Engine Temps

Can anyone tell me what are appropriate operating temps for a FWC 5.0 Merc? I have one engine that is at 140 at all speeds but my port engine will waver around 160/165/170 and fluctuate regardless of speed. I originally thougtht that I had different t-stats, but what would explain the temp fluctuating.

I just got the boat last weekend....so I am not sure where I should be.

2001 310 Fiesta Vee

T-5.0 FWC Mercs w/ B2


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    Dream_InnDream_Inn Member, Moderator Posts: 7,594 mod

    You should be using a 160F thermostat for FWC.  This would mean both engines should be running around the 170 mark. I'd say one engine has the wrong thermostat in it.

    Dream 'Inn III -- 2008 400 Express

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    212rowboat212rowboat Member Posts: 2,591 ✭✭✭✭✭
    my take, for what it's worth:

    175* and dead nuts solid w/ a 160* 'stat...

    the 140* indicates a 'stat that is failed, as most fail in the open position...

    the fluctuations would concern me.. how much swing are we talking about, and how abruptly? Wide swings during acceleration and deceleration indicate blown head gaskets (worst case), a bad circulation pump (middlin), or a clogged passage/or water supply (best case)...

    of course, it could just be your gauges... faria?

    'stats are really simple to swap- and being new to you I'd likely swap them along with a full service.. gives you a basis to work from... circulation pumps aren't that bad a job to do or have done- can be a little time consuming is all, likely an hour each or so...

    again, though, with a 160* stat, you should be holding dead nuts no hotter or cooler than 175*/170* once operating temperature has been established...
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    TikiHut2TikiHut2 Member Posts: 1,431 ✭✭✭✭✭
    I'd change that one theromostat because it's so simple, and get yourself a non-contact Infrared heat gauge/thermometer to double check those problematic Faria gauges directly at the engine....and everything else that inquiring minds need to check for heat. Often on sale at Harbor Freight for $30. Good luck, Mike
    2004 FV270, 300hp 5.7 350mag MPI Merc 305hrs, 2:20 Bravo3 OD w.22p props, 12v Lenco tabs, Kohler 5kw genset, A/C, etc.etc...
    Regular weekender, Trailer stored indoors, M/V TikiHut, Sarasota, Fl
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    FlyingBlind310FlyingBlind310 Member Posts: 49 ✭✭

    Thanks for the advice..IR gun is on order....

    I don't think (hope?) that the port engine has a blown head gasket as I had a compression test performed w/ good pressure.

    Since the boat is new to me, I think I am going to run the engines at the dock this weekend to see what my true running temps are w/ the temp gun. Knowing I should be at 170, I want to see where the port engine stays....

    2001 310 Fiesta Vee

    T-5.0 FWC Mercs w/ B2

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