Diesel endurance

[jnj]

Recently started our 18hp Yanmar without opening the seacock. It ran for at least 10 minutes before the TEMP light came on and the alarm sounded. I quickly had the seacock opened and the engine cooled down. There is a water heater that works off the secondary cooling system (fresh water w/antifreeze) and it was empty when I tried releasing hot water from the galley faucet. Since then I took the boat out three times and I noticed on the last run a very slight film of oil or fuel coming from the exhaust discharge pipe. I don't recall seeing it before each time I ran the engine but its disconcerting now. The raw water intake impeller/pump seems to be performing well.
Have I done any real damage and where might it be?

[capngregg]

I would recommend disassembling the raw water pump and inspecting the impeller at a minimum. It's never benficial to overtemp an engine of any kind but it's unlikely you sustained any substantial damage to the engine itself. (other than possibly shortening the life of the raw water pump impeller)

The oil film that you're seeing may have always been there but you probably didn't have any reason to be as concerned prior to the overtemp incident. How many hours are on the engine? Have you had the injectors cleaned lately? Has the engine been operated under cruise power lately or just alot of idling around? All of these things may be the origin of the oil film. Diesels never run completely "clean" so I would monitor the engine performance and oil comsumption ( you should be keeping a log anyway) for a few months to determine if the engine may be deteriorating.

As for the water heater issue, I'm not sure what you're asking.

[jrd22]

I would agree with Greg above, you probably didn't do any serious damage. I would change the impeller in the raw water pump, it could have cracked the vanes if it got hot, better safe than sorry. Monitor your antifreeze level to make sure you didn't develop any leaks, when it gets that hot it builds up a lot of pressure in the system. I hang the ignition key on the engine water thru hull so I can't forget to open it.

John

[Rockter]

A motor with a heat exchanger will not like it, but it sounds like you escaped punishment. Don't restore the coolant quickly like that, let the motor cool first or the very hot exhaust elbow suddenly gets cold water splashed all over the inside of it.


Never do that on a raw water cooled motor.
That lesson has been learned so often.
Let the motor cool first.
A raw water motor will very likely crack the cast iron somewhere if you allow cold water in there and the motor is very hot.
Let is cool off, like an angry woman that you have to talk to again.

End of sermon.

[sailboy21]

My exhaust elbow clogged up about 200 yards from my slip. I noticed a distinct change in the sound of the exhaust, as well as the missing splash of cooling water. As I was motoring up the slipway I really had no choice but to press on. The engine temperature remained constant, never got above 170. This was with about 5 minutes w/total loss of cooling water. The exhaust hose from the elbow to the water lift on the other hand was completely destroyed. The exterior looked okay, but the inside was bubbled and melted. The plastic water lift seemed to be just fine and is still in service today, as well as all of the downstream exhaust hose.
So, along with a new impeller, I would strongly recommend replacing, or at least inspecting the exhaust hose.

[jnj]

Thank you all for the encouraging remarks about not causing any serious damage. I have had car engines overheat back in the 60's and was always careful to avoid a sudden cool down. The reason I introduced cold water through the seacock when I did was because I was maneuvering through a tight, shallow channel with lots of weekend traffic and I needed to maintain power and not drift.
That is good advice about the impeller check: I believe I'll just replace it on principle. I have a spare impeller and that's what I'll do on my next trip to the boat.
More than anything I'm worried about the heat exchanger. I was thinking that if there's a leak from the fresh water coolant chamber into the exhaust then it probably is coming from a ruptured tube in the exchanger. I'm going to drain the remaining coolant and liquid from the fresh water section and replace it with bright green-gold antifreeze and see if there's any discharge. There is no steam in the exhaust so I'm ruling out any water leaking from a crack in the jacket into the cylinders.

As for the question of time on the engine: the boat is 20yrs old with generally soft weekend use and the engine is rarely run except to travel to or return from the open water about a mile away.