Water pressure; Looking for the real answer!
05-14-2003, 09:58 PM
#21
Dave,
Holes drilled in your thermastat can not flow enough water to lower pressure more than a few pounds. Holes are mainly for when the stat is closed.
My thought has been that the holes are more to allow the block to fill by bleeding off the air while the stat is closed at start/warmup. And also helps put 'some' hot water on back side of stat. Also consider this, if you have high pressure, it is because your stat is still closed because motor is not up to temp. Sounds like you running a crossover and trying to use a t-stat??
Did you recheck your intake bolts? All my intake leaking experience has just been leaking past the gasket, not blowing them out. So just retightening the intake should be fine. Or at least the answer to your problem if it is the problem. Then you can decide if you want to install new ones. BadDog had this same problem this spring with his new motor. Tightened intake in many rotations, all is good now. Please check this.
Holes drilled in your thermastat can not flow enough water to lower pressure more than a few pounds. Holes are mainly for when the stat is closed.
My thought has been that the holes are more to allow the block to fill by bleeding off the air while the stat is closed at start/warmup. And also helps put 'some' hot water on back side of stat. Also consider this, if you have high pressure, it is because your stat is still closed because motor is not up to temp. Sounds like you running a crossover and trying to use a t-stat??
Did you recheck your intake bolts? All my intake leaking experience has just been leaking past the gasket, not blowing them out. So just retightening the intake should be fine. Or at least the answer to your problem if it is the problem. Then you can decide if you want to install new ones. BadDog had this same problem this spring with his new motor. Tightened intake in many rotations, all is good now. Please check this.
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Last edited by US1 Fountain; 05-14-2003 at 10:06 PM.
05-15-2003, 09:15 AM
#22
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Ok...next question.....after I check and re-torque the intake manifolds.....where is the water pressure sender? I don't currently have a water pressure gauge...is there a sender already or do I need to put one on? Where is the best place to put the sender?
So...who has these valves and how can I get one? (if you don't personally have one...a manufacturer and part number would help!!)
If I don't drill a hole in the back of the boat....it sounds like I can just dump the overflow into the exhaust....will it hurt anything to dump it just to one side or how would you recommend dumping evenly into the exhaust????
Thanks!!!!
So...who has these valves and how can I get one? (if you don't personally have one...a manufacturer and part number would help!!)
If I don't drill a hole in the back of the boat....it sounds like I can just dump the overflow into the exhaust....will it hurt anything to dump it just to one side or how would you recommend dumping evenly into the exhaust????
Thanks!!!!
05-15-2003, 09:37 AM
#23
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Dave,
Pressure gage should be installed in the block. you can remove your drain plug and get a fitting with a hose barb connection instead. Any hardware will have it. Mercury makes a gage for the outboards that fits a 2 1/8 hole. If you try to dump too much water through the exhaust your exhaust will have to "fight" the water on the way out and performance will suffer. On some stock setups others have reduced the water to the exhaust for better flowing exhaust. Re read the other threads on water pressure and do a search on dump valves. Wette Vette has a rig all setup for you and has done the homework. I did my own and it took some dialing in.
Pressure gage should be installed in the block. you can remove your drain plug and get a fitting with a hose barb connection instead. Any hardware will have it. Mercury makes a gage for the outboards that fits a 2 1/8 hole. If you try to dump too much water through the exhaust your exhaust will have to "fight" the water on the way out and performance will suffer. On some stock setups others have reduced the water to the exhaust for better flowing exhaust. Re read the other threads on water pressure and do a search on dump valves. Wette Vette has a rig all setup for you and has done the homework. I did my own and it took some dialing in.
05-15-2003, 12:15 PM
#24
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Dave,
I installed a pressure relief valve last year after my rebuild as well as installing a water pressure guage. I removed a plug that was on the intake manifold, installed the sending unit and wired up to the guage at the dash. Works perfectly. Used Gaffig components. As far as the dump is concerned, I did drill a hole in the transom.
This may sound hokey, but if you are really concerned about drilling holes in you transom, another solution would be to dump through your existing bilge pump thru hull outlet. This could be accomlished by installing a tee before the outlet and reconnecting the bilge pump and and the pressure refief dump. However, to stop the relief water from being pumped back into your bilge area and vice versa, a check valve (sized the same diameter of the hose) would have to be installed on each line before the tee going to the thru hull fitting. These small check valves are readily available through Grainger or McMaster-Carr where I in fact purchased the pressure relief valve.
Hope this helps!
BTW, My pressure went from 35psi at WOT to 25psi. I can adjust the relief to any setting from 0-50psi.
