Reply With QuoteThat red heater hose is pretty strong...rated to 300 psi I think, but I blew one out on my boat...scary!! I added a pressure regulator to my system for some extra security...
Excessive water pressure from the pump feeding the engine block will force water past the head gaskets. Check the water pressure in the block at full power. It should not exceed 7 psi.
Radiator caps haven't been at 7 lbs in decades. I would think an engine should handle 15 lbs with no problems. 150-200 psi? Damn, I guess those old red heater hoses alot of us use are alot tougher than I thought....MP
That red heater hose is pretty strong...rated to 300 psi I think, but I blew one out on my boat...scary!! I added a pressure regulator to my system for some extra security...
The factories that built these old jet boats all plumbed the boats pretty much the same and didn't use anything fancy (pressure regulator's, overflow valves, etc...) whatsoever and they last decades that way. Proper ball valve adjustment is mandatory, start with the valve open about 1/4 - 1/3 and adjust the valve to get the engine to the temperature that you want it to run at. Unless you've got MAJOR HP you shouldn't run into any problems, ever. IMO
That may be true, but I still dont like the idea of running 200 psi is places where it was never intended to reasch over about 30...I'll keep my regulator, thanks
Remember...the trick to dropping block pressure is to make sure that you have the same amount of water exiting the block as what's entering the block.
I'm running 5/8" hose in and two 5/8" hoses out...I too run the bypass regulator as well as a thermostat kit and I probably could restrict it down some on one of the dumps as my system seems to be a little bit too free flowing (can't get the engine temp around 160 like I want to).
Just making an emperical observation here - All of the gauges for water pressure from VDO, Autometer, etc for jet boats go 0-30 PSI.
Assuming it has enough gauge to show too low and too high of pressure, and assuming they knew what they were doing when they designed the gauges, then I would say you want between 7 and 22 PSI.
Given I can get radiator caps in 7, 15, and 19 lb for my engine, this makes perfect sense... to me anyway....
I have a mild 455 with log exhaust that had a problem with some milky looking oil in the valve covers. I was concerned about overpressurization, leaking gaskets, etc. and used this to see how much pressure was actually getting through the gate valve:
http://www.***boat.com/image_center/...age_Valve2.jpg
The gauge was 10 bucks at Home Depot, Watts Model IWTG. I have tested it many times since then, and never got over @ 17-18 PSI. I closed the gate valve a little to increase the running temp, and the milkiness is gone. I think the milky oil may have just been condensation from running too cool.
I see a lot of people here referring to "how jet boats ran for so many years without pressure reducing valves, etc etc"...
Well one must remember that back in the day pumps were not being ran with as tight of clearances (some pumps were being ran with thrust clearances of as much as .150 - .200"), they weren't moving near as much water, much lower intake pressures, engines weren't running near as much horsepower/torque...the list goes on. Since we've been tightening up our pumps, beefing up the HP/torque of the motors, etc etc...intake pressures have drastically increased compared to what they were back in the day.
The only issue with running a gate valve at the inlet is that it not only reduces water pressure, it also reduces water volume as well. If you turn it down too much, you won't have enough water coming into the block to completely fill it, which will make the heads run hot at idle.
However...this is where it gets funny. In order to create pressure in the block...you have to have at least enough water to completely fill the block, then have water still coming in on top of that. So if you have any kind of pressure in the block, you obviously have enough to fill it.
If you're not running the pressure relief, I would say set the gate valve so that the engine idles at the temp you want it to, then check the pressure. If you have pressure at an idle then you have plenty of water to fill the block. If no pressure, turn it up little by little until you see 1psi at idle, regardless of if the idle temp is too cold or not. The point here is you want enough water coming in at an idle to fill the block so that your heads don't run hot.
Then do a WOT pass and see where you're at pressure-wise. If it's set for 1 psi at idle, but way too high at WOT, then you need a pressure relief valve. Or if you're only running one overboard dump, consider installing a second dump to relieve the pressure at WOT. You'll have to open the gate valve a little more at idle to achieve that 1psi of pressure to fill the block at idle.
If with 2 dumps and the idle pressure set at 1psi and WOT pressure is still too high, definitely install a pressure relief valve.
Please define intake pressure...My jet will not expell water until the engine fills up as the outlets are in the top of the engine, as are most I've ever seen......I still say a well assembled/gasketed engine should not leak water. Even without a pressure regulator. If you think the "tight jets" are a recent modification, just consider back when alot of the jet makers were also fielding racing teams..........MP
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