Raw Water System Problem

[Eric Fee]

Have '85 Catalina 30' with Universal M25 diesel. Having problem with overheating as the result of the raw water cooling system's failure to spit water out once underway. Have adequate raw water output while idling at the dock, and while in gear initially. After about 30 mins., the raw water output gradually decreases and then ceases. One time the raw water output resumed spontaneously with a decrease in the rpms. After running twice with no problems, another time it gradually ceased and did not resume until the mechanic checked the boat three days later. At that time it operated normally while in slip. Thruhull, filter & pump/impeller appear okay to mechanic. Mechanic advised replacing vacuum break/vented loop as it may have allowed air into the system. Question: Could this be the problem? Any other thoughts appreciated.

 

[Tom Soko]

Not the Vaccuum Break

The vented loop is after the fact. Unless the vented loop failed and all your exhaust water is filling up your bilge (and you'd know it!), that's not the problem. Somehow the engine is not getting or not pumping raw water. Air might have gotten into the closed circuit of the coolant, but you would have overheating all the time if that had happened. Have you checked for barnacles or other blockage in the thru-hull? Is the raw-water filter clean? Is the impeller in good shape, ie no blades missing? Is your heat exchanger blocked? When was the last time it was taken apart and boiled out at a radiator shop? If you've been overheating quite a bit, you might have salt precipitated out of the cooling water and restricting the flow thru the heat exahanger. Is your exhaust riser/elbow in good shape? Has it ever been replaced, as it is probably getting to the point where it would be rusting out from the inside? Is your aqua-lift muffler in good shape? Any fittings loose or leaking? Is there a back-flow valve in the exhaust line (there shouldn't be) that might be sticking? I can't think of anything else, but that should give you a few tings to check out. Good Luck.Tom SokoJulandra, C36 #659