Air lock?

[LARRY VALENTINE]

A few weeks ago I brought my HAT 53 ED back from bottom paint and a new Groko BRonze strainer mechanism after making sure all of the thru hull valves worked properly. Twenty minutes later I arrived at my dock after a low speed trip to find a heat alarm going off but with normal temp guage readings. Today while running the the 6v92TA engines I noticed almost no water coming out of the Port exhaust at slow or 2500 Rpms as
compared with the starboard engine.
The new impellers were installed 18 mo
nths ago with rebuilt pumps. The boat has had

no use inbetween. I suspect an air lock of the port engine. How do I make sure and how do I correct this???

 

[rob71]

It is very possible the impeller shredded if the system did not have water to it upon startup
That happened to me after a haul out and I did not "burp" the strainer to make sure no air was in the system.
Capt. Rob

 

[Pascal]

I had the same thing happen a few years back after launching the boat I run (cat 3412Es). Cat mechanic was in the ER for a sea trial after 3000hr service so I ASSumed he checked for water flow after he started. 15 mins later he comes up and tells me the stbd engine was airlocked Of course by that time the impeller was toast...yet because we where idling out the coolant temp was normal

I always check for flow after start, both gennys and mains. If starting from the ER you can just put your hand on the pump cover to make sure it s cool. They ll get hot siting seconds if no flow

I ve also lost prime a couple of times on a start for no apparent reason. Usually popping up a flush or zinc fitting down stream of the water pump was all it took to release the air lock. Not sure wher that would be in your case

I also pop the pump cover to check the impeller it may have been damaged

Again checking for flow after start is always a good idea, on our hatts it only takes a second to walk aft.

 

[SEVEN]

The key thing you said that took my mind right to the impeller was the boat sat idol and wasn't used. The impellers dry out and get brittle without use. Check there first. Good luck.

 

[LARRY VALENTINE]

Thanks for the replies. My mechanic took the cover off the raw water pump and indeed the impeller was shredded

with the impeller bits blocking the outflow from the pump..A new impeller was installed, the pieces removed and then

the motor started. The water then appeared at the exhaust of the involved engine, but the volume did not seem appropriate when compared with the other engine at the same RPM.. We then went into the heat exchanger and found large calcium deposits. We extracted as much as we could from the inflow and effluent sides, then looked at the exhausts. Again there was more wa
ter exhausting the other engine. The exchange tubes are now in the shop undergoing an acid bath.
I hope to be cruising the Chesapeake on the 4th but I am not sure what year!

 

[SEVEN]

Great to hear. Lucky it wasn't something bigger. Happy 4th cruising.

 

[MikeP]

There could be debris clogging the showehead holes. I have pulled what looks like small rocks(!) out of shower heads. Also, mufflers can collapse internally and clog. Is the sound volume and "quality" about the same from both exhausts at the same RPM? If not, that might indicate a muffler problem.

 

[bobk]

Thanks for the replies. My mechanic took the cover off the raw water pump and indeed the impeller was shredded

with the impeller bits blocking the outflow from the pump..A new impeller was installed, the pieces removed and then

the motor started. The water then appeared at the exhaust of the involved engine, but the volume did not seem appropriate when compared with the other engine at the same RPM.. We then went into the heat exchanger and found large calcium deposits. We extracted as much as we could from the inflow and effluent sides, then looked at the exhausts. Again there was more wa
ter exhausting the other engine. The exchange tubes are now in the shop undergoing an acid bath.
I hope to be cruising the Chesapeake on the 4th but I am not sure what year!

We'll be in Hawks Cove off the Magothy. Give us a shout if you come by there.

Bobk