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  1. #1
    Seaman
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    Default Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Good Afternoon,

    I have received some fantastic advice in the past and cannot compliment this forum and the people enough.

    Allow me to, once again, come to the forum for advice.

    Vessel is a 1990 Wellcraft, twin Mercruise Inboard Engines (MEI) 454's, Borg-Warner V-Drive systems, etc.

    I changed out the impellers for both engines (removed the pumps from the engines, carefully replaced the impellers at home in the garage, reinstalled the pumps, etc).

    I found some crumbled rubber in the pumps from destroyed impeller blade(s) and cleaned everything as thoroughly as possible.

    When I start the engines, the port engine does not register any temperature increase.

    I've let it run for an equal period of time as the Starboard engine (which registers nice engine temp increase, etc) but no temperature indication at all on port side.

    Checked all the wiring, appears to be fine and in condition prior to the impeller changing.

    Strange that a temp sensor would quit and it would be very coincidental it would happen at the same time as this impeller change.

    I can switch sensors with the other engine to verify the sensor didn't go bad but it would be strange if this happened so suddenly AND associated with changing out the impeller.

    Any and all thoughts greatly appreciated.

    Thanks in advance,

    VerBoatin

  2. #2
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Have you physically checked the engine to see if it's actually getting hot? It may not show, but you could be burning things up.

    If there isn't any water in the cooling system, it's not going to register on the gauge.
    Don S.


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  3. #3
    Senior Chief Petty Officer wrench 3's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    If you weren't getting any water, I'd think you would be smelling burnt paint by now. More likely the thermostat is stuck open. Maybe there's a piece of impeller stuck in it? They usually make about 100'f with the thermostat stuck open, but might only reach that under load.
    "Growing old is mandatory. Growing up is optional."

  4. #4
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Quote Originally Posted by wrench 3 View Post
    If you weren't getting any water, I'd think you would be smelling burnt paint by now. .
    My point was, more of just asking if he even checked the engine instead of just looking at the gauge.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
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  5. #5
    Senior Chief Petty Officer wrench 3's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Sorry Don. Just an observation, not a criticism.
    "Growing old is mandatory. Growing up is optional."

  6. #6
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    No problem at all, just seen too many threads where people just won't leave the drivers seat to actually look/check things.
    Leave helm seat, jump in computer chair and type. Never look or check anything.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  7. #7
    Moderator achris's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    You also need to verify that the problem is the engine, not the gauge. Ground out the sender wire (at the engine end) to the engine block and check that the gauge 'pegs' hot. If it does, then start chasing an engine issue and not your tail with a dead gauge.

    It's a very quick and easy test and would be my very first check.

    Chris.....

  8. #8
    Senior Chief Petty Officer 04fxdwgi's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Curious, are your engines fresh water cooled? If so, sounds like a temp sender / gauge / grounding / thermostat stuck wide open issue.

    If raw water cooled, did you also do any work on the thermostat housings at the same time, like take them apart? If that did happen, possibly the bottom gasket w/ the rivets in it isn't making a good connection w/ the intake manifold.

    As Chris stated, grounding the sensor to see if the gauge pegs out is a good start. If it does peg, then either the ground or the sensor is no good. If it doesn't, then the gauge or wiring to it is kaput. Super easy to do and verify where to focus your attention.

    When running it, were you getting water thru the exhaust on the engine that didn't heat up? Was that checked?

    Old rule of thumb,,, After changing impeller, be sure water is available, start engine, go back and hold your hands on the exhaust risers and see if the risers quickly get hot.... On my '92 454, the risers will be warm (very front of riser will be almost same temp as water that is entering the engine from the pump), not hot. If only warm, then water is flowing thru them normally and water flow is good.

    Just reaching for straws here.

    Note: After all, this is a boat and all kinds of "strange things" can happen, but are usually quickly ID'd and explained, using decent troubleshooting techniques. The marine enviroment and corrosion, no matter how slight, will take it's toll causing gremlins to exist, usually in the form of crappy connections and especially bad grounds on the electrics.
    '92 Chaparral 2550 SX Sport
    454 BBC Mercruiser Bravo 1
    Tow with '04 F150 Larriat SuperCab 4x4 5.4 Triton
    US Coast Guard Aux.

  9. #9
    Seaman
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Thank you, one and all, for your advice and comments.

    You're right, at times people sit in the seat and scratch their head (or other stuff) and wonder why something isn't working.

    I did climb into the engine area, crawl all over the place with the engine running (I avoid this as I don't like being around the rotating pulley's and belts while standing on slippery surfaces) and it seemed like the engine was heating up as normal.

    I removed the radiator cap on the heat exchanger as well and the water was hot, etc.

    In reply to Chris' comment, it is a fresh water cooled system with the raw water going through the risers, etc.

    Having said this, I feel like a complete idiot for not looking at the exhaust outlets to see water coming out as I would normally see. I'm sure if it isn't pumping water, I've "fried" the brand new impeller (and I pray nothing else) that I installed and will need to replace it once again. Wow, back to motor head 101 for me, sheesh!!

    With all this in mind, I'm going to see if the water is circulating and if so, then I'm on to the possibility that the sending unit is bad or something along those lines. I will try the grounding technique to see if the gauge is working properly as well.

    OK, I'll check things over and report back to you on this...

    Thanks again...

  10. #10
    Moderator achris's Avatar
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    If you have closed cooling and it's full and the water's getting warm, you have a gauge/sender/ground problem. Do the check I suggested (ground the sender wire) and see if the gauge pegs. If it does, you have a sender/grounding problem. If it doesn't, you have a dead gauge...

    Chris......

  11. #11
    Seaman
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    Good Morning Chris,

    UPDATE: I ran the engines last night for about 15 minutes to verify much of what I read and remembered about the procedure.

    I still feel like an idiot but not so much now...

    Engines get warm but not "hot" per se. Good water flow in the heat exchangers (radiator) and equal amount of water coming out of both engine transom exhaust outlets indicating the impeller pumps are circulating water through the exhaust risers, etc.
    Starboard engine was starting to indicate warm on the guage but the Port engine remained at 0 on the guage. Both felt equally warm to the touch, if anything...the port engine felt a little cooler but that engine has the water heater connected so it takes a bit longer to heat up I would think.

    I suspect a sender problem but am going to follow all the excellent advice provided as to checking the gauge with a grounding of the tan wire and move on from there. I also plan to disconnect the gauge from the Starboard engine and hook up the Port engine (Starboard engine works fine so that can be my control for the test) via some test leads. If the Port guage works fine when connected to the Starboard engine and Starboard engine works fine when connected; the problem is narrowed down to the sending unit or perhaps a connection right there on the port side engine.

    Again, I cannot thank you enough for the guidance and help...

    I'll report back in when I find the problem as it may helpp someone else...

    Verboatin...

  12. #12
    Seaman
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    Default Re: Mercruiser (MEI) 454 Port Engine Temperature - Not Working after Impeller Change

    I am pleased to report that, once again, the wisdom of the kind experts on this site, have prevailed. The themostat was stuck open as described by "Wrench 3" and the situation is back to normal. Once I replaced the thermostat and ran the engine, everything worked perfectly. The hot water heater, which also works off the port engine (which had the bad thermostat) is again producing nice hot water when the engine is run and does not require the use of the 110 V from the genset, etc. THANK YOU MUCH, ONE AND ALL!!!

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