Water Cooling Problems

 After a day sail two weeks ago Peter commented that he had noticed that the engine temperature although not at the overheating zone was a bit higher than he would have expected.  I thought that this presented an opportunity learn how to inspect and replace the engine's raw water pump impeller.  I am ashamed to state that after over 650 engine hours of operation spanning ten years of use I had never inspected, much less replaced, the impeller.  A search through my spares revealed that I had only one used impeller on board, and I suspect that the impeller had been replaced by the diesel mechanic who recommissioned the engine after the boat's refit in 2018.

We had returned to my pen relatively early in the afternoon and had a go at inspecting and replacing the impeller, but I lacked the the tools or know how to extricate the impeller and all that we could do was to look at the impeller from the side and see that it appeared to be in good condition. Sometime during the session Peter commented that he had removed the cover to the raw water filter and found it to be relatively clean.  I replaced the impeller plate, started the engine,  and we found that beyond some feeble sputtering of water during the first few seconds of operation, fundamentally there was no cooling water emerging from the exhaust.  We decided to put the matter into the hands of a real diesel mechanic.  I sent a message to Bruce who managed the refit of Pachuca and has become a personal friend, and soon he arranged for a visit on the following Tuesday by Kevin Woodham, a diesel engine mechanic whom he rated very highly.

That night I realized that we had not primed the hose leading from the raw water filter to the impeller, and I decided to have another go.  I prepared myself by viewing some informative Youtube clips on changing impellers which gave me confidence, and armed with a pair of good needle nose pliers and 240-grit sandpaper I returned to the boat a couple of days later.  On the way I stopped off at Seapower, which after many years has moved on from being a Volvo agent and picked up their last impeller in stock for my Volvo D2-40.  I had discussed my plan with Bruce and we both agreed that regardless of the outcome it would be prudent to have Kevin visit the boat and have a look at the engine.  I also purchased a new anti-siphon valve along the way.

Replacing the anti-siphon valve and priming the inlet  hose did not solve the problem but I think that I did a pretty good job of swapping out the impeller.  I managed to tease out the impeller which was in such good shape that I have kept it as a spare, then cleaned the impeller housing with gentle use of 240-grit  sandpaper and mentholated spirits.  I gave the cover plate a similar treatment.  I then used the trick of using a cable tie to bend over the ends of the new impeller to facilitate its insertion into the pump then coated everything, including the gasket, with the supplied glycerine grease.  I then inserted the new impeller, screwed on the plate, primed the inlet hose, started the engine, and still got no water from the exhaust. At this point I realized that the impeller had never been the problem.

Pump Plate

Pump After Cleaning

New Raw Water Filter, Top Left

On Tuesday morning I met Kevin the mechanic in front of the club house and as we made the long walk to my pen at D81 I recounted the work that Peter and I had done.   At the boat Kevin found the engine in plain view with the cover well out of the way, with the engine and bilge as clean as I could make them.  

Kevin immediate got to work with no interest in the impeller.  His primary suspect was an anode fitted at the rear of the engine behind the heat exchanger that I didn't even know existed.  He told me that the anodes hang down inside of the housing and are prone to blocking flow of incoming raw water when they break up and drop.  He unscrewed the plug holding the anode and sure enough there was a big remnant of it blocking the water inlet.  He then used a screw driver to break up the remains of the anode, informing me that the fragments would be carried off and dumped overboard by the exhaust system.

 At this point I commented that anodes are termed sacrificial because they are supposed to degenerate, so wasn't it a maintenance issue?   A careful search through the engine owner's manual confirmed to me that there is no mention anywhere of even the existence of the anode, let alone its listing in the maintenance schedule.

I then started the engine and although there was a bit more water sputtering out Kevin was not happy and said that air was getting into the system.  I told him that the only sources of air that I could think of were the anti-siphon valve that I had just replaced and the raw water filter.

He then had a look at the raw water filter and what a mess he saw!  There was a crucial rubber seal missing from the bolt used to screw down the lid, and the lid had several hairline cracks.  Worst of all, after thinking that the rubber seal for the lid was missing, he dug out of the channel the remains of the seal which had become rock hard and brittle.  I told Kevin that I was ashamed of letting it get to that state and he replied that these things happen.

We agreed that I would replace the raw water filter and he would use the spare key to enter the cabin and replace the anode at a later time.  I purchased a beautiful new filter from Yacht Grot and the next morning I fitted it then fired up the engine 

Soon I has happy to see big globs of water being belched out of the exhaust every few seconds, an amount of water that I had not seen in years.  I put the engine into gear so that the boat was tugging at the pen lines and took the engine up to 1400rpm while I watched the needle on the temperature gauge slowly climb.  It finally settled at about 197F, under the 200F final mark of the gauge, and well bellow the excessive temperature range starting at about 210F.

Peter commented that he had made things worse by disturbing the raw water filter and I assured him that he had done us all a favor first by pointing out the heating problem in the first place, then by drawing attention to the deteriorated state of the raw water filter, which was under-performing and doomed  to completely fail before too long.

As for me I could not complain, since I had (finally) learned  how to manage the engine's impeller and anode.