How is a water Cooled Outboard Motor Cooled?

[fairdeal]

Yamaha thermostats (and most I believe) have a passageway so that a bit of water can get across the thermostat at all times.

That has been my lifelong observation as well.


although I have no other reference to support it:

I believe the main reason it is there, is to prevent the thermostat from being "airbound" - and if it passes a little water, that is a "side effect"



edit: from Stant.com

Many thermostats have a “jiggle pin” or “check valve” that allows trapped air in the cooling system to pass through the thermostat and be released from the system.

If a Stant thermostat does not have a jiggle pin, it will have a "bleed notch” or other method of removing air from the system.

[cpostis]

Yamaha thermostats (and most I believe) have a passageway so that a bit of water can get across the thermostat at all times.

This I know, but the reason for that "bit of water ", in my opinion, is to prevent stagnant cooling water from remaining around the thermostats, thus receiving a more accurate average temperature to open the thermostat appropriately.

I just now placed a t-stat on the end of a cut off garden hose (about 60psi) and observed a dribble of water through the "by-pass passages" within the t-stat. No way that amount could have any effect on cooling capability.

I looked at an automobile t-stat. they have a small passageway orifice with a loose piece of brass like a pin. I assume this is to prevent clogging of orifice?

Here is a pic of both:

[IMG]T-Stats by Charles Postis, on Flickr[/IMG]

What do you think?

[fairdeal]

I looked at an automobile t-stat. they have a small passageway orifice with a loose piece of brass like a pin.

I assume this is to prevent clogging of orifice.

Hillier's Fundamentals of Motor Vehicle Technology, Book 1
Victor Albert Walter Hillier, Peter Coombes
Nelson Thornes, 2004

[fairdeal]

I just now placed a t-stat on the end of a cut off garden hose (about 60psi)
and observed a dribble of water through the "by-pass passages" within the t-stat.
No way that amount could have any effect on cooling capability.

Chuck, you might be interested in the testing I did with my F225
which has a similar (but not identical) thermostat to yours.
( the F225 thermo has 3 "dimples")

With a garden hose connected to the engine flush port (60 psi static, 40 psi dynamic)

I measured the flow through the closed thermostat to be 200 mLs per minute

here's a video:

https://vid.me/IuR8

[pstephens46]

When you fellas get done with this water business, perhaps the next project could be a discussion of the electrical system on a typical outboard. How all these various coils and their various names relate to the operation of the motor. Of course, I could go look it up myself. Wonder if there is some sort of animation on Youtube (which Rodbolt hates)?

[boscoe99]

Stated reason for having the bleed hole is to allow air to pass so that water can flow to where it needs to be. No air flow, no water flow. Same as is seen in a water pressure gauge.

Now maybe, just maybe, any water flowing through the air bleed hole might, just might, help the thermostat to open just a tad sooner than it otherwise might open. That is, water flowing up, through and out the thermostat bleed hole might cause hotter water from down below to impinge upon the thermostat and cause the thermostat to open more quickly.

Water is not the best conductor of heat. If cold water were to be surrounding the thermostat it might not open when desired. A bleed passage in the thermostat would allow the cold water to pass on by so that warm and then hot water can flow. Helping the thermostat to open more quickly.

Methinks we are heading off a tangent of some sort. Waiting to see where we go from here.

[boscoe99]

When you fellas get done with this water business, perhaps the next project could be a discussion of the electrical system on a typical outboard. How all these various coils and their various names relate to the operation of the motor. Of course, I could go look it up myself. Wonder if there is some sort of animation on Youtube (which Rodbolt hates)?

Youtube is a pretty good source for animation.

I got stuff with words if you be interested. For example:

CDI THEORY OF OPERATION
In its simplest form, a CDI ignition is composed of the following elements:
Flywheel – The flywheel or rotor contains the magnets (two, three or six magnets) to generate a voltage in the charge coil and the pulsar coil. When the magnets move in front of a coil, a current is generated for the ignition. The flywheel is aligned with the crankshaft by a flywheel key for ignition timing purposes.
Charge Coil – The charge coil is a one wire or two wire coil, depending on engine size that is mounted on a timer base plate under the flywheel.
It produces an AC voltage that is delivered to the CDI box. Most 2-stroke engines (75hp and larger) use a combination of low speed and high speed charge coils.
Pulser Coil – The pulser coil is a one or two wire coil (depending on the ignition system) that delivers an AC voltage signal to the CDI box for triggering the ignition timing. The pulser coils are mounted on a timer base and are located either under the flywheel or outside the flywheel.
CDI Box – The CDI box receives inputs from the charge coil, converts the signal to DC current and stores it in a capacitor. When the pulser coil signal
is received by the SCR in the CDI box, the stored voltage is discharged to the primary of the ignition coil. The primary components of the CDI box are diodes to convert the AC voltages to a DC voltage, a capacitor to store the rectified charge coil voltage, and an SCR (Silicon-Con*****ed Rectifier) that serves as an electronic switch. When activated, it delivers the stored voltage
from the capacitor to the primary of the ignition coil.

