Engine overheats after severe heeling

[tafelice]

Okay, tell me if you know what is doing this and how to prevent it.  I have an S2 30' with a Yanmar 2GM raw water cooled.  This problem has happened 3 times.  Once while undersail on a reach, port tack, we hardend up around a marker and initially heeled over quite a bit.  Within about 20 seconds the engine alarm screams.  We shut it down.  It starts but is indicating overheating on the restarts.  We sail for another 40 minutes, start up and problem is gone.  Next incident, we are motor sailing in the Gulf and we see two large steep waves coming and we get heeled over quite severly, and 20 seconds later same as above.  This time waiting 40 minutes does not clear up the problem.  But taking every water hose off and reattaching does.  Last time we were lifted by a large wave from astern, same problem, this time we take off just the hose that goes into the exhaust, run the engine till water comes out of it.  Shut down, reattach and restart.  Okay, what is going on here?  I believe it is some form of air lock but this should not happen and I need to fix it because I don't want to sail like this in fear that my motor will overheat after a rough wave or heeling.  Has anyone else experienced this or heard of something similar?

Tom

[AdriftAtSea]

Tafelice-

Does it only happen on a port tack?  Where is the raw water through-hull located?  Where is the raw water strainer mounted in relation to the water pump water inlet and the raw water through-hull?  It definitely sounds like you've got the cooling system airlocking. 

A couple things I would suggest.

First, mount the raw water strainer as low as possible, and as close to centerline as possible.  This will help keep it under the water line at all angles of heel, reducing the risk of air locking, provided the through hull stays in the water. 

Second, buy a Globe brand impeller, which can tolerate running dry far better than a standard impeller, due to the different polymer they use in their construction.  Have you inspected your water pump impeller and cooling system for any blockages—broken impeller blades are often a good source of cooling system blockages.

Third, check the actual through hull and seacock and make sure they're not fouled in any way.  Barnacles, kelp, fish (yes, don't laugh small fish can get stuck in the seacock) or something else could be impeding the water flow.

Fourth, is the raw water for the engine cooling system through hull used for anything else, like the head saltwater feed??? In a boat I was just working on, it had a similiar problem that was caused by the pump pulling air down into the cooling system because the owner had put a "T" into the raw water cooling line to feed a new head he had installed. 

Let me know what you find out.

[tafelice]

No, re port tack.  I actually found that one incident to be the strangest because the through hull is on the starboard side.  However, those who have looked at it say that the through hull is as close to the centerline as possible.  The through hull is only a foot forward of where the prop shaft exits the hull, so I thougth it was too far aft but this spot is still more than seven feet from the stern.

No blockages that any could notice.  When the first line is disconnected at the water pump the sea cock is putting out a stream of 8-10" of water.  This intake is NOT being used for anything else.  Blockages you mention would not have anything to do with this heeling problem but would create problems at other times.

When I took off the water pump (on my boat you actually have to take off the entire water pump to change the impeller, you can't just unscrew the backing plate) the backing plate was scored pretty bad.  I reversed the backing plate and cannot tell if that helped beause I haven't had a bad heeling condition since then.

[AdriftAtSea]

Hmmm... I don't see why it would air lock if the intake is on the starboard side, basically on the bottom of the boat.  If the through hull is clear, under the deepest part of the boat, and not shared, the problem has to be crud inside the cooling system itself. 

Have you tried flushing the cooling system to see if there are any blockages in the system, like broken off impeller blades? 

The water pump sounds like a bastage to service.  If I were you, I'd replace the water pump at the next convenient time with one that doesn't have to be removed to service the impeller.  What a stupid design.... they should make the engineers work on the darn engines they design for a month... you'd see much more intelligent design in a hurry then. 

Also, was the scoring on the plate is a semi-circular shape?? That would indicate that some debris was caught in the impeller and may have made it into the heat exchanger... and that could be causing the intermittent blockage. Get a Globe impeller or two as spares... they're pretty reasonably priced insurance.

[tafelice]

okay, if I have a blockage why does the air lock occur only at heeling? 

I guess you could say it was semi circular, it was just less than circular.

[AdriftAtSea]

If the blockage is caused by a piece of debris in the heat exchanger, it could well be that it is wedged and depending on the angle of heel, either not blocking or blocking the exchanger's passageways.

The semi-circular scoring leads me to believe that an impeller probably self-destructed in the water pump at some time in the past, and the PO never hunted down all the pieces at the time it happened.