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

    3
    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

    512
    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

    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

    3
    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 Well-Known Member

    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

    512
    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

    364
    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
     
    Handsome Transom likes this.
  9. Cast away nick

    Cast away nick New Member

    16
    Aug 27, 2018
    1990 searay 230 2001 marine power 5.7 efi closed loop fresh water cooled.
    2001 marine power 5.7 efi fresh water cooled alpha 1 gen 1
    Did you ever find out what was causing the issue?
     
  10. Mini Yacht

    Mini Yacht New Member

    3
    May 17, 2018
    Connecticut, USA
    2002 Sea Ray 185 Sport - Bowrider
    4.3l Mercruiser 220hp - #0M300066
    Transom - #0M290514
    Alpha Gen II Drive - #0M406192
    Unfortunately I’ve been unable to solve the issue. So far, i’ve replace the theromastat, manifolds/risers, raw water pump and circulating pump. The only thing that made a difference was the circulating pump- it now runs at 205 instead of constistently climbing to 220.

    I’ve resorted to handing my vessel off to a very notable shop in my state. (ocean performance of Old Saybrook, CT). I dropped it off this weekend and they’ll be looking at it on Tuesday. I’ll definitely report back.
     
  11. Cast away nick

    Cast away nick New Member

    16
    Aug 27, 2018
    1990 searay 230 2001 marine power 5.7 efi closed loop fresh water cooled.
    2001 marine power 5.7 efi fresh water cooled alpha 1 gen 1
    I am haveing a similar problem. Please keep us updated and good luck.
     
  12. atrick

    atrick Member

    127
    Mar 4, 2017
    Penna
    1995 searay 290 Sundancer
    1990 21 maxum
    Twin 4.3 mercrusers with alpha one drives
    305 chevy with a alpha one drive
    On the alpha I gen II drives lower unit there is two cavities, one is where the water pump pulls the fresh water in from and the other is where the exhaust gas and hot water exits from. There is a 1/8" thick partition that separates them and it gets corroded away in time and will start pulling exhaust gas and hot water back into the motor. When you do the lower water pump you'll see what I'm talking about. Easy fix just rebuild the partition with JB weld for aluminium and should help with your problem. Happened on mine
     
  13. Cast away nick

    Cast away nick New Member

    16
    Aug 27, 2018
    1990 searay 230 2001 marine power 5.7 efi closed loop fresh water cooled.
    2001 marine power 5.7 efi fresh water cooled alpha 1 gen 1
    This is a gen 1
     
  14. atrick

    atrick Member

    127
    Mar 4, 2017
    Penna
    1995 searay 290 Sundancer
    1990 21 maxum
    Twin 4.3 mercrusers with alpha one drives
    305 chevy with a alpha one drive
    I think they're both the same, pull the pump housing off and the two cavities are there, no one notices them cause they never pull the housing off the lower unit, mine had a lot of corrosion and my mechanic told me about it or I would not have noticed it as the partition on mine was 3/4 of the way gone and it did help cool the engine down as the water pump impellor did look good.
     
  15. Cast away nick

    Cast away nick New Member

    16
    Aug 27, 2018
    1990 searay 230 2001 marine power 5.7 efi closed loop fresh water cooled.
    2001 marine power 5.7 efi fresh water cooled alpha 1 gen 1
    Thanks. I will be sure to look it over later.
     

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