I've been thinking of the recent exhaust stack problems for someone's F225 that has been numerously posted. Last year I had my first overheat alarm on my SX150. I considered what I did , and the drastic improvement in performance.
So, I thought I'd put together what I thought about how an outboard cooling system works. I also thought of how valuable an infrared thermo gun is worth in determining the performance of a cooling system.
I know different Yammies are "piped and sensored" differently, but would appreciate some input to what I have put together so far.
This page one of a draft. If some of you want to comment by placing your comments in red via quoting this, I would appreciate it.
What is an outboard motor cooling system?
An outboard water cooling system is a once through “heat exchanger”. That is, it exchanges excessive heat from the engine to a place where it is unobjectionable.
How does an outboard cooling system work?
Water is drawn through the water pump from the lower unit to the cooling passages in the heads and block to the “thermostat valves”. If the valves are closed due to being below “opening temperature point” water will not pass through the heads and block and by-passed through the lower unit and exhausted (some outboards use pressure control valves to prevent excessive pressures).
If temperature rises above “opening temperature point”, water will pass through the cooling passages of the heads and block. Heat will be transferred between the surfaces within the heads/block and the once through cooling water. The heated cooling water will be expelled through the lower unit. Once enough heat is removed, and drops the temperature of the cooling water below the “closing temperature point” of the thermostat valve(s), the thermostat valve(s) will close again.
Why is an outboard motor not cooled sufficiently?
The above cycles will continue keeping the temperature of the engine within acceptable tolerances under various conditions. However, there are two reasons why an outboard motor is not cooled properly. Generally, they are insufficient cooling water flow (several reasons) or fouled heat exchanger surfaces one reason).
Insufficient cooling water flow
Reasons for insufficient water flow can be:
1. Poor water pump performance
2. Clogged water passages
3. Improper thermostat valve operation (closed or partially closed)
4. Leaks in cooling water supply to cooling passages
5. Pressure control valve stuck open
Reason for fouled heat exchanger surfaces can be:
1. Accumulation of deposits on heat exchanger surfaces (note that increased heat exchanger surfaces temperature will increase the ability of deposits to “stick” to the surfaces, as will low flow).
What do water temperature switches do, and how do they work?
So, I thought I'd put together what I thought about how an outboard cooling system works. I also thought of how valuable an infrared thermo gun is worth in determining the performance of a cooling system.
I know different Yammies are "piped and sensored" differently, but would appreciate some input to what I have put together so far.
This page one of a draft. If some of you want to comment by placing your comments in red via quoting this, I would appreciate it.
What is an outboard motor cooling system?
An outboard water cooling system is a once through “heat exchanger”. That is, it exchanges excessive heat from the engine to a place where it is unobjectionable.
How does an outboard cooling system work?
Water is drawn through the water pump from the lower unit to the cooling passages in the heads and block to the “thermostat valves”. If the valves are closed due to being below “opening temperature point” water will not pass through the heads and block and by-passed through the lower unit and exhausted (some outboards use pressure control valves to prevent excessive pressures).
If temperature rises above “opening temperature point”, water will pass through the cooling passages of the heads and block. Heat will be transferred between the surfaces within the heads/block and the once through cooling water. The heated cooling water will be expelled through the lower unit. Once enough heat is removed, and drops the temperature of the cooling water below the “closing temperature point” of the thermostat valve(s), the thermostat valve(s) will close again.
Why is an outboard motor not cooled sufficiently?
The above cycles will continue keeping the temperature of the engine within acceptable tolerances under various conditions. However, there are two reasons why an outboard motor is not cooled properly. Generally, they are insufficient cooling water flow (several reasons) or fouled heat exchanger surfaces one reason).
Insufficient cooling water flow
Reasons for insufficient water flow can be:
1. Poor water pump performance
2. Clogged water passages
3. Improper thermostat valve operation (closed or partially closed)
4. Leaks in cooling water supply to cooling passages
5. Pressure control valve stuck open
Reason for fouled heat exchanger surfaces can be:
1. Accumulation of deposits on heat exchanger surfaces (note that increased heat exchanger surfaces temperature will increase the ability of deposits to “stick” to the surfaces, as will low flow).
What do water temperature switches do, and how do they work?
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