manifold check valves

[174ben]

can anyone tell me the purpose of the black plastic style t fitting/check valve mounted on the bottom side of each manifold? 5l mpi mercruiser

[mmwjr]

A picture would help but I believe you are talking about the coolant elbow with a wing nut to drain the exhaust manifolds for winterization.

[174ben]

https://www.maxumownersclub.com/foru...1&d=1696231441

thankyou for the reply this is the valve. im fitting new stainless marine torque manifolds and have been supplied a t piece to replace the check valve. wondering if the check valve could or should be replaced with the standard t piece.

[mmwjr]

I’m not familiar with this style, is your engine equipped with a single point drain system for winterizing?

[174ben]

I’m not familiar with winterising. I’m in Australia and we don’t get freezing conditions… this is the only port/hose connection coming from the bottom of each manifold. There are no “blue” plugs in this area.

This valve closes when I blow through it from the bottom.

[mmwjr]

Is there a hose on the bottom nipple and does it connect to a similar piece on the front of the engine which would be the single point drain?

[174ben]

Yes it goes to a block with about 4 hoses on it

[mmwjr]

That would be the single point drain. It does hurt to use these on the new manifolds. If not you’ll need to block off the unused port.

[174ben]

Thanks for that. I have researched single point drain and you are correct that is exactly what I have. If a tee piece is used instead of a check valve there would be cooling water entering the bottom of the manifolds all the time. My understanding is the check valve is there to stop this whilst allowing manifolds to drain when needed.

[shrew]

Mercruiser/Quicksilver 863786A1: Exhaust Manifold Drain T-Fitting

Check valve prevents water from back flooding.