The venerable hardy Yanmar 2GM20 on Triola, my 30 foot, much loved 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), and through all sorts of challenging conditions it has never let me down. Every year, I dutifully service the engine, however, in those services I had never inspected the thermostat. Noting rust around the thermostat housing, I figured it was high time to get the thermostat out. On removal, I was confronted by a very crusty and sorry looking affair. Peering down some of the raw water passages I noted 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 sea dogs of the PBO forums and I discovered Rydlyme. Rydlyme is a non-toxic, biogradable 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”.
Figure out your circuit
The general ideal of this jollop is to mix it at a ratio of one part Rydlyme to one part water and then pump it around your raw water system. Before you begin, we must remove all your engine anodes as Rydlyme will gobble them up, it is however, perfectly safe on most other materials, including, but not limited to, the following:
- Most alloys – The rule of thumb is that if the alloy is designed for use in a water system (aluminium engine block etc), which most marine equipment is, the alloy should be compatible). If in any doubt email Rydlymes technical department.
- Copper nickel
- Stainless steel
- painted surfaces
- Rubber (seals/gaskets)
I sourced the Rydlyme from the good people at French Marine in Brightlingsea who suggested two litres would be ample to do the job.
Now we have our Rydlyme, we need to figure out the route we need to pump this through our engine and to make sure 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 is, once the thermostat is out, 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 we have our plan and a method to prevent our Rydlyme bypassing our engine entirely, it’s time to set up your circuit.
- Remove both your engine Anodes (there is one in the head, and one in the block) else these will get gobbled up by the Rydlyme.
- Remove your water pump by undoing the bolt and pivot bolt holding the water pump on.
- Remove the Impeller from your water pump by undoing the tiny bolts on the back-face plate and removing it with either an Impeller removal tool or a couple of screwdrivers, taking care not to damage the housing. Put the plate back on, taking care to put the bolts back in the correct order.
- Take the inlet pipe off the water pump and attach your hose pipe and little 12V pump with a jubilee clip.
- Remove your Thermostat. Be very gentle with the two bolts that hold the housing on – if you sheer them off you will be in a world of pain (this I know at first hand!).
- Replace the housing without the thermostat in it.
- Take the pipe off the top of the thermostat housing, that goes to the exhaust elbow (or anti-siphon valve more likely), and put a pipe on here, with a jubilee clip, back into your bucket.
- Clamp off the bypass.
- You are all set! Your circuit is complete.
- Next, we mix up our Rydlyme one part water to one part Rydlyme. They inform me the temperature of the water has no bearing over its effectiveness.
- Start pumping (making sure to keep an eye on your battery levels)!
- If you have any other bits (such as your thermostat) that need cleaning. Pop these in the bucket and watch them fizz away and clean themselves up. I also popped my anti-siphon valve in the bucket that looked like it could do with some TLC.
- They 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 the raw water passage ways were clear and my old, grim and crusty thermostat, that I 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 raw water passageways would be in a good condition for my season ahead. Job done!