Cooling header

Engine finishedOne of the problems of navigating a sailboat that draws 6’6” in the shallow Intracoastal waterways in Florida is the inevitability of the occasional grounding. This does not normally cause damage for a long keel boat, because the bottom is mostly soft black mud, but depending on how hard she goes on, it can be a quite a trial to refloat.

With any attempt to refloat, the propeller, which is whirling madly only a few feet from the muddy bottom, is certain to disturb lots of silt and sludge, which can be drawn into an engine water cooling intake and cause havoc. This degrading process can also go on for years, without actually grounding.

Most freshwater-cooled marine diesel engines operate on similar cooling principles. Simply put, cold seawater is drawn in by a pump, and this cools the hot fresh water in the engine, through a heat exchanger. The residual warmed seawater is then pumped out of the back of the boat, usually through the exhaust.

The large mesh filters fitted to most boats’ seawater intakes will capture larger lumps of debris, like sea grass and other debris, but minute particles of sand and sludge can still pass through, clogging first the seawater neoprene impeller pump, then working their way into the engine's heat exchanger(s) and cooling passageways. The first sign of this is often a rise in the engine's temperature, along with a reduction in revolutions and performance.


This exact scenario occurred when we were traversing a short 20-mile section of the Intracoastal between Titusville and New Smyrna, on Florida's eastern coast in 2022 in my schooner, Britannia.

Suffocating fumes suddenly filled the saloon, and I immediately cut the engine, then made an emergency stop by running aground in the soft shallower side of the channel. There was no time to consider anchoring, because I actually thought we were on fire.

All the hatches and portlights were flung open and the breeze soon cleared the smoke, to reveal a cracked fuel pipe on the Perkins 4.236 engine lift pump. This had been spraying diesel all over the hot engine, causing a thick acrid smoke throughout the boat. The break was soon jury-rigged, and I turned to the large primary engine filter to find the 2” diameter wire gauze blocked on the outside - which is where any debris should be - but also completely solid on the inside, something I had never seen before! It was obvious that a considerable amount of muck had been sucked into the engine.

Damaged ImpellerThe plate on the front of the Jabsco seawater pump was removed, and to my complete amazement the impeller vanes had disintegrated and vanished, leaving only the hub on the shaft. This must have happened when the primary filter become completely clogged, causing the impeller pump to run dry, shredding the vanes. There is only one place the broken bits can then go, into the bowels of the engine.

A new impeller was fitted, and the engine used to drag us into the main channel. We then limped back to the mooring field at Titusville at low engine revolutions, because the engine was constantly overheating.

The next day I cleaned the filter and pipes to the pump, but it didn't help with the overheating. We had to restrict the engine to only 1200 rpm, as we trudged back to Britannia’s marina berth 15 miles south. It took five hours.

To further investigate the blockages, it seemed to me to be logical to follow the flow of seawater, from the impeller to the next piece of equipment and then onward.
Oil coolerThe first place the water went was into the oil heat exchanger, right at the back of the engine - naturally, it would be there, wouldn't it? I removed the water hose to the heat exchanger and poked a finger inside - soft rubber and dirt! This meant removing the double-barreled oil cooler, which was no easy task with a bulkhead in the way. I finally managed to get it off the engine, and using long-nosed pliers I pulled as many bits of impeller out as I could then back-flushed the twin pipes with water.

The next path for the raw seawater was to the larger engine heat exchanger, which was also partially blocked with tiny bits of the impeller and lots of sludge. This was when I concluded that there was nothing else for it, but to completely dismantle and clean all the seawater passageways in this big engine.


BeamAll the parts of the cooling system had to come off, to be examined and cleaned. But this was easier said than done because two floor beams had been positioned right over the engine, and it was impossible to get a wrench on some of the nuts. The beams had to come out, so I used my circular saw to make 45o degree cuts on each end, then removed the beams. I glued a sliver of wood on the ends of the beams to make up for the thickness of the saw cuts, then fitted guides on each side of the joint, to prevent the beam slipping off.

