Has anyone else seen motors plumbed so that the water runs through the headers before going to the block??? The old eastern express skater had this setup. Running no stats and the owner claimed the water was always between 140-180. Also said the water was pre heated before entering the block so there was less shock cooling.

I had several boats like that. They were never a problem.
Steve

Can you explain in depth how it was plumbed???

Did it all the time.You run into the water inlet's in the bottom of the manifolds,or headers.You must use a y fitting on the water hose coming from you sea water pump in order to do this.Where the water comes out of the top of the headers instead of going with the small jumper hose to the riser,you take those hoses and go to the input holes in the front of the block,then were the water comes out of the block at the thermostat housing you take that water and put it to the riser water holes that empty the water out the pipes.In the case of stock merc manifolds you have to put a block off gasket in between the manifold and the risern and take out those two plugs in the riser and top of the manifold to run it that way. And it does work very well.JOHN SR

everybody ive talked to says this works well, so my question is, why dont you see it more often??? the engine i saw had a plate over the thermostat housing and they used the four holes (front and back) on the manifold as an exit to the exhaust. no thermostat and he said temps were always perfect. it makes sense because in reality the exhaust needs more water to keep it cool than the engine block itself....

shock cool the block or shock cool the header. Does it make a difference?

I'm say if your running a thermostat with the normal setup, when the thermostat opens it shocks the block. This setup would have no thermostat cause the water would be preheated by the headers. The headers would also have constant, consistent flow and therefore wouldn't ever get a blast of a different temp water

It gets pre-heated by your oil cooler.

How so? The temp is consistant whether at block or headers. Not like the headers are hot, then cold water is instantly introduced into them. The headers/block are always in contact with the flowing water. T-stats work same way, temp is maintained by opening/closing at a controlled rate, not a instant open full flow to a closed no flow condition. There is a transition period at any point.

I don't think it makes much of a difference was my point.

However, if you're running t-stats I suppose having 100% water flow to the header is a good thing because a bypass hose or the poppet valves can't provide full flow when it's closed.

I'm sure Mercury has their reasons.