weekend thrill raw water problem

[Nick]

On a weekend day cruise the temp of one of our 671TIs starts to rise fast and then the engine exhaust suddenly gets louder than normal. A quick run to bilge and SURPRISE. One of the new hoses on the raw water cooling system at the pipe between the raw water pump and the intercooler came off the pipe. The engine had not overheated and a quick fix I assumed. Lots of water dumped into the bilge. I remove the bracket holding the pipe and reset the water hose thinking it was the end of the story. Underway again at gradually up to 2000 RPM engine runs cool a few minutes and then same problem. Reinstalled the hose again and idled home at engine temperature of 175F.

I am scratching my head because there is apparently a significant blockage in the raw water cooling circuit. The cooling system was taken apart in the spring of 2004. The radiator shop boiled the heat exchanger core, the intercooler was mechanically cleaned, the gear cooler was acid dipped and a new fuel cooler was installed with all new hoses. The engine had been running at about 180F in cool NE water.

I have a feeling that critters may have grown in the exhaust elbow shower head or somehow got through the raw water perko strainer. I plan to head to the boat today and run it at fast idle to determine whether the water pressure is building up in the hose connected at the exhaust elbow or elsewhere. If so, I was thinking of adding HCL acid solution directly into the 2 inch fitting where the raw water hose connects to the exhaust elbow, before a I take the system apart again. Alternatively I could try to flush the system as Karl has described in the past.

I believe the exhaust elbow is monel or SS. Should it be replaced over time even if there are no leaks? Does the showerhead mechanically fail and block flow?

Any suggestions on troubleshooting the problem?

[MikeP]

The showerhead has a series of holes around its periphery. They can clog with whatever junk may be available - pieces of silicone from poor gasket-making, gasket pieces, general casting slag from the engines - whatever. I found what appeared to be a small rock blocking one of the holes!

[Nonchalant1]

The intercoolers could also be blocked up, as they're the first thing in the raw water system.

What type of clamps were you using? Two "T-Bolt" style clamps together may be required if the connection is a little loose, even if there's no blockage. Mine is so hard to get the hose on the barb that it takes two of us to do it.

Doug Shuman

[Nick]

The shower head! Took it off last night once it was clear that the pressure was buidling up in the 2 inch dia hose that dumps the water into the elbow. The intercooler is clean. The series of openings in the shower head were significantly blocked with what appeared to be calcium carbonate shell bits and debris. A small welding rod and a dip in a 50/50 solution of hydrochloric acid with a water flush did a good job cleaning it. No unusual water pressure appears to be buidling up in the system while running dockside. This was alos the likely source of the temp creep I noticed lately at over 2050 RPM. It is amazing how the crap gets there past the strainers. The downside was that the turbo blades look a bit beat up and it will require attention very soon.

Thanks for the help.

Nick