Question about exhaust water flow and temperature.

[vetplus40]

At the onset, I would like to thank those who dedicate their time to helping on this forum. Your help is simply invaluable to folks like myself who are just learning about marine engines or making a transition from other type of engine related activities.
I flushed my "thru hull" dual exhaust 5.0 yesterday and noticed a couple of things that caught my attention.
1. Flow was good (new impeller) but slightly more flow from the starboard exhaust. The port side needed about 5-6 more seconds to reach the same volume of discharge that the starboard side did (caught water in a gallon pitcher and measured).
2. Once the thermostat opened, exhausted water from the starboard side was hot, while the exhaust from the port side was a mixture of hot and cold.
I looked in my service manual and tried to follow the diagram of the flow path. Since the water inlet system is located on the port side, this might explain the hot/cold mixture, but I was hoping to find out for sure. As usual, thank you in advance for any and all responses.

 

[H20Rat]

Normal... Your boat is never 100% perfectly level, and even then, flow differences will cause what you saw.

 

[vetplus40]

Thanks. Did I have the right thoughts on the one side having a mixture of hot and cold exhaust?

 

[wingless]

There is a single raw water inlet that is split into two outlets.

On my boat the raw water / engine coolant heat exchanger splits the single inlet into dual outlet flow. This is effected by the raw water for one side making a second pass through the heat exchanger. As expected, the water on that side is hotter than the side only going once through the heat exchanger.

The raw water cooled exhaust parts must be unbolted for an annual internal inspection when operated in salt water. My salt water exhaust parts would last for three or four years, prior to my redesign. Now I flush w/ fresh water, soapy water, Salt Away and drain bone dry. My internal inspection after three years reveals these part to looking brand new. Formerly they would have horrible internal corrosion at this point, forcing a decision on continued usage. Now I think I will get indefinite usage from these parts.

 

[harringtondav]

A raw water thermo hsg splits the the flow to each manifold/riser. The starboard side is nearly in line with the supply inlet, and gets more flow at idle. The port manifold flow takes a 180 degree turn so gets less water and tends to run warmer. Under way at higher rpm there's plenty for both sides.

 

[vetplus40]

Thanks for the info. I got lucky in the fact that I delayed changing my impeller and nothing bad happened. The old one looked really bad when I replaced it.