Just wanted to tell you what i did. I run in the Hudson once in a while and here and there for longer Runs, Sometimes close to an Hour at or near WOT, My temps would rise a bit where I'd start keeping my eye on the gauge, I started over thinking and decided to check outlet water temp right before exhaust, They were very cool at WOT compared to engine temp. I put 1/2 collars in the 3/4 inlet hose to exhaust dumps to slow the water flow down. It worked. Water stays in there a little longer and seems to transfer more heat. it also could be with a slight restriction in the raw water cooling side. it is less aerated and transferring more heat out of the motor. Hope this helps someone.

what kind of material are the collars made from ?
will you test them at cruising speed on some of your running around the lake days out ?

What motor ?
What inlet position in the drive ?
What is water psi before and after using those restrictors ?

509. I never checked pressures before and after. I just had my strainer relief set. Pickup was a transom mount

Okay, so open cooling.
Factory recirculating system or cross over's ?
Does the relief relieve water same amt of time as before ?

Cross overs. And it seemed to spike/open less. I think a big part was smoothing out the flow and letting it grab more heat from the motor

Slowing water thru a block will not cool it faster because of speed by itself.. However, raising the psi thru restricting water just after the engine (by product this slows water flow thru engine)could reduce temps if it replaces air pockets and/or dead flow areas.

You get water temp? I`ve never seen my gauges move.

you have me wondering about the air pockets. I know I have back pressure but not sure how much. When I put my new t stats in the temp fluctuates then they settled after a few times out. Thought it was the t stats??

Are you running a T stat --- if so what temp T stat ? and if so what T stat housing ? does the housing have check balls in it ?