60F
Member
I have twin Volvo TAMD61's on my Princess 435. The Chief Engineer and I started servicing the engines about three months ago, but then I became unwell before we could complete the changing of the antifreeze which we finally did yesterday as my health has improved. As we had had the boat lifted at Port Solent to fit new anodes, we ran her out to sea for about 30 minutes to check the engines were OK before returning to Gosport. The engines performed without any obvious problems as she ran up to cruising speed of 2,200 rpm with charging, oil pressure and temperatures on normal.
The last coolant change was two years ago with a 50/50 mix of good quality blue antifreeze normally used on trucks. The antifreeze drained at that time was normal in colour, the only issue noted was that we could not find a way of getting the amount of water quoted in the manual out of the engine, only around 21 litres had come out of the port engine, with a bit more out of the starboard as it has a calorifier. To take account of the fact that there would be some water still in the engines, we upped the amount of antifreeze to give a theoretical 50/50 mix based on the amount of coolant that the manufactures stated would be in the engines. We also fitted about 5m of reinforced automotive heater hose between the engine and calorifier to replace the existing hose that was beginning to leak slightly. Although work commitments have meant that the boat has managed less than 40 hours use in the two years, neither engine has needed to be topped up in the intervening two years.
The change on the port engine went well, although we were surprised that the coolant that came out of the drain hole midway down the side of the engine was almost clear whilst that that came from the drain hole at the front of the engine was significantly bluer. There didn't seem an obvious explanation why the colour was not consistent.
When we drained the starboard engine we were horrified to see that the coolant was a dark brown / black colour, similar to dark dirty water after cleaning a dirty car. However its consistency was like coolant rather than oil (which anyway would have been a much darker black) and there was no sludge. There was no evidence of any oil on the surface of the coolant extracted - other than the colour it appeared normal. We ran out of time to perform any further tests, but having changed the oil around three months ago when the work started, we are fairly comfortable that there was no sign of any cross contamination at that time (though we will check again next time we visit the boat). There is also no sign that either engines have overheated and displaced coolant from their respective expansion tanks, something that I would have expected if exhaust fumes were directly contaminating the coolant. I have a block tester at home which I will take next time I go down to the boat. This is basically a tube that fits over the expansion tank filler neck which is filled with a blue fluid and has a pump at the other end which enables you to suck fumes out of the coolant when the engine is running at operating temperature and through the liquid which turns it orange instead of blue if combustion gases are present. I've used this on a couple of petrol cars before, but never a diesel boat.
Friends have suggested that possibly the antifreeze used two years ago reacted with whatever had previously been in there, noting that we had not flushed the engines because we were perplexed at not being able to fully drain them. This is possible, but does not explain why one engine seems fine. Similarly, someone did suggest that perhaps the old antifreeze had been weak (we don't know what quality, how old, or what strength it was) and that putting a higher strength in has just flushed out the system. A suggestion was made that perhaps the automotive heater hose was of poor specification and has degraded. We will remove and check the interior of the hose on the next visit as it could be a factor as it is fitted only to the starboard engine. All of these suggestions I quite like as they seem to have cheap solutions!
We have also noted that the starboard engine has always run slightly hotter than the port one, albeit always within specification. This has been put down to potential inaccuracy of the gauges / senders and manufacturing tolerances.
Sorry for the long pre-amble, but my question is whether anyone has ever experienced their coolant going black and if so what was the cause? Also, if the block test proves OK, is it worth filling the engine with fresh water and draining (say) four times, refilling with an antifreeze mix calculated at 50% based on the manufacturers coolant capacity, and monitoring her every few hours for the rest of the season (or until it is evident that the problem has not gone away) by taking regular samples of the coolant.
Thoughts would be much appreciated.
The last coolant change was two years ago with a 50/50 mix of good quality blue antifreeze normally used on trucks. The antifreeze drained at that time was normal in colour, the only issue noted was that we could not find a way of getting the amount of water quoted in the manual out of the engine, only around 21 litres had come out of the port engine, with a bit more out of the starboard as it has a calorifier. To take account of the fact that there would be some water still in the engines, we upped the amount of antifreeze to give a theoretical 50/50 mix based on the amount of coolant that the manufactures stated would be in the engines. We also fitted about 5m of reinforced automotive heater hose between the engine and calorifier to replace the existing hose that was beginning to leak slightly. Although work commitments have meant that the boat has managed less than 40 hours use in the two years, neither engine has needed to be topped up in the intervening two years.
The change on the port engine went well, although we were surprised that the coolant that came out of the drain hole midway down the side of the engine was almost clear whilst that that came from the drain hole at the front of the engine was significantly bluer. There didn't seem an obvious explanation why the colour was not consistent.
When we drained the starboard engine we were horrified to see that the coolant was a dark brown / black colour, similar to dark dirty water after cleaning a dirty car. However its consistency was like coolant rather than oil (which anyway would have been a much darker black) and there was no sludge. There was no evidence of any oil on the surface of the coolant extracted - other than the colour it appeared normal. We ran out of time to perform any further tests, but having changed the oil around three months ago when the work started, we are fairly comfortable that there was no sign of any cross contamination at that time (though we will check again next time we visit the boat). There is also no sign that either engines have overheated and displaced coolant from their respective expansion tanks, something that I would have expected if exhaust fumes were directly contaminating the coolant. I have a block tester at home which I will take next time I go down to the boat. This is basically a tube that fits over the expansion tank filler neck which is filled with a blue fluid and has a pump at the other end which enables you to suck fumes out of the coolant when the engine is running at operating temperature and through the liquid which turns it orange instead of blue if combustion gases are present. I've used this on a couple of petrol cars before, but never a diesel boat.
Friends have suggested that possibly the antifreeze used two years ago reacted with whatever had previously been in there, noting that we had not flushed the engines because we were perplexed at not being able to fully drain them. This is possible, but does not explain why one engine seems fine. Similarly, someone did suggest that perhaps the old antifreeze had been weak (we don't know what quality, how old, or what strength it was) and that putting a higher strength in has just flushed out the system. A suggestion was made that perhaps the automotive heater hose was of poor specification and has degraded. We will remove and check the interior of the hose on the next visit as it could be a factor as it is fitted only to the starboard engine. All of these suggestions I quite like as they seem to have cheap solutions!
We have also noted that the starboard engine has always run slightly hotter than the port one, albeit always within specification. This has been put down to potential inaccuracy of the gauges / senders and manufacturing tolerances.
Sorry for the long pre-amble, but my question is whether anyone has ever experienced their coolant going black and if so what was the cause? Also, if the block test proves OK, is it worth filling the engine with fresh water and draining (say) four times, refilling with an antifreeze mix calculated at 50% based on the manufacturers coolant capacity, and monitoring her every few hours for the rest of the season (or until it is evident that the problem has not gone away) by taking regular samples of the coolant.
Thoughts would be much appreciated.
