4.108 Vented loop

[CYQK]

Finishing a rebuild on a 4.108
Seen both where would you install a vented loop
Between the intake and the raw water pump or downstream aft of the heat exchanger

Thinkin aft of the heat exchanger would be better but this one didnt have one before so I want to get it right

Thanks
Gary

 

[Joe]

Definitely not in front of the pump.

From Forespar notes on their vented loop product:

All vented loops are designed to have fluids "pushed" through them. If you try to "pull" through a vented loop, you will pull air into the line and not move the heavier fluid.

 

[CYQK]

Thanks for the reply Joe

Ya that drawing is exactly right where the loop position could be before the heat exchanger the other is at the mixing valve. Which position is better?

 

[Joe]

Thanks for the reply Joe

Ya that drawing is exactly right where the loop position could be before the heat exchanger the other is at the mixing valve. Which position is better?

Check with your engine manufacturer. That's way to technical for me... I just know that you can't suck water through a vented loop, it has to be pushed.... anti-siphon also means "anti-suck".

 

[Scott T-Bird]

What's the purpose for a vented loop? I don't recall seeing any mention for it with my Yanmar either before or after the exchanger.

 

[Joe]

What's the purpose for a vented loop? I don't recall seeing any mention for it with my Yanmar either before or after the exchanger.

Scott, here's something that might help: the previous image I posted showed the air vent between pump and heat exchanger.... this one shows air vent between exchanger and exhaust pipe.... but it's all the same circuit.
https://www.tidesmarine.com/pdf/VentedLoop_Install.pdf

A vented loop (anti-siphon system) is used when an engine’s exhaust port is located below the waterline. When a
marine engine is shut down (and the system DOES NOT have an anti-siphon valve), raw water continues to siphon into
the exhaust system until it reaches the same level as the waterline in which the vessel rests. If the engine is installed
below (or at) the waterline, this water will flow back up the exhaust pipe and into the engine itself.
The vented loop closes when the engine is running (under raw water pump pressure) and opens when the engine stops,
allowing air into the system which prevents water from moving back through the exhaust system and into the engine.

 

[CYQK]

Good post Joe thanks

Well.......quizzed the gurus at FLL and on a 4.108 the loop should be at the mixing elbow

 

[Scott T-Bird]

Oh, I guess it would be for redundancy. The gooseneck should provide the primary protection, as long as it is high enough and following seas don't overwhelm it.