Interesting F300UCA

[pstephens46]

On another thread OP and I both searched for a poppit/PRV for this motor.
Damned if either of us can find it.

Another case of a Yam isn't a Yam.....?

[boscoe99]

You are looking for that which is not there.

The 4.2 liter block does not use a pressure relief valve.

Why?

[pstephens46]

Guessing the passages on that big bastard are large enough to handle the surge of pressure. Rod may hate the F350 but I am not sure I would want to wrestle the 4.2 either.

[99yam40]

I have a feeling the pump cannot pump too much water to cause a problem

[rodbolt17]

just as the old inline mercs, Yamaha engineers decided the 4.2L did not need a water pressure control valve.
it appears to work.

I do have a 4.2L long block coming.

gotta do yet another powerhead.