Using the right size hammer

With Maunie safely ashore in Totnes, sheltering from the rain under her winter covers, we are able to go down to do a few winter maintenance jobs. The latest one tested Graham's nerve, it must be said.

Maunie's four-cylinder Yanmar diesel engine is, like the majority of boat motors, cooled indirectly. What this means is that the engine has a fresh water (with added antifreeze) cooling circuit just like that of a car. However, rather than using a radiator, there's a heat-exchanger that pumps cold sea water through bronze tubes that pass though the coolant in a header tank on the top of the engine. 

The coolant header tank is at the very bottom of this photo

Over time the heat exchanger tubes can become clogged with encrusted salt and other debris, reducing its efficiency and, possibly, resulting in the engine overheating. It was time to take it apart for a good clean and, initially, the process seemed to be going pretty well. I had to remove the exhaust mixer elbow first, to allow access to the aft end cap and to allow the tube-stack to be pulled out. The exhaust elbow and end cap came off without a fight and it was good to find that the bore of the exhaust was nice and clean (they can get a build up of coke which restricts the gas flow).

Flow and return sea water pipes removed at the back of the heat exchanger

The end cap removed, revealing a bit of crud in the tubes

However, this was a boat job so, of course, things then got tricky. The cap at the forward end of the tubes also had to be removed to allow me to prise out both O-rings to allow the tube-stack to slide out. Unfortunately, it showed no sign of shifting once the bolts were removed. I was nervous about applying too much force and possibly breaking something expensive so chatted to the resident engine specialist, Steve, at New Wave Engineering, who has come to our assistance in the past. He climbed aboard and was surprised that the end cap was stuck. However, armed with knowledge and experience, he selected a big hammer and a steel drift and whacked it far harder that I would have dared; thankfully, the recalcitrant cap flew off, undamaged.

With both caps and O-rings removed, the tube stack slid out easily

I had read that brick cleaner (a fairly aggressive acid) or vinegar were both options to soak the tubes in order to clean them but Steve has an ultrasonic cleaner in his workshop which he prefers for the task so offered that as an option.

After a couple of cleaning cycles, the tube stack yields all its hidden bits of scale and muck

The ultrasonic cleaner also removed all the paint from the caps so Steve primed them, ready for a topcoat of Yanmar grey

As good as new

We've bought new O-rings and gaskets so next time we'll refit the heat exchanger and refill the coolant circuit. It's good to know that this job is done and we should be good for another few years. On to the next job on the list!