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Thread: sea pump pressure?

  1. #1
    Badburn
    25 eliminator, 509 BBC, 5-1/2 inch water pump pulley, 5 inch crank pulley. I keep either exploding the 1-1/4 water hose, or blowing it off the barbed connectors. Only happens at high speed and rpm's. Anyone got any ideas besides don't drive fast? thanks.

  2. #2
    BDMar
    I assume yo have a low water pickup? That is typical for a cat to have extremely high pressure at speed. Double clamp the connections and put a gauge on to check the block pressure. You will probably end up with a pressure relief valve when you see how much block pressure you have.

  3. #3
    Badburn
    My water intake is on the nose of the drive(imco 3 inch short). Who makes a pressure relief valve? I found one from hardin marine, but I think it shuts the water off completely at low pressure like for an intercooler. the description is pretty lame

  4. #4
    BDMar
    I think you can get them from McMaster Carr. Get an adjustable one with at least a 1/2" pipe threads. Set it to about 25 psi and tee it into the intake side of the sea water pump, and dump it out the transom.

  5. #5
    Badburn
    I'll check into that one. If I understand your post right, you think the high pressure is coming from the water intake, and not the pump? Damn I wish I had a pressure guage

  6. #6
    BDMar
    It is not the pump, it is a high volume ot high pressure. The only way is if you had a restriction on the exit side of the water system.
    We have experienced this problem with Imco lowers and cats numerous times.
    If you still have the stock thermostat housing and re-circulating water pump it will add to the problem.

  7. #7
    Badburn
    I ordered the pressure relief valve from Mcmaster Carr.
    I did blow the hose out of the front of the drive one day too, right where to goes from the gimbal thingy to the transom. What you are saying makes sense.
    One other guy told me to restrict the hole in the front of the lower unit, and or add another water exit from the motor. What do you think about that?
    By the way, Thanks. Your input has been very helpfull on this thred as well as some of my other bonehaed threads.

  8. #8
    BADBLOWN572
    One other guy told me to restrict the hole in the front of the lower unit, and or add another water exit from the motor. What do you think about that?
    You can do that, but if you are going to plug up the front holes on the drive, you better make sure that you have enough water flowing at idle. If you don't, you will be hurting yourself. That is why the pressure relief valve is great. It will still allow max water to pass through the drive, but it will bypass anything over the set PSI limit.
    At idle, your raw water pump is actually sucking up the water from the drive. If you reduce the size of the inlets, you really reduce the amount of water supplied and could possibly cause your motor to overheat. Your only problem is on the top end where the boat is forcing too much water into the drive. A pressure relief valve will help.
    Another thing that you may try as well, is a T-bolt style hose clamp. The standard band clamps work, but they are not as good as you may think. Any place that has a high pressure line entering the motor, I use the T-band clamps. They are cheap insurance to make sure that the hose doesn't blow off. Just make sure that you don't tighten them down too much and break the water pump housing or the neck coming off of the gimbal.
    http://www.clampco.com/products/images/tbolt1.jpg
    Good luck!

  9. #9
    BDMar
    I ordered the pressure relief valve from Mcmaster Carr.
    I did blow the hose out of the front of the drive one day too, right where to goes from the gimbal thingy to the transom. What you are saying makes sense.
    One other guy told me to restrict the hole in the front of the lower unit, and or add another water exit from the motor. What do you think about that?
    By the way, Thanks. Your input has been very helpfull on this thred as well as some of my other bonehaed threads.
    Your welcome! Badblown is right. I don't reccomend reducing the pickup size. We have done it, but in very small increments until we got the desired results, and it did make the pump work harder shortening the impeller life.
    Adding another exit is not a bad idea either. That will lower the block pressure which I have seen as high as 55 psi in applications like yours. Way too high. Start with the relief valve between the gimbal and the water pump. I would still suggest putting in a block pressure gauge to the dash. It will not only tell you if you need to bleed off pressure from the intake, but it is a great tool to tell you when the impeller is ready to be replaced, if weeds are clogging your oil cooler, or if there is a baggy over the pickup slot, etc. Adding water psi gauges is the first thing I did after buying my boat and I keep a very close eye on them when running in the Gorge.

  10. #10
    Badburn
    I went to the delta yesterday, hooked up a temporary spare oil pressure guage to measure water pressure in the block, Saw 60 PSI on the guage, then the hose exploded again! LOL I wonder if one bypass will do the trick? Waiting for the UPS man.
    If I Rev the engine to 5000 rpm in neutral, the pump makes 18 PSI. This confirms that it is the water pickup creating the high pressure. Nice call BDMar.

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