Evinrude cooling system query

[rajabatis]

Hi Folks, I am trying how to better understand how my engine cooling system works and wonder if someone can help. This engine is a 1992 50 horse power
When the engine is started water comes out of the tell tale driven through the engine by the rotating impellor. My questions are:
(1)Is the cooling system like a cars system?
(2) Does it have a thermostat that controls the temperature round the cylinders and the flow of cold water coming in?
(3)Does that thermostat cut off the cold water intake and bypass the cylinder cooling process and once the cylinder temperature becomes too high, allows the cold water to flow through again?
(5) If the above is correct what temperature approximately would the water temperature be to open the thermostat?
Or (5) have I got that totally wrong????
Thanks in advance.

 

[emdsapmgr]

Re: Evinrude cooling system query

You have a thermostat on the engine. It is located under a large plastic screw-in fitting at the top of the head. It will open at 143 degrees-which means it can run hotter that that at idle. You will get a constant hot warning horn somewhere over 210 degrees, which may silence at 175. The thermostat is spring loaded. When you get the engine up to speed, the increased water pressure through the pump will push the whole thermostat away from it's seat, causing massive water flow through the block. Possible that the temps will go down in the block when this happens. This is to insure ample cooling when running on plane. When running, you should always have water coming out of the telltale. For optimal combusion, economy and engine logevity you need to run with a thermosat.

 

[WillyBWright]

Re: Evinrude cooling system query

(1) Not really. It's completely open. It draws water from the lake (or whatever you're running in), cools the powerhead, then dumps it out into the exhaust.
(2) Yes.
(3) Sort of. But the thermostats only work at low pressure (low rpm). The thermostat doubles as a high pressure bypass valve. Once enough water pressure is produced, it forces the thermostat off it's seat. When pressure drops, a spring pushes the thermostat back into place.
(4) Depends on the thermostat, I think yours is a 143.
(5) Mostly right.

 

[rajabatis]

Re: Evinrude cooling system query

Hi Thanks for the reply. A bit puzzled though wouldn't opening at 143 make it run cooler? As this is bringing in cold water sooner. Would i not run hotter at tickover if the thermostat opened at a higher temperature nearer the 175 you mentioned?

You have a thermostat on the engine. It is located under a large plastic screw-in fitting at the top of the head. It will open at 143 degrees-which means it can run hotter that that at idle. You will get a constant hot warning horn somewhere over 210 degrees, which may silence at 175. The thermostat is spring loaded. When you get the engine up to speed, the increased water pressure through the pump will push the whole thermostat away from it's seat, causing massive water flow through the block. Possible that the temps will go down in the block when this happens. This is to insure ample cooling when running on plane. When running, you should always have water coming out of the telltale. For optimal combusion, economy and engine logevity you need to run with a thermosat.

 

[OBJ]

Re: Evinrude cooling system query

At rpms, likely between 1/2 trottle and WOT, your engine temp is likely running in the 150 > 155* range and depends on the total flow of water through the engine since the t-stat is probably staying wide open and off the seat. Remember it's an open system and as rpms increase so does water flow.

(Note: The throttle position vs. t-stat opening I'm using is relative to engine type, ie...# of cylinders, hp, etc., but serves as a good example of what's going on in the engine)

At rpms below 1/2 trottle, the t-stat will likely be opening and closing to maintain engine temp. at 143 > 145* range. Also keep in mind that heat builds up very quickly in engines. Even at idle, with a poor operating t-stat or pump, an engine can over heat in minutes.

 

[rajabatis]

Re: Evinrude cooling system query

Thanks that's very helpfull.

At rpms, likely between 1/2 trottle and WOT, your engine temp is likely running in the 150 > 155* range and depends on the total flow of water through the engine since the t-stat is probably staying wide open and off the seat. Remember it's an open system and as rpms increase so does water flow.

(Note: The throttle position vs. t-stat opening I'm using is relative to engine type, ie...# of cylinders, hp, etc., but serves as a good example of what's going on in the engine)

At rpms below 1/2 trottle, the t-stat will likely be opening and closing to maintain engine temp. at 143 > 145* range. Also keep in mind that heat builds up very quickly in engines. Even at idle, with a poor operating t-stat or pump, an engine can over heat in minutes.

 

[Silvertip]

Re: Evinrude cooling system query

The thermostat is also used at slow speeds to speed engine warm up, promote better idle quality, and to prevent cold seizing. Cold seizing can occur because the pistons heat up and expand quickly whereas the cylinder itself does not. Without a thermostat the piston-to-wall clearance can close up and therefore seize the engine.