HonycombTo get at the exchanger I first had to remove the intake manifold, to be able to reach the nuts to remove the heavy cast iron exhaust manifold, to be able to reach the nuts securing the heat-exchanger… It is at times like this when I would have liked to get my bruised knuckles around the necks of the people who built this boat!

Three hours later I had the heat-exchanger in my hands!  It was not easy to clean the large device, with its inside honeycomb of tiny tubes carrying the hot fresh water to where it is cooled, or exchanged, by the flow of seawater, that is, when there is any!

I counted about 100 1/8” inch diameter honeycombed pipes inside the body, but only about 30 capable of passing water. The rest were blocked with sludge. No wonder poor old “Perky” didn't have any strength, he needed multiple bypass surgery!

RoddingI bought a 24” inch long 1/8” inch drill bit, and carefully rotated it by hand down every tube I could get to, extracting reams of dirt from each. But some of the tubes were so solidly ingrained that I had to drill them clean using an electric drill. This is called “rodding” the tubes, and needs to be done very carefully because if the tubes become fractured, freshwater and seawater will mix and the expensive heat exchanger becomes useless. I then immersed the whole thing in a bath of Rydlyme Marine dissolving fluid. This is a descaling liquid used by diesel engineers to clean inaccessible parts of engines. Then I pressure-washed the pipes until clean water flowed through both the seawater and freshwater tubes.

ThermostatIt was clear that debris had permeated through the whole seawater system, including as far back as the exhaust elbow. I think this must have been building up for a long time on our trips in the ICW, well before our recent grounding.

Another item to inspect was the thermostat, but it wasn't where the engine manual said it was. I then found out that my so-called British engine was a “North American model,” and the thermostat was located under the large header tank at the front of the engine. When this tank was removed, the thermostat was there, or rather the great black blob of muck that was covering it.

By now things were completely out of hand, and I had bits of the motor all over my garage. I thought; “In for a penny, in for a pound,” and decided to remove the freshwater pump, to be able to examine the inside of the block, but to do this I had to remove the thermostat housing bolted on top of it.

Parts storeAll these heavy cast-iron pieces were secured with rusty nuts and studs into the block, and had probably not been unscrewed in 45 years. Some were so welded up with rust I needed a long socket handle, which I whacked with a hammer to break them loose. These I threw away, and bought new fasteners. I also had to cut many of the hoses and lever them off the pipes. I had no Perkins part numbers for these, so I took the old hoses to my local auto-parts store, where I rummaged through the many pipes in their stockroom, for similar shaped pipes. New gaskets cost $130.

Some of the hose clips had actually snapped, leaving the pipes holding on by corrosion and simple friction, and others showed signs of fatigue. The most serious of these were two 4” inch diameter clips securing the exhaust elbow to the large exhaust muffler. These were both broken and the joint was literally held on with corrosion. If it had parted, hot exhaust would have entered the engine bay and easily caused a fire.

Water hose clampsThe correct type of hose clips for pressurized engine pipes are the sort that have indentations where the worm drive engages in the continuous stainless band. The clamps with open slots are thinner and weaker, and liable to fail over time. I replaced twenty-one of these weaker clips.

Drain cocksThe engine block freshwater drain taps were completely seized-up and impossible to open. They were removed, dismantled and cleaned, then the holes in the block reamed out with a drill bit, releasing a torrent of filthy brown water. Clearly, the block also needed cleaning out, so I tipped all the remaining Rydlyme Marine fluid into it and left it overnight, in hopes of dissolving much of the ingrained grime and silt.
Engine parts
By now the engine was looking somewhat naked, with hardly anything on the sides or ends of the block. After cleaning everything with degreasing fluid, I spray-painted the block and all the parts with blue engine paint, ready for re-assembly. At least I wanted my hard work to look good.

I would mention here that all this was in the height of the summer, with daily temperatures in the 90s Fahrenheit, and sometimes over 100F inside the boat. All I had for protection against the blistering heat was the boats air conditioning, which managed to keep the inside temperature at around 80F, otherwise, I would still be at it.


