I have a 78 Challenger with 460 & a Dominator jet. I am having problems with the boat overheating. Weird for a jet boat, but an issue never the less. The way the water system is set up now, I have a ball valve on the inlet from the jet that is open full, then I have 5/8 SS line that runs to the front of the motor then “T” off and ran to the water pump plate (inlet) right & left. Then from the manifold, I have a block off plate at the T-stat housing, but just below that is a ½ outlet that runs to the Bassett T valve, then to my twisties. Next to the ½ outlet is a 5/8 outlet that runs to the stern transom then is routed up to the front seat to a ball valve, then dumped overboard.
   I guess the theory of the valve at the seat is to control the temp manually, but now I have it open full time and I am getting maybe1-2 lbs of water exiting the boat. The headers are working ok, but it does seem like I am getting too much water when running at 3k or so. At idle it seems to be trickling out of the dump, and when I am running about 3k out comes out better, but not much better. At 4 k the flow doesn’t increase and it temps up to 220-230.
   I just recently pulled the motor and had to replace a few rods due to hydro locking from an intake leak. As freakish as it was, water rested on the intake and leaked down to 2 & 4. I pulled the freeze plugs and found the block packed with sand. I dug 98% of it out which was equal to a coffee can full of sand from both sides and some from the heads and re-plugged the motor. The heating problem was evident from before the rods, and seems to be getting worse now. When I put the head gaskets on, I made sure all the water jackets lined up and also the same for the new intake gaskets.
   My next move is to pull all the lines off and make sure they are clear, then to disconnect and plug the header lines and remove the freeze plugs and flush the motor out with a hose while NOT running. My question to you is this, what is the possibility of the jet not producing pressure for the inlet, yet the boat seems to drive and plane fine? Could it be cavitating at the inlet? If not, what do you suggest that I try next?
 

it seems as if the hose might be to small, i have 1" lines all the way from the jet to the motor to the headers

what kind of valving are you guys using? I am pretty sure there is a restriction, but the lines are way different from my other boats. Are you running pressure reliefs?

rodbender , very unusual for a jet boat to run hot ,is this all the time ? or at idle etc . First verify the actual temp, if you can borrow a infa red "point and shoot" thermometer and check the fronts of the heads if you need help diagnosing this call me ! Tom

im not running a pressure relief valve. i have a Lowes brass "t" that has 1" push on fittings in and i have no problem, alot of water comes out of the headers on the trailer but no over heating, and the motor just shit out with a spun rod bearing and i drove it for the whole weekend up at lake san antonio with about 10 psi of oil pressure at WFO, still runs and never got hot. Good luck, my .02 is keep it as simple as possible and there is no need for a $100 valve

If you get the valve from the marine shops you'll pay out the ass for them, but from McMaster Carr they're about $50. Part #9763K12 from McMaster Carr. http://www.mcmaster.com

With a relief valve and 2 dump lines from the motor you can run the water wide open, eliminating the chances of getting hot spots in the heads. However, your motor will run too cold like that and you'll need a thermostat to get it up to 140*. But the beauty of this setup is that your temperature doesn't rise and fall with pump speed like it does with the gate valve.

For header water, plumb one of the fittings on the water crossover on the intake manifold to a gate valve, and the other side of the gate valve to your Bassett T valve. 5/8" in, 5/8" out. With this setup you solve the problem of fluctuating temperature/shock cooling and water in the oil.

 Thanks guys and i will check out the gaskets just to be sure, but i think i found my problem. After back flushing the motor, clearing all the lines, and still scratching my head, i remembered that when i swapped carbs, i never cjhecked the jetting. i pulled a plug and they were white. I should have the carb back from PC in Ontario today and i expect this to solve the problem. It also might explain why i was getting such great gas milage!

i will keep you posted~

As for the carb, lean is an understatement. The carb that i put on was set up for a 350 crate motor. Dude at PC said himself that re-jetting should solve the heating. \

After taking all my hoses off and making sure they were clear, I re-installed them and hooked a hose to the inlet at the jet. Then disconnected the headers and capped it off at the mainfold. As i ran water thru the motor it seemed to flow fine. I did however re-routed the dump so it was just going overboard instead of running to the front seat ball valve and overboard.

As i said before, when i pulled the motor i opened up the freeze plugs and found the motor packed with sand. i cleaned it all out real good as well. 

What makes me think that it is all carburation is that when i bought the boat it had a 830 holley on it. the secondariy pump was frozen and the carb was in bad shape, but i ran it and I didnt have a heating issue. It wasnt until i dropped the motor, fixed the rods, cleaned the sand out, and installed the new carb did it start heating up. This leaves me with three possible scenerios.
1) The head gaskets are on worng. (I will check those tonight when i get home)
2) The carb is the culpret and that will fix it self when i put the re-jetted carb back on.
3) There is a blockage in the motor. (But i flushed it out already and was clear)

 

No, the valve was clear, but by by-passing it i was able to cut off 12" of hose and (2) 90 degreee fittings, needless to say they were 1/2".

When i talked to the dude at PC Carbs he said that there is a huge difference in the way you set up a jet boat vs a car, and that the 460 will require much more fuel than the crate 350. Since carbs are pretty greek to me, i guess i will know when i float this week.

i just checked the head gaskets and they are on right, but i am really glad for that post because that was in the back of my mind and i didnt want to pull the he4ads to find out! Thank you!

If this doesnt do the trick, my next step is to pull the freeze plugs and douche the motor just like before and see if there is a blockage. I took out a coffee can of sand before, I cant imagine that it is full again after only a few short trips.

Quick update on the carb.
i just got it back from PC. They bumped the jetting from 71 to 76 & 80 to 83. Is this significant to cause a heating issue?

What size ca are you running? The duration at .050 has more to do with fuel jetting requirements than CID.. I will assume they asked you about your cam duration.

That is the one thing i didnt know about the motor, but i expect it to be a small leap over a RV cam. Nothing remarkable at all so i am sure it is close now.
As i put the carb on last night i re-tourqued the intake down and found that 4 of the bolts were hand loose. In addition to that, the mid plenum gaskets were shot so i replaced them as well. I am pretty sure it was sucking air at the intake in one spot or another. I will run it tonight and further check for leaks, and i may just R & R the intake gaskets to be sure.

I spoke with Tom last night about this problem and he seems to think that i may need to replace the wear ring in the jet as it may be a pressure issue. GREAT! so much for a turn key boat.... I should have known better. The jet seems good though, it tops out at 5k RPM, comes out of the hole great with no cavitation from idle to WOT. I guess time will tell!

I have an update to the heating issues.

Dropped in Wednesday night in Topoc and ran for a while. It was still heating a bit at higher RPMs so i backed the timing off a little and that cured the problem while running. but at aidle, i am still heating and i have very little flow from the dump. Other than that, the boat ran great. Still looks a tad lean, but ran good never the less.

Before i jump into the jet, i will pull the freeze plugs and flush the motor real good to make sure I dont have a restriction. The jet feels weak, but i have had worse and they didnt heat up like this.

Maybe try removing the bowl on the pump and check if it is obstructed from the other side of the inlet.

Oh Shit (no pun inteded). But the above post sounds like some sort of deep cavity search.
Sorry off topic.
T.J.

ooops!! Can't type for shit sometimes!