302 mercruiser overheating

Discussion in 'Powerboats' started by taseney, Aug 11, 2010.

  1. taseney
    Joined: Aug 2010
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    Location: south dakota,usa

    taseney Junior Member

    excessive exhaust pressure at the thermastat housing outlets. seems like any hose taken off you get a little bit of water and alot of exhaust. flipper broke off and came off of stern exhaust(not plugging exhaust). Is there a screen that can be restricting the exhaust pressure and forcing back thru riser.Stern pump replaced 3 years ago and boat has been ran 3 times since.Pump housing has hole drilled inside of it -is that for relief pressure or is there supopose to be something in that hole?
     
  2. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Three years is a long time for an impeller. Sounds like the engine is running dry. If the last impeller broke, there may be pieces of rubber clogging the water passages too.
     
  3. taseney
    Joined: Aug 2010
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    Location: south dakota,usa

    taseney Junior Member

    The impeller that was takin out 3 years ago was not broken(but was replaced). Took apart water pump on engine which looked fine other than a little rust. Took the impeller out again which looked alright.Put everything back together and hooked muffs up and disconnected the stern hose @ thermostat housing (also took thermostat out and filled with water), started engine for about a minute trying to see if there was circulation from engine water pump- NO CIRCULATION - Should there have been? Any thoughts on my problem?
     
  4. powerabout
    Joined: Nov 2007
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    Location: Melbourne/Singapore/Italy

    powerabout Senior Member

    I like to see what the hole in the water pump in the sterndrive is you are talking about?
    There is no pressure relief anywhere so if the exhaust elbows are rusted up and hence the water flow is very low the sterndrive pump will pump enough pressure to burst the hoses on the engine if they are old.
    You will certainly see them expand as you rev the engine.

    There is more water pressure than exhaust pressure so either there is no water or something has blocked your exhaust.
    If the flapper valves break they will break in half and will fit down and out the exhaust, this happens on most older engines and you would never know.

    Did you get a garden hose amount of water out of the hose that comes from the sterndrive and goes to the bottom of the thernostat housing?

    Forget the engine circ pump at this stage of troubleshooting, the water gets into the engine at that housing and also out but also is recirculated through it so depending where you are looking I doubt you would see anything
     
  5. taseney
    Joined: Aug 2010
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    Location: south dakota,usa

    taseney Junior Member

    Underneath the pump there is a plastic block that is part of the water chamber.In the plastic block there is a machined quarter inch hole leading into the water chamber from the outside of the plastic block. Is there suppose something in that hole? Took off the stern drive put in barrel of water and ran it with electric drill-water came out of water supply tube and you could see water was being forced out of hole in plastic block. Apparently losing water pressure thru hole in plastic block?
     
  6. powerabout
    Joined: Nov 2007
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    powerabout Senior Member

    Sounds like the pump base?
    Under the stainless plate.
    If it has a hole that runs sideways on one side ti sounds like an ancient pump base for a sterndrive or outboard from when they had a flushing attachment there.
    Its on the suction side and not the prssure side so I am suprised water came out?
    The gear housing had a corresponding hole with a plug and rubber seal to prevent it sucking air.
    You will need to seal that up.
    Time for a photo
     
  7. taseney
    Joined: Aug 2010
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    Location: south dakota,usa

    taseney Junior Member

    Thanks for feedbabck... Went down n looked at new part n came to that conclusion. Ended up tapping hole and putting bolt in it.(pretty sure it was on pressure side though)standing in boat looking at stern drive on left side.Just got everything put back together tonight ! Wont have a chance to get it out to lake til mid next week. Will post back letting know good or bad.
     

  8. taseney
    Joined: Aug 2010
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    Location: south dakota,usa

    taseney Junior Member

    Got the boat in water today... Appears problem is fixed !!! Ended up being a combination of problems. 1- plugged hole in ancient pump base. 2- pinched rubber boot in water supply (being a backyard mechanic i didnt know no better and slid water supply line up WITH drive putting back together and pinched or folded over rubber boot in process of doing so.) 3- Replaced impeller which im pretty sure old one was still alright- but replaced anyway.
    Anyways i really appreciate having a forum with active members willing to help!
    Ran boat for about 45 minutes on lake with temp ranging from 140 to 170. AWESOME !!! Time to bust out tube and get out and play a couple times before the South Dakota winters kicks in.
     
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