Mystery regarding raw water on CAT C7s

[BrisHamish]

Hi all,

I am on a mission to have a dry bilge. I am sort of winning the battle...

I have gotten rid of all the fresh water (it took many months to trace all the aircon units draining to the bilge...).

And now I am left with a small amount of raw water ingress. I assume it is coming from one or both of the raw water engine loops.

Engines are CAT C7s, 2006, 1400 hours. Always serviced by CAT annually. Aftercoolers are checked and good, raw water loops flushed with Rydlyme in Feb this year, all raw water hoses new this year in April. When I visually check the engines whilst idling at dock I cannot see any leaks...yet there are new crystal salt deposits under each engine after running out on the bay, plus a small amount of liquid saltwater.

Thoughts as to where or how to check next. Is there some sort of pressure test I could get done??

Thanks all,

H.

 

[Insequent]

Whenever I have had leaks I have always been able to trace back, and see the area of the engine where the leak is occurring by the white salt, or if longer term some vertigris. If your engines are spotlessly clean you may still be able to trace leaks by putting paper towel around potential suspects. This might include raw water pump and oil/transmission coolers, and exhaust mixer elbows. What puzzles me though is when you say under both engines.

Other seawater leak candidates are shaft packing glands and also rudder shafts. I tolerate some water ingress in the former rather than have the packing get too hot underway. Shaft glands may not drip at the dock, but allow water in when under way.

 

[Ski in NC]

Check condensate drains from aftercoolers. A fair amount of condensation can drain depending on operating modes. And yes, check shaft seals, often they do not leak until you get to a certain rpm.

 

[High Wire]

Salt spray from air intakes on the side of the hull?

 

[sunchaser]

As a subset to Ski's suggestion -

Per chance the last time the after coolers were serviced the "0" rings were not installed properly allowing salt water to pass to the condensate drains. Cat after coolers can get problematic if not done right. Salt water check in oil?

Also, maybe the Ridlyme sat in system too long and ate away exhaust elbows that only show leakage at higher RPMs. Paper towels are your friend for locating water leaks.

 

[BrisHamish]

Thanks all for those helpful responses.

We ran both engines up to 2000 rpm today (about 50% load), had some well positioned (and secured) paper towels in place, and here are the results:

On port, at that higher rpm, there is a visible and reasonably significant leak from the main raw water hose basically in underneath the engine where it connects to the engine. One of the clamps had given up the ghost, and the second clamp wasn't much better either. Solution will be to replace all hose clamps on both engines.

On starboard it is more interesting. At higher rpm a faint salt mist eminates out from the mechanical seal on the Sherwood raw water pump, which explains why I find only salt crystals on that side (the mist itself evaporates from the engine heat, so by the time I dock and get down into the engine room there are only crystals left).

So all in all, nothing that $$ cant cure!!

Thanks again for your replies.

H.