So I have 2 5/8 hose coming out of the t stat. One goes to the dump on the back of the boat and the other goes to the ball valve (in the engine compartment) then the the headers. My question is, does the hose from the motor to the headers need to be that big or can I go 1/2. I'm going to run the valve under my seat now and the big hoses are hard to hide. If I can do 1/2 do I have to keep the dump 5/8 or can that be smaller.I know this is an easy question to answer by someone here, I just don't know what sizes they should be to start with.

So I have 2 5/8 hose coming out of the t stat. One goes to the dump on the back of the boat and the other goes to the ball valve (in the engine compartment) then the the headers. My question is, does the hose from the motor to the headers need to be that big or can I go 1/2. I'm going to run the valve under my seat now and the big hoses are hard to hide. If I can do 1/2 do I have to keep the dump 5/8 or can that be smaller.I know this is an easy question to answer by someone here, I just don't know what sizes they should be to start with.

What is your estimated horsepower?

It makes all the difference in the world.

Also, you didn't mention what headers,  over transom, through?

You can run a fairly small line to the header control valve, 1/2" should be adequate. The dump line is dependent on cooling requirements, horsepower and what fuel?

If you can describe your system a little more, I'm sure your question can be answered adequately.

GT

Thanks gt. It's a mild 454 probably 400 maybe a little more, nothing special and nothing like what you guys are running. They're bassett ot headers and it runs cold I have to play with the valve after the pump to get it up to temp.  I have another question if you don't mind.  What pressure  should the relief valve going to the motor from the pump be and where should it be in the system. I'm trying to see if this thig has the right set up. Thanks again

The valve should relief at about 20PSI.

If you have it set up properly it should never relieve.

There should be a gate style valve at the pump,  adjust it so that the idle water temperature is about 150°F.

You should be good.

GT

Thanks man

Ain't no Thang brah.

GT