I also have done for some customers as Dean is doing. The -8 line works well. Really cools the back of head down quite a bit. I dont dump them over board, I do that using a blow off valve on the sea strainer. Merc I think made a blow off for its motors a few years ago. It fits inline on the side or back of the motor. Do you have a transom mount pickup or just the drive?

I also had temps that would go up to 170 and then drop down to 140 within a few minutes.So I ran a 1/2" line off the rear of the manifold and it completely stabilixed my temp at about 130.I have a 142 thermostat and I have drilled holes and all but for some reason,maybe aluminum heads,the only thing to work was the dump.I also had high pressure but the merc valve that US1 told me about worked perfect for that.I have the CMI E-Top headers,does any one know how much water they can actualy flow thru them?In other words I know there is two one inch hoses per header,I am only using the lower hook up and not the top.It seams like there is no way two one inch hoses could dump enough water out those little hoses at the end of the tail pipes.

Thanks Nordic95

Did you run the 1/2" line from the rear to the front of the intake, same as the the other guys?
Mike

No I took 1/2" line and dumped it over board.Right now for testing reasons I have it tied into the 1" line for the Merc. water dumps I have out the side of the boat.Everyone thinks its my bilge pumps running all the time and they run over to ask if the plug is in.Now that I know it worked great for temp control I will add two dumps out the back of the boat and let it dump onto the drives for extra cooling.

Nordic95

so you can't just run a line on the back of the intake around the dist. to the othe side of the intake tying the back or the engine together

In my case the two 6AN hoses run to the front crossover heads were removed and inspected before intallling . Valves showed hot on all four corners number 7 cylinder being the worst. Number two was a close match to 7. Also noticed the head gasket the lower water transfer hole in the block didnt match with the head on mumber 7 and no 2 cylinders at least in my 88 block havent check some of the new stuff. I ground out the block so the holes were not restricted as the others are not. Upon runing this combo with then ith the wwater to the front crossover found stagger jettig was no longer necessary and all plugs read the same. The engine ran a bit hotter at idle and low no wake speeds but within normal range as the boat speeded up temps would go down slightly bassicly the opposite of before the mods. Heads were later removed and valves all looked the same.

I am in the middle of making this modification now.. I would rather not drill into the back of the boat.. If I run an 8an line from rear to front on each side, where do I plug in the sensors? Water Temp, High temp buzzer and Water Pressure?? thanks

I'm running an MPI intake and you can't drill them so I tapped into the back of the heads and dump mine on my outdrive. fixed my pressure also.

I've been followong this thread. I'm building a 400 sbc with a weiand 177 would this work for me? it is a siamese block which does not circulate water between cylinders. so I have had cooling problems on #7 and #8 cylinders in the past in n/a application on my last engine went to closed cooling and 14lb cap still a little on the hot side on #8 cylinder. some of my circle track friends run a line between #7 and #8 accross back of block. also brodix and dart have manifolds that are tapped on all four corners from factory,evidently for that purpose

+1