Mercruiser 350 over heating at hign RPM

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  • PartsManPartsMan Member Posts: 246 ✭✭✭
    Yesterday I removed the sensor and cleaned it, but didn't seem to be too dirty. I still read 0.0 for water pressure so either the sensor is bad or the monitor is not reading the sensor.



    I did find a bunch of zebra mussel shells in my strainer. I cleaned and will take for a ride today. Hope this was my problem.


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  • PartsManPartsMan Member Posts: 246 ✭✭✭
    @Pam - Ya I did the hose this spring. By the way, that has to be the worst boat repair. I would recommend everyone to pay someone to do it.
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  • MarkBMarkB Member Posts: 3,976 ✭✭✭✭✭
    Do you run a single or twins? If you have twins can you take the sensor from the other engine and swap it with the problem engine?

    Boat Name: King Kong

    "Boat + Water = Fun"

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  • PartsManPartsMan Member Posts: 246 ✭✭✭

    @MarkB - Single

    Called Mercruiser and they said not all models of the mercmonitor read water pressure. Took the boat out and once again the boat went into guardian mode at 170*. At this point I think I have to have the motor scanned to get the error code.

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  • rasburyrasbury Member Posts: 8,410 ✭✭✭✭✭
    yep, at some point, we have to all bow to Mecca
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  • Black_DiamondBlack_Diamond Member Posts: 5,439 ✭✭✭✭✭
    I had this problem and it was the raw water hose coming in from the drive. It was twisted/kinked from improper installation. 

    Past owner of a 2003 342FV
    PC BYC, Holland, MI
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  • LaReaLaRea Member, Moderator Posts: 7,756 mod
    You might have to get it scanned while you are underway, when the alarm is actually happening.  Not all alarm codes get stored.  
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  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    I use the hand held Lazer temp thing all the time.100ish on manifolds and 80 ish on risers.also sending unit 170.gives me comfort 
    Part of my per trip.
    2005 Rinker FV342  Pawcatuck river,Ct
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  • PartsManPartsMan Member Posts: 246 ✭✭✭
    Well hope this answers my problems. Had the boat scanned for codes this morning. The Sea Temp Sensor is bad. Ordered a new temp sensor and water pressure sensor (bad too) be here tomorrow 
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  • reneechris14reneechris14 Member Posts: 3,134 ✭✭✭✭✭
    I hope that works good luck 
    2005 Rinker FV342  Pawcatuck river,Ct
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  • Dream_InnDream_Inn Member, Moderator Posts: 7,663 mod
    Sounds like you may have finally got it!!  can't wait to hear results!

    Dream 'Inn III -- 2008 400 Express

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  • raybo3raybo3 Administrator Posts: 5,503 admin
    Good luck PartsMan hope it works out for you....
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
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  • MarkBMarkB Member Posts: 3,976 ✭✭✭✭✭
    Partsman, that's what I thought it would be!

    Boat Name: King Kong

    "Boat + Water = Fun"

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  • howardramshowardrams Member Posts: 223 ✭✭✭
    Did you find someone local to do the scan or trailer the boat to them?  I noticed Time Out was away from the dock on Sat.
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  • howardramshowardrams Member Posts: 223 ✭✭✭
    Oh yeah, and whats with those CAVS???
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  • Dream_InnDream_Inn Member, Moderator Posts: 7,663 mod
    Oh man, those CAVs are driving me crazy!!  Just hearing that they don't even have a chance, and then blowing it right now!  Ugggh!  & I don't really even watch NBA.  But I am a die hard Cleveland fan.

    Dream 'Inn III -- 2008 400 Express

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  • raybo3raybo3 Administrator Posts: 5,503 admin
    LeBron is a locker room cancer. Great player but bad for a team. Remember there is no I in team. BTW I am not an NBA fan so I am going on what the talk shows say..........LMFAO 
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
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  • PartsManPartsMan Member Posts: 246 ✭✭✭
    @howardrams - Just went to the beach on Sat. as long as I don't get on plane everything is fine.

    Watch the ESPN 30 for 30 show "Believeland" and that pretty much wraps this Cavs season up. Another disappointing Cleveland sports team. Looks like it's now the Indians turn to let us down. They are putting together a strong team and season.
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  • raybo3raybo3 Administrator Posts: 5,503 admin
    PartsMan Francona got a screw job with the Red Sox. I think he is a very good manager. I really liked him here. 
    2002 342 Fiesta Vee PC Point Of Pines YC Revere MA. popyc.org     raybo3@live.com
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  • cduffycduffy Member Posts: 11 ✭

    PartsMan What ended up being the fix for the overheating?  I am started having this problem mid last summer and it got worse thru the end of the summer. 


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  • randy56randy56 Member Posts: 4,083 ✭✭✭✭✭
    PartsMan said:
    Well hope this answers my problems. Had the boat scanned for codes this morning. The Sea Temp Sensor is bad. Ordered a new temp sensor and water pressure sensor (bad too) be here tomorrow 

    Boat Name : 

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  • rasburyrasbury Member Posts: 8,410 ✭✭✭✭✭
    Was fixes!
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  • rasburyrasbury Member Posts: 8,410 ✭✭✭✭✭
    Easy...
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  • Michael TMichael T Member Posts: 7,227 ✭✭✭✭✭
    High engine temps can easily be caused by a jammed/burnt exhaust flapper or a water inlet hose that has weakened and collapses when the sea pump draws on it. A twisted/crimped sea water inlet hose will do that too.
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  • russellhrussellh Member Posts: 155 ✭✭
    Without a doubt new manifolds will improve your running temp. I've had new manifolds and risers on two engines on two different boats in the past 4 years and each time reduced the temp down to idle 160f and cruising at 175f. You can soon tell, open the hatch when it goes into limp mode and feel the manifolds with your hands. If too hot to touch then there too hot, if not the problem lays elsewhere. I've not had a heating problem since I replaced. 
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  • russellhrussellh Member Posts: 155 ✭✭
    The simple hand touch test is best!
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  • cduffycduffy Member Posts: 11 ✭

    I am at a new lake, so I am using a new mechanic. He came recommended from a couple different friends.  So here's what he is saying.  The water pressure was high so he is saying it is on the output side.  He tested the pressure at different areas and thinks the heat exchanger has some blockage.  Says he checked the risers and manifolds and thinks they are fine.  Does this sound like something that a new heat exchanger will be the fix? 


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  • cduffycduffy Member Posts: 11 ✭

    Randy, I saw the comment about the Sea Temp Sensor, but next saw a confirmation that was the fix.


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  • randy56randy56 Member Posts: 4,083 ✭✭✭✭✭
    Could be heat exchanger, or flapper. What year is the Rinker?
    Boat Name : 

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  • PartsManPartsMan Member Posts: 246 ✭✭✭
    My issued was clogged elbows. It was a fluke finding the problem. I took the elbows off to inspect the manifolds. I was cleaning the elbows up and blow some air in the hole and corrosion came out. Cleaned up as best I could with a hanger, air and water. The boat ran cooler but still not right. I replaced the elbows this spring and the boat is running prefect. 

    Check you flapper that an easy job, mine where fried.
    Heat exchangers only last 10-12 years. Pull the exiting hose and check for antifreeze. If theres antifreeze the heat exchangers is bad. 
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