How to descale raw water cooling system

[tomainsley]

there's a 1959 raw water cooled ford thames trader engine in my boat.
It had previously and a blown head gasket and i noticed lots of rust and corrosion blocking the cooling pathways.
Does anyone know how to clean and descale the cooling pathways, as there is no heat exchanger? Also, what type of acid would be safe; its an old engine and i don't want to dissolve it!
I imagine that as soon as the engine is turned on, any chemicals/ acids would be diluted and flushed out the exhaust. Is there a trick to this?
The only access to the system without dismantling the cooling pipes on the engine exterior to via the raw-water filter.
thanks in advance
Tom

 

[VicS]

A sulphamic acid based central heating boiler descaler such as Fernox DS3 may do the trick but it really needs circulating and of warming up a bit.

With a bit of ingenuity and a small electric pump it is possible to catch the water leaving with the exhaust and return it to the bucket from which the suction is taken.

Rydlyme (Google for it) is a possible alternative to the DS3

 

[cliff]

I will second Vic's comments, a few years ago I cleaned my DV24 using fernox™ DS3 central heating descaler - worked a treat.

I put a bucket in the cockpit and ran a hose from it to the cooling water (raw) on the engine, filled the bucket with fresh water and ran engine, topping up the bucket with more fresh water as needed. Once the engine had run at normal temp for about 10 minutes I placed another bucket below the exhaust to catch the discharge and used a small inline pump to pump this discharged water back to the bucket in the cockpit. I then added the "fernox™ DS3 to the bucket in the cockpit and continued to run the engine under load (well tied to the pontoon) until it was "hot", topping up with fresh as needed. Within a few minutes the water went black as the crud was dissolved and washed out. I continued to circulate the coolant for about one hour adding another bottle of fernox to compensate for losses at the exhaust.
Result was one very clean engine which heats the calorifiermuch better than before and no longer overheats on full power.

It helps to remove the stat after the fresh water flush so there is a good flow through the block / head. As one is recirculating the coolant the engine will warm up even without the stat.

After finishing the cleaning I flushed the cooling system with fresh water for about 10 minutes to remove all traces of the Fernox™

 

[morgandlm]

Use of Fernox

More support for Cliff's solution and method. I would add though that when I discussed doing this with the guys from Bukh they advised against it on the grounds that it could damage the cylinder liner seals. It did not seem to cause any problem with my DV10.
Morgan

 

[SimonD]

Starbrite sell marine engine flushing stuff; the blurb says it will dissolve zebra mussels amongst other things.! Mind you, it does cost £50 a bottle.....

 

[najsmith]

CHeers chaps. I'll look into the acid options for now. Being a small 2-stroke engine I don't imagine she'll need much, but will be good to see that collant flowing again!