Tech talk with Pete today
I was inspired to have a look at Wine-Dark Sea’s cooling system after Sunday’s CYCA Winter Series race (which we won by the way). I saw another yacht blowing steam out their exhaust. We told them and they shut their engine down straight away most likely saving their engine from terminal damage.
So today I checked the cooling system to save myself from similar embarrassment. For the record we still had a health amount of water coming out the exhaust and the engine temperature was in the middle of the gauge. Nothing to worry about, right?
For those not “classically” trained, marine engines draw saltwater in via the saildrive or a skin fitting. There is typically an engine driven raw water pump which pushes this sea water through heat exchangers. On WDS’ engine (Yanmar 4JH3E) there are two heat exchangers, an oil cooler and a coolant cooler. The most common problem with marine cooling systems, apart from sucking a plastic bag in the intake, is blades falling off the impeller of this raw water pump. These blades then typically get caught in the heat exchangers. This is a double whammy as the pump is pushing less water and the blades partially block the heat exchanger.
On WDS the engine is installed backwards compared to most boats with the output shaft facing forwards. This means the raw water pump is hard to get to. It does however make it very easy to get to the oil cooler, the first heat exchanger and the most likely location for broken blades to get caught. So, after closing the inlet valve, I remove the inlet pipe off the oil heat exchanger and stick my finger in to see if there are any issues. So what did I find?
Yep. 6 blades in a heat exchanger that would be no more than 2 inches in diameter. So no rest for the wicked. That impeller will need to come out. So off comes the exhaust elbow. Off comes the inlet pipework and I go arm deep into the engine bay to get the cover off the pump housing. After a short wrestle with the impeller, out she comes.
Ahhhh. Slight problem. There are 7 blades missing and I’ve only found 6. So off comes the rest of the pipework to find the remaining blade. So much for a 5 minute job. Again, bear in mind that this impeller, as bad as it looks, was still pushing a healthy amount of water and the engine was not overheating. You don’t need an engineering degree though to see it was overdue for replacement.
Anyway moral of the story is check your cooling system every year regardless of whether there is water coming out the exhaust. The rubber blades become brittle and, like a lot of things on boats, the less you use your boat the worse they get. A good idea is to take a video of the water flow out your exhaust immediately after you replace the impeller so you have a reference. Another thing is that cooling systems are hard things for mechanics to check when the boat is out of the water (due to the risk of air locks) so often they are overlooked.