Episode 33 Diesel Engine Part 4 - Paint, Acid, Limescale, Thermostats and Anodes

The good thing about paint is that it covers everything in a nice glossy coat. The bad thing about paint is exactly the same - it covers everything, including the parts you might want to see. This seems to me to be something of a disadvantage when, for example, you are trying to figure out what lies beneath. In this case, I needed to take the thermostat assembly apart to fit the new thermostat that had finally arrived from The Engine Room. 

It took longer than the 2 to 6 working days, that I had paid for, to ship the new parts from the Auckland to Brisbane. The Engine Room had placed the order on 30 Dec 2021 and the parts arrived on 19 Jan 2022, which, by my reckoning, is  at least 12 business days, depending on how you count public holidays. Yes, I know it was Christmas, and COVID etc. but of all people who should know how these things affect their business, it is the couriers, and they should advise accordingly. I don’t blame the Engine Room, but I am miffed about not getting what I paid for, in terms of delivery time.

When I took delivery of the rebuilt engine from Diesel Works, it had come in its shiny new coat of paint, but with the thermostat removed. You can see the old and new thermostat and engine elbow in the photo below. It is obvious that the old thermostat was cactus, and had been so for a while.

I needed to take the newly re-assembled housing apart, so I could insert the new thermostat. This is where I got to the problem of paint. Bukh, along with other engine manufacturers, uses many different metals in the construction of its engines. Some parts are softer than others, which makes them more vulnerable to spanner-wielding amateurs, like me, than other parts. The problem with paint is you don’t know which part is made of what until you take it apart. Also, when a part of one type of metal is screwed into a part of a different type of metal, you get the corrosion caused by dissimilar metals, which is especially problematic in a marine environment. I found a good example of this when attempting to remove the old brass barb from the old stainless steel exhaust elbow. There was so much corrosion product in the joint, that I practically destroyed the old barb trying to unscrew it, hence, the hasty addition of a new barb to my shopping list from the Engine Room (the old and new barbs are included in the photo below).

With softer metals, such as brass, you can easily round off the nuts or strip the threads when taking components apart. Some of the parts for the thermostat housing took some persuasion to shift, hindered by the awkward arrangement (what my mate rightly calls “awkwardosity”) of the corrosion-welded components. I resorted to ingenious and unrepeatable combinations of the bench vice and adjustable spanners to grip the part and a large shifter to turn the housing.

Further problems arose from the accumulation of lime-scale inside the assembly, which contributed to the melding of parts that should not have been melded. The Bukh DV10 LME, like the others in its family, is cooled by seawater. It sucks water from the ocean, pumps it around the cylinder block, and pushes it into the exhaust elbow from which it gets blown back into the sea via the muffler and exhaust pipes. The rate of circulation around the cylinder block is controlled by the thermostat. When you heat or boil seawater you are left with a number of residues, including limescale, which is the same stuff that goes into making cement. Limescale, being alkaline, can be removed by an acid.

Being rather fussy about cleaning things before putting them back together, and also needing a clean seat for the new thermostat, I decided to clean the parts in an acid bath. Initially, I was concerned that the acid would eat not just the limescale, but also the parts themselves. After some tentative trials and research, I settled on a concrete cleaner from the local hardware store, because it was mainly Hydrochloric Acid, was relatively cheap and came in a 5 litre bottle. I reckoned on quantity rather than quality, as I did not know how my parts would react. I found that the acid ate the limescale, leaving the metal and paint in tact, so I put the parts in for a soak over a couple of nights to shift the limescale cement and other gunk. The acid might have eaten some of the parent metal, but it was difficult to tell. I thought the loss of any parent metal a fair price for a clean seat for the thermostat, and a general clean out of the tubes.

The acid bath and cleaning revealed that the connectors were brass, the thermostat housing body was copper, and the top piece, which connected them together seemed to be a composite construction with a copper skin and an alloy body. I say “seemed” because it is not clear whether the surface I was cleaning was residual limescale cement, or parent metal. Or something else.

