Descale an engine
Mark Ryan demonstrates how he cleaned the raw water passages on a Yanmar 2GM20 with the use of Rydlyme
Mark Ryan cleans out his Yanmar
The venerable, hardy Yanmar 2GM20 on Triola, my muchloved 30ft 1970s Albin Ballad, was installed long before I owned her, likely in the mid-’90s: I have never been able to track down the exact date. Through all sorts of challenging conditions, the engine has never let me down.
Every year, I dutifully service the engine: however, in those services I had never inspected the thermostat. So, upon noticing some rust around the thermostat housing, I figured it was high time to get the thermostat out. On its removal, I was confronted by a very crusty and sorrylooking affair. Peering down some of the raw water passages, I noted that about 20% of the openings were blocked with salt and scale deposits.
This can lead to poor cooling performance, eventually resulting in overheating and damage to the engine. Much Googling followed, as well as many posts to the beardy, sage and salty seadogs of the PBO forums – and, as a result, I discovered Rydlyme. Rydlyme is a non-toxic, biodegradable solution that uses some form of chemical wizardry to remove scale as well as ‘rust, mussels, barnacles, zebra mussels, tiger shells and other water-formed deposits’.
Figuring out your circuit
Now we have our Rydlyme, we need to figure out the route we need to pump this through our engine, and make sure that the solution reaches every part of the engine it needs to. The raw water flowing through our hardy little engine will take one of two routes. If the engine is cold, the thermostat will stay closed to help the engine get up to operating temperature and the water will flow through the bypass.
Once the engine temperature rises, the thermostat will open and close as required to let the raw water move around the engine to cool it down (and this is the area we want to descale the most).
With this in mind, simply taking out the thermostat and pumping the Rydlyme through the engine will likely favour the bypass and not actually flow through our engine at all, reducing the effectiveness of the treatment dramatically. The solution to this, once the thermostat is out, is to clamp off the bypass hose to force the liquid through the engine itself. I only had
a standard G-clamp available: however, it is advisable to use a proper hose clamp as that will be less damaging to the hose.
Pump the Rydlyme through your engine
Now that we have our plan and a method to prevent our Rydlyme bypassing the engine entirely, it’s time to set up the circuit. The Rydlyme is circulated using a small 12V submersible pump. n Remove both your engine anodes (there is one in the head and one in the block) or else these will get gobbled up by the Rydlyme. n Remove your water pump by undoing the bolt and pivot bolt holding the water pump on. (Pictured right) n Remove the impeller from your water pump by undoing the tiny bolts on the back-face plate and taking it out with either an impeller removal tool or a couple of screwdrivers, being careful not to damage the housing. Put the plate back on, making sure that you replace the bolts in the correct order. n Take the inlet pipe off the water pump and attach your hose pipe and little 12V pump with a Jubilee clip. n Remove your thermostat. Be very gentle with the two bolts that hold the housing on – if you shear them off, you will be in a world of pain. (This I know at first-hand!) n Replace the housing without the thermostat in it.
n Take the pipe off the top of the thermostat housing which goes to the exhaust elbow (or, more likely, the anti-siphon valve) and put a pipe on here, with a Jubilee clip, back into your bucket. n Clamp off the bypass. n You are all set! Your circuit is complete. n Next, we mix up our Rydlyme: one part water to one part Rydlyme. I am informed that the temperature of the water has no bearing over the Rydlyme’s effectiveness. n Start pumping, making sure to keep an eye on your battery levels! n If you have any other bits (such as your thermostat) that need cleaning, pop these into the bucket and watch them fizz away and clean themselves up. I also popped my anti-siphon valve in the bucket as it looked as though it could do with some TLC. n Rydlyme suggest one to four hours, so I ran the solution for two hours one way through the block, then reversed the circuit and ran it for two hours back the other way.
The results were startling. All of the raw water passageways were clear, and my old, grim and crusty thermostat, which I had assumed was beyond any hope of rescue (I had even purchased a new one from French Marine), came up as good as new.
I was now content that my boat’s raw water passageways would be in a good condition for my season ahead. Job done!
Taking out the thermostat
Waterways choked with deposits
The removed thermostat
The final route our Rydlyme will take through the engine
Cooling water flowing through the block with the thermostat open
Cooling water using the bypass with the thermostat closed
ABOVE: Bypass hose clamped
Undo the bolt and pivot bolt
Attach the hose and the little 12V pump
The circuit complete and ready to start pumping. You can pop any other bits that need cleaning (such as your thermostat) into the bucket of Rydlyme and watch them fizz Pump and return in the bucket, ready to go I also dropped my anti-siphon valve into the bucket
The treated thermostat next to the new one
The thermostat before treatment