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Thread: Underheating Problem, Maybe?

  1. #11
    Racing Ray
    My apoligies to the board, not the place and I know that better than most. Since you asked Rio you divert it with a cable. The rest of your questions I think have already been answered in the posts.
    PS where is the spell checker here I can't seem to find it? LOL!!! That monkey must have taken it home with him.

  2. #12
    HOSS
    I great discussion. Where was I at? The gate valve/all other valves has been discussed here in depth. I understand why the gate is not the best way to go but none the less damn near every jetboat has one on it. Probably installed from factory. I say right on Rio and right on Racing Ray. A little diversity is good. We don`t all want to drive Ramblers. I thought this was a great discussion. I was over in the Sandbar mixing up some bullshit. Don`t recommend Bench Racers cause its lame and without tech help. Not even a good arguement. boxed

  3. #13
    rivercrazy
    Being around this board for a long time I can say one thing about Racing Ray. That guy has forgotten more about engines than the vast majority of us will ever know.
    He used to post a lot and help many many peeps around these parts. Then he disappeared due to all the crap posting on the board and the flame contests.
    Some things never change.....

  4. #14
    LVjetboy
    Not sure about the laying on of hands on each other's blowers...but I have a few comments.
    No matter inlet or outlet valve, or even if you have a valve, or a thermostat for that matter...I think a temperature gage works best for avoiding overheat. Pay attention to it, adjust so no overheat at idle during highest temp conditions, and presto, no overheat.
    I'm curious, does the hotter engine gain more power from less friction than it looses in power from less timing?
    Also wondering, does anyone have proof that running a a boat engine at say 120 degrees (single pass cooling) significantly increases wear over say, 140 degrees? Or 120 over say 160?
    Floored brought up the example of hot water through engine for machining. Assuming the shop that machines my block actually did this, I wonder how that engine temp compares to lake conditions? In other words, even if you machine the block with 180 degree water circulating, how does the mean metal temperature and cylinder bore shape compare to what the engine sees on the lake with 120 cooling temp but significantly higher internal temps?
    Just some thoughts,
    jer

  5. #15
    Mandelon

    I love this place! I don't want to add a valve to the intake....Another thing to pay attention to. I already have enough of those. Kids, friends, PWCers in my way, gauges, and how not to spill my beer while I am speeding through no-wake zones....J/K
    What temp should I be running?...
    I'm surprised the existing thermostat have issues at 120 hours, but if its shot, I guess its shot. Could have something stuck in it. As said before its a cheap part.

  6. #16
    Racing Ray
    Rio
    Thanks, it is behind us. Let's just keep trying to help our friends because that is what it is all about.

  7. #17
    Floored
    jer, if you run the block temp low then the cylinders do not expand to proper size and if you are leaning on it and building heat on the pistons then they grow to the point of possible seizure, depending on clearances your machinist set. if you were running a cast or hypereutectic piston,not in the Dragin, you are only running.0005 to .001 clearance, thats tight if the piston is expanded and the cylinder isn't quite yet. many piston mfg's can even tell you the HP loss or gains from increasing or decreasing clearances. When you set ring clearances they have recommendations for naturally aspirated, nitrous, blown,or fuel. These are all temperature based for correct clearances, too hot and they ring butt and sieze and too loose and you leak past the ring gap. I dont think that anyone on these boards would start their car and roll into the street and hammer it down, why beat up your boat. but these are just my opinion and subject to change if someone wishes to show otherwise

  8. #18
    Senior Member
    Join Date
    Jun 2009
    Posts
    10,871
    Thank you both RR and Rio for backing it down to a civil level again. My purpose here as moderator is very simple. To keep the gear head forum a tech forum and keep the bs and drama out of it as much as possible. When a personal attack sequence of posts gets going and degenerates into name calling etc. I'll step in and stop it. That is what the webmaster put me here to do. If that pisses the participants off well so be it, hopefully it will not. We have several places on Hot Boat where you can go for that if you feel the need other than gear heads.
    Also Rio, as I've explained in a PM also, I am not predisposed to jump anyones case here. I also don't have a "click" even if you wanted to join, don't need my ass sucked by you or anyone, and also have no desire for you to get pissed off and leave. Get over the personal deal as it doesn't exist.
    [ June 28, 2003, 07:03 PM: Message edited by: Rexone ]

  9. #19
    Racing Ray
    Rexone:
    Now back to tech. I'd recommend a thermo unit with the exhaust bypass #160100.
    If excessive pressure in the block is an issue with a wide open valve there's ways to deal with that also.
    Rexone as stated by Hoss I think all I have ever seen is the valve in the water pick-up line. Can you supply more info on what you are talking about.

  10. #20
    Senior Member
    Join Date
    Jun 2009
    Posts
    10,871
    Ray, it is true that most jet boats, especially older ones are supplied with a gate valve on the engine water intake port out of the pump. And... it should be there for emergencies if you break a hose or something you can shut the water off so the boat doesn't sink.
    The problem arises when you start restricting incoming water flow to warm the temperature of the engine up (with the valve or any other method). You can get the engine temp up at running range but the majority of typical jet boats will then overheat at extended idle because of inadequate water flow at the reduced pressure the pump produces at idle and low speed. Open the valve, then you can't reach good operating temp running (most jets without thermo control run stone cold, like under 120 or less). It's a no win deal in most boats to restrict the incoming water. I've heard of exceptions but it's been rare.
    By using a thermostat assembly water flow is not reduced and idle temp as running temp is controlled by the opening and closing of the thermo. However it must be of proper design so water bypasses and flows into the exhaust when the thermo is closed. This eliminates overpressure and the burning of the exhaust manifolds, or headers in the case of headers. There are several variants of the plumbing that have been used with the thermostat housing. The following link shows the basic hose routing. LVJetboy has a diagram also that several on the forum says works well. It involves some valves to the headers etc. I'm sure he'd be happy to post it again here.
    Thermo diagram
    Thermo kits
    Additionally sometimes depending on the jet pump you will encounter an application that gets too much block pressure with the valve open (with or without the thermo unit installed). This is normally easily handled by installing a pressure relief bypass valve set at 15-20 lbs and / or dumping some additional water off depending on the exact setup. Bottom line is that it's better to find a way to dump excess pressure than to starve the engine for water at idle and overheat it. Hope that explains adequately.

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