Paul
I installed a pressure relief valve last year after my rebuild as well as installing a water pressure guage. I removed a plug that was on the intake manifold, installed the sending unit and wired up to the guage at the dash. Works perfectly. Used Gaffig components. As far as the dump is concerned, I did drill a hole in the transom.
This may sound hokey, but if you are really concerned about drilling holes in you transom, another solution would be to dump through your existing bilge pump thru hull outlet. This could be accomlished by installing a tee before the outlet and reconnecting the bilge pump and and the pressure refief dump. However, to stop the relief water from being pumped back into your bilge area and vice versa, a check valve (sized the same diameter of the hose) would have to be installed on each line before the tee going to the thru hull fitting. These small check valves are readily available through Grainger or McMaster-Carr where I in fact purchased the pressure relief valve.
Hope this helps!
BTW, My pressure went from 35psi at WOT to 25psi. I can adjust the relief to any setting from 0-50psi.
Paul
Last edited by pb; 05-15-2003 at 12:19 PM.
05-16-2003, 10:45 AM
#25
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Relief valves
Pb,
Which valves did you order from McMaster Carr or Grainger.Do you have a part number.
Also should the valves be located before or after the seawater pump.
Mark
Which valves did you order from McMaster Carr or Grainger.Do you have a part number.
Also should the valves be located before or after the seawater pump.
Mark
07-02-2003, 10:49 PM
#26
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TTT
Just wanted to bring this back up again as I am looking for Mercury Pressure relief valve part # as described in earlier posts.
New motor & my pressure is way high.
Thanks John
New motor & my pressure is way high.
Thanks John
07-03-2003, 06:57 PM
#27
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I've done quite a bit of testing on engines, Mercury Racing has done 10 times more. You need water pressure in open cooling systems to relieve steam. The back of the heads do not have a passage out, the water enters the front of the block, fills the block and heads, and then exits the front of the intake. The water in the back of the heads does not circulate and can become stagnet in the back. Steam can form without proper cooling. If steam forms, it will need psi to push it out.
Theres also a varaince depending on the use of a circ. pump or just the sea pump with a cross over. We do what you see in most racing applications, we bleed the back of the heads through the back water passage on the manifold. We bleed a 1/4" line right out the back of the boat through one -8 thru-hull dump. In the early stages, we installed clear hose just so we can watch the water and possible steam. You won't believe what you get out of there.
You don't truly need 25lbs of pressure, but because of the distribution of the water through the engine, the high X dimensions, the stepped bottoms, psi is very important. Some boats that have 15 will be fine, some that have even 5 will be fine, it depends on many varibles, but some of these pick up so much air, your psi reading is not accurate. You can see with clear hose the bubbles, steam, etc. coming out of the engine. So in most cases, Mercury Racing, Sterling, Pfaff, Eickert, Whipple, etc. all call for high block psi. This will eliminate some of the possible problems, will typically allow for higher spark advances or more boost, etc and overall, more reliability.
Water temp is not always a direct relation to water flow. Motors can run 90 degrees at 700hp and only have 5lbs of block pressure. Thats a huge potential problem.
Thanks,
Dustin
Theres also a varaince depending on the use of a circ. pump or just the sea pump with a cross over. We do what you see in most racing applications, we bleed the back of the heads through the back water passage on the manifold. We bleed a 1/4" line right out the back of the boat through one -8 thru-hull dump. In the early stages, we installed clear hose just so we can watch the water and possible steam. You won't believe what you get out of there.
You don't truly need 25lbs of pressure, but because of the distribution of the water through the engine, the high X dimensions, the stepped bottoms, psi is very important. Some boats that have 15 will be fine, some that have even 5 will be fine, it depends on many varibles, but some of these pick up so much air, your psi reading is not accurate. You can see with clear hose the bubbles, steam, etc. coming out of the engine. So in most cases, Mercury Racing, Sterling, Pfaff, Eickert, Whipple, etc. all call for high block psi. This will eliminate some of the possible problems, will typically allow for higher spark advances or more boost, etc and overall, more reliability.
Water temp is not always a direct relation to water flow. Motors can run 90 degrees at 700hp and only have 5lbs of block pressure. Thats a huge potential problem.
Thanks,
Dustin
07-06-2003, 07:58 PM
#28
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I am running 500HPs with Stainless Marine strainers with overpressure dump over drives. I put crossovers on motors. At WOT I get 7-10 psi water pressure from each moter. Idle shows no pressure. Water temp never gets past 105. Oil temp at WOT hits 260. When I put in new impeller, I hit more consistent 10psi. Should I check head temps etc. SHould I have thermostat or not?
