why have a thermostat

[Lostfisher]

What is the purpose of having a thermostat in an outboard. Wouldn't it be better just to have the motor run without one that way the engine would be cooled from the start. Also the boat operator doesn't have to worry about whether or not it is spitting water.

 

[bktheking]

Re: why have a thermostat

Cause 2 stroke motors require a certain temp to run efficiently, around 140F to be exact. The thermostat stops water flow to aid in the speed at which the motor heats up. Once the motor reaches operating temperature the stat opens and allows water to flow throughout the system. The stat will close and open in order to regulate proper temp. Same applies for a automobile motor, take out that stat and watch the fuel mileage go through the roof, coolant temp sensors go out of wack causing a rich mixture and heaters stop working. Run with the stat in it.

 

[robert graham]

Re: why have a thermostat

Outboards are designed to operate in the 135F. to 190F. temperature range, give or take a few degrees, but not too hot or too cool, and that's what the thermostat does. It's very important. Good Luck!

 

[bktheking]

Re: why have a thermostat

190 will set alarms off, at least that's what the sensors are rated at for the most part.

 

[bkwapisz]

Re: why have a thermostat

Thermostats also slow the flow of the water so that it can more effectively exchange the heat. If it runs too fast through the engine then the water passes through the center of the flow and not at the edges and the cooling efficiency is reduced.

This is in addition to what the other posters said. Just my worhtless contribution.

 

[R.Johnson]

Re: why have a thermostat

Aluminum piston, cast iron sleeve, or cylinder, water cooled aluminum block. They have to stay in harmony, size wise, or thing's start to get very tight.

 

[a70eliminator]

Re: why have a thermostat

Thermostats also slow the flow of the water so that it can more effectively exchange the heat. If it runs too fast through the engine then the water passes through the center of the flow and not at the edges and the cooling efficiency is reduced.

This is in addition to what the other posters said. Just my worhtless contribution.

I was thinking the same thing only along the lines of thermal shock, the water is regulated to maintain a constant temp by just letting a little water out at a time thus letting just a little more water in, without it you would have relatively cold lake water hitting hot cylinder walls.

 

[hawkman222]

Re: why have a thermostat

Also a motor will tend to accumulate deposits around the ports and rings when they run cool. I believe they call it 'Coking".

 

[bkwapisz]

Re: why have a thermostat

I was thinking the same thing only along the lines of thermal shock, the water is regulated to maintain a constant temp by just letting a little water out at a time thus letting just a little more water in, without it you would have relatively cold lake water hitting hot cylinder walls.

Could be. I just remember an automotive engineer telling me that running without a thermostat not only inhibits the engine from maintaining a proper operating temperature but also reduces the cooling effiiciency by not allowing the coolant so absorb enough heat from the motor dur to the speed it runs through it. Your "cold water on hot cylinders" make sense to me too.

It's all engineering mumbo jumbo that I don't pretend to understand-- I just know that it's there for a reason.

 

[Faztbullet]

Re: why have a thermostat

On a OMC crossflow the t-stats control the engine temp to do as everything posted, but most persons dont know that the t-stats are bypassed at 3000 and above rpm as the relief valves open to reduce water pressure in block. The t-sats cool and slightly close only allowing water to exit reliefs and stats,restriction is what hold temp in spec at high rpms.

 

[bktheking]

Re: why have a thermostat

On a OMC crossflow the t-stats control the engine temp to do as everything posted, but most persons dont know that the t-stats are bypassed at 3000 and above rpm as the relief valves open to reduce water pressure in block. The t-sats cool and slightly close only allowing water to exit reliefs and stats,restriction is what hold temp in spec at high rpms.

Thanks Fazt, I knew they had relief valves but I thought they were used to prevent damage if the stats stuck closed, didn't realize that it was to do with RPM, very cool!

 

[SKEETR]

Re: why have a thermostat

Shoot why have one in a car for that matter. I agree with the rest it's all about operating temps.

 

[bktheking]

Re: why have a thermostat

The rad cap acts as a pressure relief in the case of the automobile.

 

[a70eliminator]

Re: why have a thermostat

Could be. I just remember an automotive engineer telling me that running without a thermostat not only inhibits the engine from maintaining a proper operating temperature but also reduces the cooling effiiciency by not allowing the coolant so absorb enough heat from the motor dur to the speed it runs through it. Your "cold water on hot cylinders" make sense to me too.

It's all engineering mumbo jumbo that I don't pretend to understand-- I just know that it's there for a reason.

An auto cooling system is a closed loop, and yes the water has to hang in the radiator long enough to give up the heat or be cooled, removing the t-stat causes a continuous flow through the rad. not design.
Your outboard is raw water cooled open loop to the lake, the stat keeps operating temp design, you don't want hot cold hot cold, you want 140 degrees.

 

[a70eliminator]

Re: why have a thermostat

The rad cap acts as a pressure relief in the case of the automobile.

Also raises the boiling point @ 15psi water will go well over 212 degrees before boiling.

 

[Elbo]

Re: why have a thermostat

Well, what makes a t stat open or close?

 

[a70eliminator]

Re: why have a thermostat

Ummm, I'll let someone else answer that one, soon this discussion will get out of hand. Basically temp. dictates.

 

[coolguy147]

Re: why have a thermostat

also the t stat at high rpms keeps pressure in the system to pump water effiecntly then if you put your thumb over a hose and if you dont it doesnt go very far

 

[bktheking]

Re: why have a thermostat

Well, what makes a t stat open or close?

The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at perhaps 180 degrees F (different thermostats open at different temperatures, but 180 F/82 C is a common temperature). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly and pushes the rod out of the cylinder, opening the valve.

Ah the joys of cut and paste.

 

[bktheking]

Re: why have a thermostat

Also raises the boiling point @ 15psi water will go well over 212 degrees before boiling.

Totally agree.