stat? Thank you very much for your time!

[frankr]

NeptuneMadness wrote:

when the motor is cold, water won’t come out of the exhaust right? Then when it starts getting hot the water will come out the exhaust? When I had the Stat in, no water was coming out, I take it out, the water flows.

No! As we pointed out, water will always flow through one path and be discharged, regardless of thermostat state.

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NeptuneMadness

[NeptuneMadness]

So good possibility I have a blockage, I had the stat in, and water was NOT flowing out, I took it out, and it the water was flowing out the back then.

[NeptuneMadness]

Can I pull the stat cover off, run the motor to see if water is flowing from the ports? or would water just gush out?

[frankr]

NeptuneMadness wrote:

Can I pull the stat cover off, run the motor to see if water is flowing from the ports? or would water just gush out?

You can, but there will be a lot of water gushing as you suggest. But look closely, and you will see water coming up through the hole that aligns with the gasket hole, AND also a smaller hole down in the side of the thermostat chamber (the upper yellow arrow in mumbles great picture)..

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NeptuneMadness

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