Alpha one 5.0 cooling passages

Discussion in 'Sport Cruisers' started by AFD, Sep 9, 2018.

  1. AFD

    AFD Active Member

    Jul 29, 2012
    Boston Harbor/Falmouth Ma
    1997 Sundancer 290 The fat beam version
    Starboard 5.0 alpha 220HP
    Port 357 alpha 275hp
    4HP Yamaha for Dinghy
    I have an old raw water cooled 5.0 TKS with an alpha that just recently started to have an overheat issue under heavy load. When getting up on plane and maintaining a good speed under 4000rmps i have zero problems.
    when i start to push at or over 4,000 i see my temp gauge start to climb and this is a new issue as of a few weeks ago. we use the boat probably once or twice a week.

    first time it happened i thought that maybe i wrapped up some sea weed or a plastic bag or something because it immediately stopped and full speed runs just minutes later showed no issues. the next time i went out (a few days later) it started to climb and beep under heavy load. we went for a ride and kept temps just fine the rest of the time and when I got back to the dock and swapped my thermostat, i noticed that it had quite a bit of build up around the opening so i assumed that should solve the problem.

    went out yesterday and had zero problems reaching plane and temps looked good but after i started to push the rpms up, the temps started to climb again.

    i will get to the boat in 3 days (tuesday) and pull all the blue plugs poke the holes with my trusty old coat hanger that i leave in the bilge just for this purpose but i assume that there is either some scalling or some serious build up that will need to be addressed.

    Does anybody have any expreience with descaling an alpha driven engine? products to use?
    I assume i will have to put a big bucket under the drive and put a pump with the muffs on the drive and run the engine with some sort of acid...
    is there something else i should check?
    the water pumps are on their second year and i swap them every other year.
    the manifolds looked good at the begining of this year but i have already planed on swapping them over the winter/spring because they have served their time, 6 years now in saltwater.

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