pump psi at idle
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pump psi at idle

  1. #1
    Senior Member
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    Default pump psi at idle

    I was working on the carb tuning on the ramp, and noticed the temp was 180, which is higher than I have ever seen it. I found that my relief valve jam nut had backed off and so the adjustment was out of wack. Fixed that, and the temp was still 160ish idling and would drop to 140 when revved up to say 1500 rpm. It was a hot day and the water was quite warm, like bathwater. At idle (750 rpm) the gage on the pressure regulator was bouncing around 2-3 psi, 1500 would bounce 6-7 psi, and would hit 10-12 psi at 2000 rpm and up (I have it set to start relieving pressure at 10 psi, so at 2000 there is a slight dribble of water coming from the regulator dump). From the typical comments, people have a hard time getting the temps above 130-140 so is my pressure low at idle? or typical?

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  3. #2
    Jet boat service
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    Default Idle PSI

    Slim, there are a few variables here, like,how is your engine plumbed and how old is your jet. Has it been rebuilt lately? Jets will start to lose some idle pressure as they get old and tired. If you have thru transom exhausts then you are dumping engine water with two lines and your pressure numbers will be lower. Personally, I like to run around 900 to 1000 RPM at idle to get a little more water into the engine and increase manuverability at idle. Your motor is not over heating, 180 is fine but you want to avoid wild temperature swings. Jim

  4. #3
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    Default Ramp running

    While tuning on the ramp you will heat up a bit.....Like he said, 180 is not off the scale. However, be cautious.... If you shut the engine down the water will run out down to a certain level in the engine. Now you have a HOT engine, 1/2 or less full of water. So, now you restart the engine and blast lake/river temp water into a hot engine. It takes a while for the water temps to equalize, so some cast iron is going from HOT to COLD in a split second, not a good thing... So, either allow the engine to cool, or don't interrupt the water flow unless you can close a valve and keep the hot water in the engine.....I know, I know, everyone does it, even while on the water during "shut off" time, but it is similar to adding cold water to a hot radiator on the highway, and you can hear the water thumping and steaming up inside the engine........AND yes, I have seen cracked heads and blocks that could only be a result of hot, to cold, too fast.... Ray
    LOUD BOATS SAVE LIVES

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  6. #4
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    Default

    I tried to reply earlier but my computer dropped a deuce on me.
    OK so I do have a thru transom log exhaust with twin dumps, so I guess I am going to be at the low end of the pressure range.
    My water line routing is the typical pump -> relief valve -> tee -> 2 lines into log -> 2 lines exit other end of log -> 2 lines enter engine blockoff plate -> 2 lines exit engine at thermostat housing (no thermostat) -> 2 lines feed into risers -> dump into exhaust

    My pump is definitely not fresh, the leading edge of the impeller is a bit dinged up, and I have never had it apart to check things closer. I am assuming I have an A impeller. What kind of pressure "should" I be seeing assuming a fresh pump and A impeller, at idle RPMs? This may be motivation to dive into the pump, although the old lady has me on a tight allowance.

  7. #5
    Senior Member sleekvino's Avatar
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    since you have an old lady and a jet boat its time to start hiding money. Break Out Another Thousand.
    PORNO RACING INC WHERE ITS "HARD" TO WIN

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