Overheating Troubleshoot - 4.3L Mercruiser MPI

Discussion in 'General Maintenance/Repair Questions' started by Mini Yacht, May 17, 2018.

  1. Mini Yacht

    Mini Yacht New Member

    2
    May 17, 2018
    Connecticut, USA
    2002 Sea Ray 185 Sport - Bowrider
    4.3l Mercruiser 220hp - #0M300066
    Transom - #0M290514
    Alpha Gen II Drive - #0M406192
    Hey Guys,

    I recently purchased a 2002 Sea Ray 185 Sport two months ago and I'm trying to troubleshoot an overheating problem. I purchased the boat without knowing ANY maintenance history as the boat was owned by a Cobalt dealer as a trade-in.

    The engine is a 4.3L Mercuiser MPI (Serial #0M300066) with an Alpha 1 (Gen II) Drive (Serial #0M290514) and they're both original to the boat as far as I'm aware.

    I replaced the 160 degree thermostat with a new one this past weekend, and the boat wants to overheat at idle during the sea trial in 50 degree water. At idle, the boat approaches 220 sitting at the dock (before I turned it off and let it cool). However, when we took it out and opened the throttle up a bit, the temp got a little cooler. 190 degrees was the lowest temperature appearing at full throttle - about 42mph or so. The boat had no problem staying at 200 degrees under power, but approaches 220 at idle when sitting at the dock for 3-5 minutes.

    What do you you guys suspect? I'm thinking the lower unit's water pump may be to blame. If that's not the culprit, should I replace the circulating pump on the motor? And then do risers and manifolds? The boat was used in brackish waters for several years and then sat for about a year before I bought it. Any help is appreciated!

    I'm currently ordering the water pump as we speak, but I'm hoping that a DIY tutorial can also be provided if possible. I've never removed the lower unit from a vessel, and I'm a little bit apprehensive about the process after reading about it in my Mercruiser repair manuals.

    Thank you guys for your time, please respond back with any questions if I wasn't specific enough. I'm hoping to get on the water as soon as possible!

    -Kevin
     
    Last edited: May 18, 2018
  2. Espos4

    Espos4 Active Member

    409
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    Can you provide any water pressure readings?
    I don’t think a 2002 model year has that feature.

    If not, what about pulling off the raw water inlet hose and seeing how much water the pump is actually supplying at idle.

    You can remove the plugs from the underside of the exhaust manifold and see if they are packed with rust and debris.
     
  3. scoflaw

    scoflaw Well-Known Member SILVER Sponsor

    Aug 10, 2011
    cape cod mass
    1999 Powerquest legend 260 sx
    502 mpi Bravo 1
    Sounds like a solid plan, pump first
     
  4. Mini Yacht

    Mini Yacht New Member

    2
    May 17, 2018
    Connecticut, USA
    2002 Sea Ray 185 Sport - Bowrider
    4.3l Mercruiser 220hp - #0M300066
    Transom - #0M290514
    Alpha Gen II Drive - #0M406192
    Unfortunately there are no water pressure readings. I figured that while I'm waiting for the lower unit's water pump to arrive, I'll inspect the hoses for debris. When pulling off the raw water inlet hose, should I run the motor and check flow? Or should I see how much water is being supplied via pressure with the motor off? Or both?

    Thanks for the help guys. Other than this temperature issue, the engine hasn't skipped a beat and runs absolutely great. I'm going to check the engine oil again as well, but it looked clean after the original sea trial two months ago.
     
    Last edited: May 17, 2018
  5. Little Ducky

    Little Ducky Active Member

    936
    Jun 5, 2017
    Chattanooga TN/Dickson TN
    1998 SeaRay 290 Sundancer
    Twin EFI 5.0L w/Alpha 1 drives
    How about you have the dealer fix it as part of the sale?

    As you stated it was over heating at sea trial.
     
  6. Espos4

    Espos4 Active Member

    409
    Jan 1, 2017
    Long Island NY
    2007 240 Sundeck
    350 MAG Bravo 3 W/DTS
    You need to have the engine running to see any flow from the hose.
     
  7. BillK2632

    BillK2632 Well-Known Member SILVER Sponsor

    Jun 25, 2009
    Lake Norman, NC
    1999 185 Bowrider,
    Mercruiser 4.3, Alpha I
    I think I would just start with the water pump, you don't know know when it was last changed, the service interval is every 2-3yrs on a Alpha Gen II. It's cheap and easy to replace, then you are starting from a known good point. You could have other issues with clogged risers etc, but if the water pump isn't working right, it's just not going to cool properly.

    Circulating pump on motor lasts a long time, telltale sign of a failure is a leak from the weep hole on the front of the pump.
     
  8. Happy Dayz

    Happy Dayz Active Member

    320
    Jun 26, 2017
    Sarasota, FL
    '06 260 Sundancer, 6.2, BIII, Kohler 5kw
    79' classic Kona Family Cruiser jet boat..
    6.2 w/ BIII, 502 w/ Berkekley
    dont waste a bunch of money replacing parts...

    when i got mine.. slowly overheated

    after both pumps replaced, thermohousing, etc.. 3rd time removing all hoses found piece of old impeller... pump had a new one in it but prevowner servicing didnt go through system... runs great now

    check impeller 1st
    start at hose from pump, look through each section... i bet you find a broken piece blockage
     

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