Just bought a 75 Southwind 20ft boat with a 460 and 12J/c pump. The previous owner was nor the sharpest knife in the drawer, based on a few of the issues with boat, but it was purchased dirt cheap as a project and things are expected. Doing a bit work on the pump right now, mainly sealing all the water leaks, and removing tons of silicone. Since this boat is a bit "fractured" shall we say, I want to be the cooling is routed correctly. It has a hose coming from the water inlet on the pump, to a tee, that splits off, and goes into the front cover (black hoses). Then 2 hoses go from the front of the thermostat housing, to the fronts of the log manifolds (red hoses), and then, from the back of the logs, to the risers. The temp sender is in a plate on top of the thermostat housing.
Does this seem correct?
Not exactly correct. Water should go to the front of exhaust logs first after splitting off from the t. Comes out of the back of the exhaust logs and goes to front cover. Water exits the engine at the top from the thermostat housing and goes to the snails where it goes back to the lake. Going through the logs first preheats the water so you don't have ice cold lake water dumping into the block.
Local lake water is about 68-80
What should engine temp be, about 155
the way it's set up is just fine. if lake water is 80, water temp out will probably be 120-130. it is a single pass system. which means you are taking 70 or so degree water, heating it up 40-50 degrees before it's discharged. you do not need to choke flow down with the only objective of trying to raise exit water temp. water temp in a single pass system like this is NOT indicative of actual engine temp. oil temp could be 80-100degrees higher than exit water temp, and is much more indicative of engine temp.
in a system like this, heat removal is based on Tout - Tin X flow rate. to elevate the Tout value, just cut back on flow rate.
you do need to be cautious of engine waterside pressure. the pressure provided by the jetdrive will vary with rpm. i.e., max rpm = max supplied water pressure. minimum rpm = minimum pressure. pressure will correlate to flow rate. i.e., if you're idling for an extended period and you see water exit temp rise, it's because of inadequate pressure/flow. increase rpm a bit, and you'll see temp start to decline.
also, it is not advisable to run the thing dry on the trailer. the hoses running from the risers to the transom can get very hot very quickly. if those hoses start to fail, you could have a problem. if you hook up a hose to the thing to run it on the trailer, make sure the bow is raised so the boat is sitting like it would be in the water. reverse flow of water in those risers can damage the engine, and with the bow down, that's a risk.
If you ask 10 jet boat "experts" about cooling water plumbing you're likely to get 7 different answers... I have never been a fan of "Pre heating" the water through the exhaust logs, but then again I don't use a jet in COLD water like some here might. I think you can go back to the age old saying, "if it aint broke, don't fix it"....
Biggest problem to really "dialing in" the cooling system is the various places it will be used. What works really well in a mountain lake, will likely over heat in a desert lake with a 1 mile "no wake" zone....
I will caution you about restricting "IN" flow, vs the better way "OUT" flow.... Another caution, reading water temp is misleading at times. Fast moving water takes very little heat with it, and even though the temp gauge barely gets off 100*, the actual temp in the combustion chamber will be a lot higher. It was mentioned to monitor OIL temp. An oil temp gauge will tell you a better story than a water temp gauge in an "open" system...
AND.... Do not figure the first time out will be a good day to take the family out for "a day on the water".. When you think the boat is ready take one or two friends and PLAN on having problems. Little shit, some of which can be easily fixed, and other issues that will need major work, AT HOME.... I learned a long time ago that the family "waiting" on the beach can be very stressful, so get it right and then take the family out and every one has fun, even YOU..
Good luck and remember, boating is suppose to be FUN....
My manifolds are not set up like that. (see posted pics)
and that's ok. either way works essentially the same. if you were running in 35 degree water, preheating might be preferred. you aren't doing that. since you're running in 70+ degree water, the way you have yours set up will work just fine. your cooling system is about heat removal, not water temperature.