[cpostis]

Stated reason for having the bleed hole is to allow air to pass so that water can flow to where it needs to be. No air flow, no water flow. Same as is seen in a water pressure gauge.

Now maybe, just maybe, any water flowing through the air bleed hole might, just might, help the thermostat to open just a tad sooner than it otherwise might open. That is, water flowing up, through and out the thermostat bleed hole might cause hotter water from down below to impinge upon the thermostat and cause the thermostat to open more quickly.

Water is not the best conductor of heat. If cold water were to be surrounding the thermostat it might not open when desired. A bleed passage in the thermostat would allow the cold water to pass on by so that warm and then hot water can flow. Helping the thermostat to open more quickly.

Methinks we are heading off a tangent of some sort. Waiting to see where we go from here.

Don't mind "heading off a tangent".

I like to think of an outboard motor as being an "assembly" of various "sub-assemblies". Each of these "sub-assemblies" have its purpose. Within these "sub-assemblies" are "components" which have their purpose within the "sub-assemblies". Each of the "components" are designed to operate and perform their purpose within the "sub-assemblies".

Now, if all "components" are operating as designed, all sub-assemblies will operate as designed, and the outboard motor will operate as designed.

Therefore, understanding how each "component" operates, helps in diagnosing poor performance of the outboard motor "assembly".

Thanks guys!!!

[fairdeal]

Now maybe, just maybe, any water flowing through the air bleed hole might, just might, help the thermostat to open just a tad sooner than it otherwise might open. That is, water flowing up, through and out the thermostat bleed hole might cause hotter water from down below to impinge upon the thermostat and cause the thermostat to open more quickly.

A bleed passage in the thermostat would allow the cold water to pass on by so that warm and then hot water can flow. Helping the thermostat to open more quickly.

I have no doubt that there would be some effect as you describe;

what we don't know is to what extent that is taken into account by the engineers for any particular engine.

In a similar vein, in my brief Google re the jiggle pin,

I also learned that automobile engineers fistfight over whether the thermostat belongs on the inlet or outlet side of the circulating pump in a closed system.

But apparently they agree that the opening temperature will need to be substantially different - >20 F or so - depending on which side it goes on.

[boscoe99]

I have no doubt that there would be some effect as you describe;

what we don't know is to what extent that is taken into account by the engineers for any particular engine.

In a similar vein, in my brief Google re the jiggle pin,

I also learned that automobile engineers fistfight over whether the thermostat belongs on the inlet or outlet side of the circulating pump in a closed system.

But apparently they agree that the opening temperature will need to be substantially different - >20 F or so - depending on which side it goes on.

I retired from a manufacturing company that also did their own design. The fights you would not believe. I always pitied the chief engineer who had to be making the final calls on thousands of issues and who then had to deal with all of the hurt feelings from folks that did not get it there way. And that was back in the day when management did not necessarily care about anyone's feelings. Before the days of having safe spaces, soft cuddly toys, low music, aromatherapy, and other such nonsense. A boot in the ass was more likely than not given out to get folks back into line.

[cpostis]

Hillier's Fundamentals of Motor Vehicle Technology, Book 1
Victor Albert Walter Hillier, Peter Coombes
Nelson Thornes, 2004

"when the system is being filled"? So no air is entrapped around the t-stat? Once filled in a "re-circulating system" it is not needed unless the system is drained and re-filled?

In an outboard, where the system is a "once through system", it is necessary any time the motor is started after shut down and the system drains?

Just thoughts! I don't think this is valuable information for any type of diagnoses, just conversation.

[fairdeal]

Once filled in a "re-circulating system" it is not needed unless the system is drained and re-filled.

In an outboard, where the system is a "once through system", it is necessary any time the motor is started after shut down and the system drains.

That is my take on it as well.

[99yam40]

"when the system is being filled"? So no air is entrapped around the t-stat? Once filled in a "re-circulating system" it is not needed unless the system is drained and re-filled?

In an outboard, where the system is a "once through system", it is necessary any time the motor is started after shut down and the system drains?

Just thoughts! I don't think this is valuable information for any type of diagnoses, just conversation.

Just think about when people do not service the stats as they should and stuff builds up in that area, seems it could plug off that bleed causing air trapped where the water cannot come in contact with the stat .
how long would it take for the air to transfer the heat to the sensing bulb of stat or the metal of the stat in contact with the motor to transfer enough heat to the bulb to cause it to open even if it could due to build up on it

[panasonic]

"I wonder if the cooling water is sufficient to keep the temperature of the aluminum way below melt point."

Try this little experiment to see how good water conducts heat away. Take a empty Styrofoam cup and put a cigarette lighter to the bottom of it, it will burn through in a second....Now take another Styrofoam cup and put some water in it and do the same with the lighter, it wont burn through, just blackens the Styrofoam.

[Zara Spook]

This is what I found at the end of this season. Despite regularly flushing with fresh water, all four thermostats (twin 115hp V4 2-strokes) were badly salted-up.

For folks who have taken a look inside engines like this -- do you find any difference in salt accumulation if the flushing has been done with a salt remover such as Salt-Away?