After draining the dissolving fluid from the engine block - which from the looks of it had done an excellent job - I began the task of reassembly, in the reverse order of dismantling, more or less. I couldn't quite remember which pipes went where, and I felt like one of “All the King's men, who couldn't put Humpty Dumpty together again.” It was a good thing I had taken photographs before I started.

On the starboard engine side, first the heat exchanger was relocated, along with its four connecting hoses, one of which was a long copper pipe coiled around the back of the engine to the other side. Then came the bulky and heavy exhaust manifold, which had to be bolted to its equally massive exhaust elbow with new hose clips, to secure it to the muffler. Then I bolted the inlet manifold, to complete that side of the motor.

On the port side, the all-important raw water pump was re-bolted in place, with yet another new impeller and glycerin grease, just for good measure.

Second filterI decided to fit a second water filter directly after the impeller pump, to catch all the bits of any future impeller failure, and anything which managed to pass through the water pump. Worries about this filter restricting the flow were completely dispelled, after seeing the torrent of water being pumped out of the exhaust.

I then primed all the pipes with water, from the seacock through both heat exchangers and exhaust. This would ensure that a circulation would occur the moment the engine fired up, instead of the impeller running dry even for a few seconds.

The freshwater pump was reconnected to the front of the engine with the thermostat housing, which I then filled with fresh water, ensuring that water filled the cylinder head. I checked for leaks in all the pipes and gaskets, and thankfully there were only a few hose clips to tighten.
Then the header tank was refitted and filled, the alternator reconnected and the belt tensioned. The job was now complete - well, nearly.
I had drained all the oil out of the engine sump, by hanging upside-down into the bottom of the engine to unscrew the drain plug. I replaced it with a 90o degree elbow and a reinforced pipe up to a hand vacuum pump, so changing the oil will now be much easier. I filled the engine with new oil, along with a new fuel filter. The transmission was also drained and filled with new oil.

It was now nearing the moment of truth, to see whether the engine would start, but much more importantly, remain at its nominal operating temperature of 180F.
I opened the seacock and gingerly pressed the start button and the engine fired, and all systems were suddenly, go!

ExhaustWithin seconds 60 psi was showing on the oil pressure gauge. An absolute torrent of water was also gushing out of the exhaust pipe, more than I have ever seen on any single-engine boat I've ever been on. But then, so it should be, because the whole water system had been completely dismantled and meticulously cleaned, probably for the first time ever.

It still took a few anxious minutes for the water temperature gauge to begin to move. It slowly rose to 180F then stopped, as the new thermostat opened, allowing for full circulation of water throughout the engine. Whew, what a relief! I engaged the forward gear, and slowly increased the engine speed to 2000 rpm, and with mooring lines bar tight, the temperature remained steady.

Taking Britannia out for a longer trial run was next, and with the boat plowing along at 2,250 rpm, (maximum break horsepower), the engine temperature remained constant. When it had cooled down, I drained the freshwater out of the block and refilled it with a 50/50 mixture of Ethylene Glycol, (antifreeze), and distilled water. Apart from freeze protection, an antifreeze mixture boils at a higher temperature, 230F, than water alone.

This was a long and very difficult revitalization of a 45-year-old engine. It is a fine testament to these heavy old motors that it ran at all. However, I have to say, I wish both the engine and boat builders had given more thought to their customers, who had to work on the boats. Many items could have been positioned for much easier access.

Britannia had been immobile since early May 2022 and it was now mid-August. Being retired, (that is, from an income-earning job, not a boat), I was able to work on her at my leisure, but delays in delivery of parts, repairs, weather, etc., all took their toll on my time. My actual work log showed 130 hours.
You can be sure I will be very careful in the future, to (a), avoid groundings and, (b) if I have one, to immediately check the water inlet filters. I certainly don't want a repeat of this hard labor or the costs.

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