Overheated - Now starts hard, runs rough

Discussion in 'Powerboats' started by Boomvang, Jun 26, 2009.

  1. Boomvang
    Joined: Jun 2009
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    Location: Michigan

    Boomvang Junior Member

    Well I guess I get to join the dummy club. My 1984 351 PCM (no elec ignition) got overheated the other day. When I realized it I idled back to the dock. I found a leak in the hose to the water pump (hence no water leaking when I checked).

    The motor didn't seize, it ran fine idling back to the dock. When I got home and it cooled down, I started it briefly, seemed ok. The next day I changed all my hoses, new impeller (old one was destroyed). Now the motor is very difficult to start. Cranks like crazy, acts like it wants to start but can't "catch". Then when it does start, it runs very rough for a minute or two and then dies (like it's not getting enough gas).

    One oddity - took off the distributor cap, cleaned up points and rotor, put cap back on and it wouldn't even TRY to start. Took the cap off, confirmed that I had put the rotor back on (I had), put the cap back on and it immediately changed back to the earlier symptoms of (hard starting, stalling). Seems to indicate that the distributor is somehow involved?

    Sorry for such a long post. Thanks in advance for help.

    Steve
     
  2. pistnbroke
    Joined: Jan 2009
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    pistnbroke I try

    Compression test to see if you have buggered the bores

    Clearly you did not seat the dissy cap properly .....forget that go with what goes wrong when you over heat it ...????
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Sounds like a head gasket(s).
     
  4. Boomvang
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    Boomvang Junior Member

    I was thinking (fearing) head gasket as well. I drained the oil today and was happy to see...just oil, no water.

    Am I correct in thinking that rules out head gasket?
     
  5. Frosty

    Frosty Previous Member

    No --the head gasket could have blown into the water, actually could have been the reason for overheating. Fit 2 new gaskets, plugs ,oil and thermostat.
     
  6. pistnbroke
    Joined: Jan 2009
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    pistnbroke I try

    may have blown between cylinders which is common .. or between cylinder and water gallery then the pressure stops the water circulating ....only water in oil if the leak is between oil and water gallery ..at least you have not buggered the bearings !!!

    get the head off ...
     
  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    Diagnose properly first, before you start ordering parts. There are several test you can do, try a leak down test first.
     
  8. Frosty

    Frosty Previous Member

    A leakdown test will show that, but thats expensive equipment.

    A top end gaskets set is what 20 dollars and 4 hours work?
     
  9. CDK
    Joined: Aug 2007
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    CDK retired engineer

    A blazing hot engine and just a few splashes of cold water from a damaged pump, that's a recipe for expensive trouble. Pistnbroke's gasket, blown between the middle cylinders is very likely, so is Frosty's leak to the cooling circuit.

    But there may also be cracks in the head itself, where cold water hit the metal. And the risers will have suffered, together with the hoses attached to it.
    The engine is 25 years old: this may be the moment for a complete overhaul.
     
  10. gonzo
    Joined: Aug 2002
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    gonzo Senior Member

    You can buy a compression tester for about 25 buck. They are not professional grade but will do. It would seem odd that the head gaskets on both sides are so bad that it won't even fire. Check the sparkplugs. Sometimes in an overheat the oil thins out and fouls the plugs. Changins parts without troubleshooting first is stupid. You end up not knowing what caused the problem.
     
  11. Frosty

    Frosty Previous Member

    He did'nt say a compression tester he said a leak down tester.

    Its just 2 head gaskets. I could have done it by now.

    It does run Gonzo but runs rough.
     
  12. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A compression tester will work too. Clearly the poster is in over his head or would have sorted out the symptoms by now.
     
  13. Frosty

    Frosty Previous Member

    A compression tester tells you what your compressions are . A leak down test puts in air from a compressor and gives you a % reading of leakage,then if you listen to exhaust, intake, crank case or radiator you can see where its leaking to. Totally different machine one is expensive the other is not.
     
  14. gonzo
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    gonzo Senior Member

    A leak down tester at Harbor Freight is selling for about $70.00. That is not so expensive. I don't think that you can see where it leaks in a gasket with a leak down tester. The air will go from the combustion chamber into the engine.
    The engine is not running, it only cranks
     

  15. mydauphin
    Joined: Apr 2007
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    mydauphin Senior Member

    Pull the plugs see if it turn over easily. But chances are your are going to have to pull heads... You may have damaged bearings...
     
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