In the disassembly process, the paint to the connections took a bashing. Rather than repaint them, I decided to clean off the paint completely. I like the look of the brass. I know it will not stay this clean and shiny but, in future, it should be obvious that it is a brass fitting, deserving of more care than, say, cast iron.

I reassembled the thermostat housing with new gaskets and replaced the old, crimped water lines. A new set of gaskets from Bukh costs and eye-watering $700, which is way too much to consider every time you need to take off the thermostat housing, or something else. I would only consider a new gasket set if I were to disassemble the cylinder head, which is unlikely. I bought some gasket paper and Permatex Ultra Blue (gasket goo) from the local Auto Shop, and cut out some new gaskets for the thermostat housing with a sharp knife and nail scissors. The fellow in the shop assured me that the paper and goo was good for water, as well as oil.

I also found that the metal used to crimp the water and fuel lines was quite soft, possibly lead or alloy. I needed to remove the crimping and the old lines from the banjo bolts so I could re-use the latter. The crimping yielded to some attention from a wire cutter, leaving the banjo bolts mostly unmarked.

The ambiguous interface between parent metal and limescale resurfaced when I poked around with the engine anode. The anode is, or should be, a removable bolt with a sacrificial zinc body screwed into the end. Provided the zinc is electrically connected to the engine, the seawater cooling water will eat the zinc in preference to the engine. Because of its sacrificial nature, the anode needs to be replaced regularly. Unfortunately, a previous owner appears to have foregone the replacement of the zinc anode, electing instead to screw in a plain mild steel bolt with no visible zinc. The mild steel bolt is 14mm diameter with a 22mm nut on the end and it had been shorted by the addition of a nut as a washer on the outer surface. It also has a copper washer. 

When I removed it, I could see how far the bolt protruded into the coolant gallery around the cylinder head, but was unsure whether the far end of the hole was parent metal or an accumulation of limescale cement. The replacement pencil anode that I had bought was a cylinder with a diameter of 12mm and a length of 37mm, specifically marketed for Bukh engines, but I could only insert it 25mm into the hole, which was the length of the old steel bolt. The question remained about whether I had reached the end of the “real” hole, or if the end had been blocked up with limescale cement. There was no way of telling, without drilling it out. However, if I drilled it, I risked drilling all the way through the wall of the cylinder block, which would kill the engine with certain death and write off the money I had spent on it. 

With the help of a mate, Bill and his pillar drill, I cut off the end of the old bolt, drilled and threaded a hole into the end, screwed the new pencil anode onto the bolt and sawed off the excess length. It was galling to reduce the zinc cylinder from about 37mm to 12mm to get the assembly to fit into the hole. At least I had an engine anode, where none existed previously. Further, I now the means to replace it frequent intervals.

I am now seeking some advice, from anyone who knows, about how deep the anode hole should actually go. My cut-down anode will work, but may need replacing at frequent intervals. It would be nice to be able to insert a full length anode, and leave it longer.

(CORRECTION - I had previously referred to this engine as a Bukh DV10 LSME, but it is, in fact, a Bukh DV10 LME. The "S" is the sail drive version, which this is not).

Old and new replacement thermostat, exhaust barb, exhaust elbow and exhaust gasket.

Old and new replacement thermostat, exhaust barb, exhaust elbow and exhaust gasket. The jagged hole in the old exhaust elbow occurred from previous attempts to fix it.

Example of old water line with crimping. The banjo bolt housing, to the right, needs to be saved for re-use.

Thermostat housing at start of disassembly, showing the gaskets. I'm holding the housing upside-down, by mistake.

Reassembled thermostat housing with new water lines. The blue is excess gasket goo.

Reassembled thermostat housing with new water lines. The blue is excess gasket goo.

Old bolt from the anode socket.

Modified bolt with shortened pencil anode screwed onto the end