I got out to the boat on the weekend and flushed the motor with Rydlyme Marine Bio-Descaler. I removed the thermostat and put the housing back on. Rigged up a 12v bilge pump in a 20L bucket and connected the pump to the inlet side of the water pump (after removing the impeller). Used a hose pinch-clamp on the bypass hose so the pump only circulated through the block. Disconnected the water injection hose to the exhaust elbow and connected a new hose to that hose and ran in back to the bucket, completing the circuit.

Started off with about 5L water in the bucket and let it pump through. Then added 5L Rydlyme to the water. As soon as the 50/50 mix was coming back into the bucket it was frothing and fizzing... lots of good reaction. Let it run for about 90min, then flushed with about 60L fresh water into a new buck so I could see all the Rydlyme was gone.

Reconnected everything and put the impeller and thermostat back in and ran the motor. Got up to 60?C then dropped to 56?C and stayed there. Took it for a run at about 2/3rds throttle and it never moved from 55-56?C. In the last photo, the OzTherm gauge is attached to the block, and the traditional gauge is using the engine temp sensor. Prior to the flush the block temp would run at 87?C and the cooling system temp gauge would go up and down between 50-90?C. So the Rydlyme flush obviously did the trick!

FYI. I left a few bits of rubber (old thermostat seal, o-ring, old impeller) in the undiluted Rydlyme in a tub for around 2hrs... the Rydlyme had no effect on them at all. No black coming off, no sliminess, nothing at all. So would guess the rubber o-ring seals for the wet-liners are fine too

Hope any of this is helpful to those out there needing to descale their engines. Wasn't' too tricky and it's quite rewarding to see your engine running at lower temps.

Goff,
Good results well done. My impeller puller arrived so I am going to give my internals another descale as I didn't get rid of all the scale with the first go. My Bukh thermostat appears original and probably is at $150 replacement cost, I hoping a descale in the bucket then functional check will stop the need for replacement. I will use Rydlyme this time as well, thanks for this thread.

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Thanks Geoff
What type/capacity bilge pump did you use? Did you need an impeller puller or did it come out easily?

There is no need to pull the water pump apart. Just connect a pipe to the outlet side of the pump. The pump body will always be seawater temperature so there will be no calcium build up.

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julesmoto said..

Thanks Geoff
What type/capacity bilge pump did you use? Did you need an impeller puller or did it come out easily?

I just used my fingers to pull the impeller out. But yes, as Ramona said, there's really no need to run the flush through the pump... it was clean as a whistle. I only did it cause it was time to replace the impeller.

I think the pump was a 500GPH. Just a cheap $30 one from BCF.

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EastCoastSail said..
Goff,
Good results well done. My impeller puller arrived so I am going to give my internals another descale as I didn't get rid of all the scale with the first go. My Bukh thermostat appears original and probably is at $150 replacement cost, I hoping a descale in the bucket then functional check will stop the need for replacement. I will use Rydlyme this time as well, thanks for this thread.

I bought a new thermostat cause the old one was really scaled up and stuck half open. Then I put the old one in the Rydlyme... it freed it up completely. Hopefully you can avoid buying a new one!

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Ramona said..
There is no need to pull the water pump apart. Just connect a pipe to the outlet side of the pump. The pump body will always be seawater temperature so there will be no calcium build up.

Thanks. Haven't been to the boat for a week and had trouble visualising it.

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goff said..


I just used my fingers to pull the impeller out.

I think the pump was a 500GPH. Just a cheap $30 one from BCF.

Thanks :)

I have owned my boat for six months. I couldn't pull the impeller at the last service (pump housing faces away from access hatch) so I have waited until the puller arrived. So I will service the engine, descale
and replace impeller etc all at the same time. $30 bilge pump is also a good idea.

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EastCoastSail said..
I have owned my boat for six months. I couldn't pull the impeller at the last service (pump housing faces away from access hatch) so I have waited until the puller arrived. So I will service the engine, descale
and replace impeller etc all at the same time. $30 bilge pump is also a good idea.

The impeller is easily removed with two screwdrivers. Search Youtube for a suitable video.

Thanks Ramona, but I now have a puller.

Rydlyme is no longer available from the distributor as they have supply issues. They now sell Solverbio Scale Break as an alternative. I bought 5L.

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goff said..
Used a hose pinch-clamp on the bypass hose so the pump only circulated through the block....


Just wondering why it is necessary to remove the thermostat if you are going to pinch off the bypass.
Got down to the boat to do this today but then realised that I would probably end up with all sorts of (gasket) leaks if I removed my thermostat housing as the bolts appeared to be a bit rusted on not to mention poorly accessable. It may even have resulted in a bolt shearing so I wasn't too keen. I'm thinking if I don't have to remove the thermostat the job becomes a whole lot easier and the block itself will still be descaled. Anyone got any comments?

With the thermostat in place and closed with a cold engine there should be a small bypass hole , about 2mm, that should allow the acid to pass through.

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Ramona said..
With the thermostat in place and closed with a cold engine there should be a small bypass hole , about 2mm, that should allow the acid to pass through.

Thanks Ramona. So my little 500 gph bilge pump in the bucket of acid mix will be working hard to try and push the acid through the block and exhaust manifold then a mere 2-mm bleed hole in the thermostat which hopefully hasn't become en-crusted. The net effect I guess will be that the acid mix passes very slowly through the motor with greater soak time which may not be bad. I guess I'll know if that 2 mil hole is totally inadequate as there will be next to nothing coming back into the bucket.The bypass passages won't be cleaned but as they are lower temperature when the engine is operating they shouldn't be encrusted. Am I correct?

I would just hook up the hoses in the air so they are above the engine. Blow out the residue water and put in a mixture of acid and let it soak for awhile. Hook up the hoses and run the engine. Then run the pump/bucket/acid routine after as in the youtube videos. With a raw water cooled engine the calcium build up is near the thermostat housing. My engine is a heat exchanger Beta and I don't even take out the anode. I have only cleaned it once so far and I just used the soak method.

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Ramona said..
I would just hook up the hoses in the air so they are above the engine. Blow out the residue water and put in a mixture of acid and let it soak for awhile. Hook up the hoses and run the engine. Then run the pump/bucket/acid routine after as in the youtube videos. With a raw water cooled engine the calcium build up is near the thermostat housing. My engine is a heat exchanger Beta and I don't even take out the anode. I have only cleaned it once so far and I just used the soak method.

Thanks :)