In my learning curve of jet boats I learned something that I wanted to share so that other newbies dont make the same mistake. I changed up my new to me boat a little because on paper and in reading it made sense about having too much water pressure in my block. Per the internet I had to have 2 -10 or 5/8's return lines off my block because if I didnt I'd have way too much pressure and possible push out gaskets and I needed a ball valve to control water to my OT Bassett headers. Well I made the changes and went out this past weekend to see how it works. At first I had a gauge on the manifold that read up to 100psi because I didnt want to over peg the gauge and break it-lol what a joke. I couldnt really get a good reading Saturday because of some factors but I didnt really see the gauge move so on Sunday at South Cove the water was like glass and I got a chance to really hammer down, oh and by the way I installed a 15 psi gauge. Under full throttle I only saw 7 psi of pressure and at idle maybe 1-2 psi. So the whole over pressurization of the block article was bull on my stockish big block. What I should of done first was installed the gauge and seen what was going on and installed a ball valve going to my spring loaded t valve for the headers. Now that I have a new hole in the back of my boat for a dump I dont need I will just add another valve to shut it off or possible insert a restrictor into the hose.
After researching this again, here, yesterday, someone already pointed this out I guess if have a high rpm engine or upgraded jet you dont need this, maybe But even though its my fault for not looking here first thanks to everyone that has posted on this subject earlier. 

In my learning curve of jet boats I learned something that I wanted to share so that other newbies dont make the same mistake. I changed up my new to me boat a little because on paper and in reading it made sense about having too much water pressure in my block. Per the internet I had to have 2 -10 or 5/8's return lines off my block because if I didnt I'd have way too much pressure and possible push out gaskets and I needed a ball valve to control water to my OT Bassett headers. Well I made the changes and went out this past weekend to see how it works. At first I had a gauge on the manifold that read up to 100psi because I didnt want to over peg the gauge and break it-lol what a joke. I couldnt really get a good reading Saturday because of some factors but I didnt really see the gauge move so on Sunday at South Cove the water was like glass and I got a chance to really hammer down, oh and by the way I installed a 15 psi gauge. Under full throttle I only saw 7 psi of pressure and at idle maybe 1-2 psi. So the whole over pressurization of the block article was bull on my stockish big block. What I should of done first was installed the gauge and seen what was going on and installed a ball valve going to my spring loaded t valve for the headers. Now that I have a new hole in the back of my boat for a dump I dont need I will just add another valve to shut it off or possible insert a restrictor into the hose.
After researching this again, here, yesterday, someone already pointed this out I guess if have a high rpm engine or upgraded jet you dont need this, maybe But even though its my fault for not looking here first thanks to everyone that has posted on this subject earlier.

Just because you didn't build alot of pressure doesn't mean you shouldn't do things the right way. That's the best way to set up a boat with headers. When you get some horsepower, and started messing with the pump your water setup will already work. Even if you're only pumping 7psi through the line, you're still moving alot more water than a normal car setup when you consider the volume you're moving. If you're not seeing any water temperature rise, I don't see why you would want to restrict the water?

I run dual dumps also. This came after a very long conversation with the owner of performance jet, whose name I can't remember at the moment lol. For cooling in a jet boat certain pressure isn't needed like in a car. It's all about volume and making sure you aren't over pressurizing it to avoid leaks and milkshake etc...

i dunno i have 2 dumps and they're always shooting a steady full stream.  i have a single -10 from my pump, splits into 2, goes thru manifolds, into motor, out the top 2 dumps and out the back.

I do have O/T exhaust and I do have a nice stream of warmer water exiting both dumps. I understand my headers wont shoot water like your setup out the exhaust but I think I'm running a little thin still.

the title of this thread has to have a sig line in it somewhere 

too funny

I do have O/T exhaust and I do have a nice stream of warmer water exiting both dumps. I understand my headers wont shoot water like your setup out the exhaust but I think I'm running a little thin still.

Most jet boats run 90*-110* at idle or wide open. Typically a boat motor will have a little extra piston to cylinder clearance than a car motor, allowing for the hot piston to expand and the cooler cylinders to not expand as far. If you have a car motor in your boat then a little more temperature would be beneficial, but most jet motors are bored/honed a little extra. Also you could just put a little weaker spring in your Bassett T-Valve for the water to come on sooner, probably get one at Ace Hardware or something for under a dollar. I've never liked the Bassett valves myself, on the several jets I've plumbed water on I gutted the T-valve and ran a line up to the driver with a ball valve I control. But I also don't have a stock motor so I worry about water and reversion a bit more. I have a gate valve also on the transom to restrict water if I needed to, but the less water pressure means the less chance of getting water past a gasket.

this weekend i decided to give a single 10- dump a try on sunday i pulled one of my lines off and capped it and ran a single line just hanging off the back of the boat.  i couldnt get the damn temps under 160 even when WOT.  idles were 200.  theres DEFINETELY a huge bottleneck in water getting out of the motor compared to dual dumps and i would hit 100's.  my exhaust manifolds were much hotter as well. 


go duals.

Did you know that ideal water temp is 180°? 200° at idle is normal too.

Retested this past weekend with around 110 ambient at the lake. At idle boat never went above 135 and under full throttle temp gauge showed about 115. I actually built more heat in the engine just sitting on the beach, engine off and drinking water. And I was much happier with my oil pressure with 10w-30 weight oil under throttle at any rpms was at 80 at idle 1100 rpms I was at 50 psi vs 15w40 at 80 psi always always or not. My testing pretty much ended when my floater decided idling wasnt in its future, worked out fine anyways day was over. Next day looked over everything and removed all the plugs-looked brand new with zero color-so it was very lean- compression test was excellent same straight across the board- and removed carb only to find secondaries on carb rusted and inop. So here's my chance to ditch the 600 and go with mechanical 750. Now to figure out if I square the jetting off on the new carb or not-more research- but I live for this stuff.

After reading this thread I still don't know what your having trouble with. Is it all about what your seeing on your gauges or is the boat running poorly? I see you read about over pressuring the system, I did too and thought some similar things that you did. After futher research I decided I don't need to worry about this. I did set up my engine from the ground up to do exactly what it's designed for - run a boat and run cold.

Wasn't so much a problem as it was questioning and me being a newbie. My back ground was drag racing and we always tried to run around 160 and wasn't sure if a jet boat with a performance type engine had to be the same, then add water cooled headers-totally new to me-and I was questioning how much pressure I should see in the block and if it was enough to cool the headers. Besides its nice to see how others think and why they do what they do.
Thanks to everyone for their input. So I'm good with running it cold and lower pressures in the block.

Keith. Too much water pressure means milkshake....blown head gasket(s)...or worse, hydro lock. Turn the water down and play it safe.

Keith. Too much water pressure means milkshake....blown head gasket(s)...or worse, hydro lock. Turn the water down and play it safe.

Agreed.

What I was trying to say though, is that maybe the temps inside the engine aren't changing as much as he thinks with the difference in outlets.

 
I agree with 74 Bonneville 100%

Hey 74 Bonneville, have any thoughts about my post under jet pumps - Fine tuning my performance jet?
Would be much appreciative