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Thread: Underheating Problem, Maybe?

  1. #21
    LVjetboy
    Mandelon,
    "What temp should I be running?..."
    Not as clear as some may think. Unless of course you're predisposed to accepting whatever expert's post you want to believe.
    "I'm surprised the existing thermostat have issues at 120 hours"
    I ran w/o a thermostat (INLET valve controlling both temp and pressure) for two years on the Dragn, then a Rex thermostat kit (and valve on INLET to control pressure) for about 9 years after. This on a 400-425 hp engine. After a total of eleven years, the engine still ran strong to 5k (with many a NOS burst to 5.5k) So no family cruiser. On tear-down my builder said little wear.
    I know splitting hairs. That's why you'll see many different opinions, 'cause more than one solution works just fine. But if you're looking for a pro with the simple answer, well then skip on by this post.
    Me? I'm always interested in the very best solution for an application, and as hp goes up, so does the sensitivity to the "right solution" Not always posted here.
    So I continue to question.
    Floored, I understand the temperature vs. clearance issue you mention. My point, do you really know what that temperature is? I'm guessing most mfg's are keyed to car blocks. And what little block wear info there is for car blocks. Even if Mandelon's block or most jetter's blocks are bored and honed with hot water circulation? I'm guessing probably not.
    But even if? How does the mean metal temperature and resulting cylinder shape and piston clearance match conditions at the lake? A big unknown, especially considering oil temperature (not water temperature) may be the driver. So the obvious question is, does "low" coolant temperature and "high" oil temperature result in lower or higher mean block temperature? Even if someone could define "low" coolant temperature. Nobody I know has the answer...
    Besides clearances, there's the issue of contaminate burn-off and wear. For that you need "reasonable" oil temperature. But I'm thinking "reasonable" oil temperature, if well-defined, may be driven from something other than "normal" coolant temperature for a car than a boat? In other words, if 190 is reasonable oil temperature, does that take 120 or 160 degree coolant exit temperature to get that 190 oil temperature in a boat?
    Then there's the question of cylinder compression ratio and engine timing and how they're influenced by head temperature and cooling flow.
    Bottom line? We can all post what we think about ideal coolant exit temperature, or our experiences with valves and thermostats. I can tell you a Rex thermostat adjusted to 190 degree idle temp and a valve regulated inlet pressure worked just fine for me.
    In the end, there's still a lot to be known about what is the best for each application. That's why I ask those questions in my post above.
    jer
    [ June 29, 2003, 01:55 AM: Message edited by: LVjetboy ]

  2. #22
    Floored
    Jer,, how close is your engine to being done? Where are the pics? Boat engines are a different breed of engine than any other. Drag engines are loaded quite differently and for a much shorter time than a boat engine. When you think about it the stresses on a boat eng are phenominal(I know big word)and they are constantly loaded and unloaded just cruising across a lake. Closest I can think of is running Baja in a 4wd truck, minus the dust. Most of my experience machining was drags,some score and a little indy. Got to see some funky experiments, some worked, some didn't. If you learn from it then okiedokie. I did learn to ask lots of questions and if 10 answers were one way and 2 the other, then maybe the 10 were right. If any of us knew it all we wouldn't be on the boards, we'd be busy and filthy rich. do they make a Merlin flathead Rambler 6? idea

  3. #23
    DansBlown73Nordic
    WoW am I glad I have V-Drives. They run 160-180 all the time. By the sounds of the Jet thing. You either have too much pressure, too much temp at idle or smile_sp smile_sp
    idea Maybe just covert them all to V-Drives.....lol wink
    [ June 29, 2003, 08:20 AM: Message edited by: Dans66Stevens ]

  4. #24
    Racing Ray
    Dan funny you mentioned that. I just told my son last night on my flat bottom the same thing 160 all day long. My sons jet however is plumbed like Rexone said of older jetboats. He does have a ball valve between the jet and motor with a gate valve on the return. Same problem as others with this set-up. 120 on the lake and watching every moment when idling.
    It is a problem for him as to get to the party spot on our local lake you need to cruise about 2 miles in a no wake zone to Sandy Beach. I was talking to him last night and I think we will change it to the set-up explained by Rexone. That is about how the factory did it on my Mercrusier unit.

  5. #25
    GofastRacer
    Mine runs 165-170 idling and cruising all day, when I run laps, it may get up to 190 max, and that's running 7500!..

  6. #26
    LVjetboy
    Floored, my engine done? Maybe the end of July. Just in time for TP3/C3B? The “10 one way, 2 the other” seems reasonable, unless those 10 read these forums and believe what they read Urban legend becomes accepted fact. The other 2? Maybe they go out, test or research then learn the true answer.
    Dan, convert to a V or just run a water pump like a V? I think the problem with tapping the jet pump is there's too wide a pressure range from idle to full throttle. Not that the jet tap can't work, it’s worked fine for me so far, but it may not be ideal for cooling.
    As for the T-Rex and cooling temperatures? I set mine to idle at 190, then cruised about 160-170. No adjusting hassles with a thermostat. Is this the best coolant temperature or best setup? Don’t know for sure. I did measure my oil temperature on a hot day once...265+ near full throttle cruise. Pretty hot considering my coolant temperature. Jet boat cooling is no new topic here, we’ve talked valves types, line sizes, pressure relief, air pockets, reverse cooling...on and on. I guess I’m just trying to add a different angle...maybe get feedback on some of the key questions that go unanswered. Like how do we really know 120 water temp is bad for single pass cooling if oil temp is in a good range?

    jer
    [ June 29, 2003, 04:51 PM: Message edited by: LVjetboy ]

  7. #27
    HBjet
    Well, here is my 2 cents!
    I run a water pressure regulator, and I believe LV is going to be running one as well. At idle, the block is at 10psi, at throttle, around 18psi, and my water temp at throttle is 110-115 and once I come off plain, it jumps to about 130-135.
    Motor runs perfect!
    HBjet
    [ June 29, 2003, 05:46 PM: Message edited by: HBjet ]

  8. #28
    LVjetboy
    Rio, so you got something technical to add or just BS? Don't hold back now, doesn't fit your image.
    jer
    [ June 29, 2003, 11:53 PM: Message edited by: LVjetboy ]

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