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  1. #1
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    300 xs runs warmer water temp than the starboard.......

    2010 twin 300xs mercs, 140 hr each. I've noticed that the port runs a decent bit warmer water temp than the starboard. Gauge shows around 145 deg for the stbd and a bit over 160 for the port. no alarms. Water pressure is the same for each.
    I was thinking the thermostat might not be operating properly on the port, but a friend mentioned something about a poppet valve. Any words of advice, or just run it and leave it alone?

  2. #2
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    My starboard mota does seem to run a little higher at times , doesn't always run warmer .thinkin poppet valve also but I'm thinkin I'm picking stuff up that gets logged in poppet from time to time.TUNNEL T


    FINAL TOUCH DETAILING

  3. #3
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    swap gauges and senders see if they are the issue.
    Quartershot T-3R 15" 3.5L E-Tec 1.62 Sportmaster


  4. #4
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    the temp sender on 300xs monitors the temp of the compressor. at least mine does with analog temp gauges. the tan wire from sensor on the rear of compressor runs thru factory harness to gauge. there are 1 temp sensor in each cyl head that monitors each cyl head temp to control cold start up and will sound alarm horn and also put pcm in limp mode if either head overheats. my port motor also always run 5 to 10 degrees hotter than starboard. I drilled my pee hole fittings to about twice the original size after they seemed to plug up once or twice every outing where I was running in shallow areas to park. have not plugged since I drilled them and gauges always read about 5 degrees less than befoer drilling. if you follow pee hose backwards you will see it runs from pee fitting up to compressor outlet. the larger hole allows more water flow thru compressor. when pee fitting gets plugged it stops water flow thru compressor and compressor heats up fast.

  5. #5
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    Thanks for the info. I'll check the outlet to see, but I do remember seeing a nice strong stream coming from each engine. Ordered some gaskets.........guess I'll be eyeballing the tstats soon

  6. #6
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    I was just reading the diagnostic service manual for the 300xs........it says the tstats control water flow at and below 1200 rpms, but above that it's the poppet valve. I noticed that while running on plane the port engine will get 160-165 water temp, but when I go back down to idle and am in a no wake zone, the temp goes back to where it should be, around 140. The stream coming out is strong on both. Water pressure is same and adequate. I'll take a look at the tstats, poppet, and strainer this wk sometime after work

  7. #7
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    Poppets. Or lean. Even in 90* water i rarely get over 140 wot on 90+ Octane. Barely break 130 with stuff we dont mention. Run some seafoam through the gas. Might have some carbon blocking flow.

    If you have the smart thing check the water pressures. Or even a chunk of whatever in a pickup hole. 100 hour service is normally a impeller or to check it. Might have pressure but not volume
    Last edited by Motv18; 08-19-2014 at 10:53 PM.

  8. #8
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    Strainer had very little plugging. Poppet was unremarkable. Tstats also appeared normal. I put them in water and heated up. I know they are 130 F tstats but seemed to take til 150 for them to open, both at same time. Since they are in sync makes me doubt there is anything wrong w them. I noticed the vanes on the poppet fit pretty firmly into the receiver. Wonder if that's keeping the poppet from opening.

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