Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

jlhoward39

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Jun 8, 2004
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* Merc 5.0 EFI with Alpha Drive – about 50hrs on it <br />* Winterized by Merc Authorized Mechanic in Nov 2003<br />* Memorial Day weekend...started for the first time, did not see the water pumping out of the back left (from the front of the engine) side of block.<br />* Ran engine for about 10mins, up to plane @4200rpm, before we noticed the issue.<br />* Shut down and towed back<br />* About a week later (due to work/schedule conflicts) Mechanic came to the boat from dealer, put plug in.<br />* I was not there, but my father was, when the mechanic started the engine it was missing, and as my father described it "hissing".<br />* My father checked the oil and it is still fresh and clean (no water as far as we can tell ).<br /><br />It is going into the shop on a trailer today. <br /><br />What damage could we have done? <br /><br />My guess is the head gasket is blown between the cylinders that are missing.<br /><br />Does the 2000 Merc 5.0 EFI have aluminum heads? Could a head be cracked?<br /><br />What else could it be? Fouled plugs from the fogger?<br /><br />The dealer is already saying "we don't know what happened to the boat between Nov and now... we would not have left that drain plug out." etc etc. So I am trying to get a quick education before they start work on the engine tomorrow... any input would be welcome.<br /><br />Thank you in advance…
 

Blk-n-Blu

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May 12, 2004
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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Jlh, I would guess your not talking about a freeze plug but rather a "block drain plug" if this is the case the motor could not have been properly winterized as the antifreeze that protects the block from freezing would have run out.Q. did you drain any antifreeze while de-winterizing,or run on the muffs before launching?<br />Did they store the boat or did you?From what you describe I would think no damage to the engine would result from a ten minute cruise.Is it possible they left the plug out when they drained the antifreeze? ymmv Just My $0.02
 

jlhoward39

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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Blk-n-Blu, thanks for your response.<br /><br />As far as which plug, I am not really sure as I am not real familar with an inboard Marine engine (yet). I had the Mechanic "winterize" my boat on the lift (over water). He left as "ready to run". <br /><br />When we started it, everything sounded and looked good on a cursory examination. We closed the hatch and went for a shake down run. About 5 to 10 mins into the run the engine sounds off, but ran smooth. It also did not have the "hot metal" smell I am familar with on auto engines overheating. <br /><br />We opened the engine hatch and found the bilge was full of water (up to the base of the engine). The water was hot, but I could still put my hand in it up to the elbow to lean over the engine with out getting burned.<br /><br />As far as what the mechanic did during the "winterize" proces, my understanding was:<br />1. Change oil in engine and filter<br />2. Fuel Stabilizer<br />3. Drain cooling system?!?<br />4. Fog System for setup.<br /><br />Again, when this was done, I was at work and my father watched over the process. ( The boat actually stays at his house on the lake. )
 

Blk-n-Blu

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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Jlh, It is some peoples choice to just drain the block and manifolds and keep them dry for the unused months,not my choice as rust will form quicker in the water passages if left dry (cast iron)If the mechanic didn't charge you for antifreeze it must be his choice of lay-up.The use of environmentally friendly antifreeze would be and is in my opinion the proper way to lay-up. Again I doubt very much any damage happened on that short run and that is my opinion also, your mileage may vary. be sure to keep an eye on your motor oil for a while and look for signs of water intrusion ( milky white oil ) Happy Boating
 

jlhoward39

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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Blk-n-Blu,<br /><br />Great info, and definitly something I will do going forward... I know the mechanic we used previously did use environmently safe anti-freeze. <br /><br />When I get home tonight I will review my receipt from this last winterization and ne mechanic to see if they charged me for antifreeze.<br /><br />I have been watching the oils, so far so good, no water in the oil. But since the problem was discovered and fixed, then engine has only been started once. That was when we heard the two cylinders (or more I was not there) missing and the "hissing". I guess it could be an intake valve too...<br /><br />Also, do you know if the 2000 Model Merc 5.0 EFI engine has aluminum heads on it?
 

burp

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Aug 3, 2002
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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Did the mechanic fog the cylinders by pulling the spark plugs and spraying fogging oil into the cylinders? Could the hissing sound be from loose spark plugs? But, that wouldn't be "ready to run" would it.....
 

jlhoward39

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Re: Merc 5.0 - Cooling Plug Out / Damaged Engine / Need Advice

Burp/Apprentice... <br /><br />Good point, as I mentioned I was not there when it was winterized. However, it ran smoothly without hissing when we first started it for the season. The system was definitly fogged as the typical blue cloud at startup was there...<br /><br />I will ask them to check that before they start to far down the head gasket trail.
 
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