I would use Forte Bio degreaser. its great stuff and works very quickly and made for the job. Probably get it a bit cheaper if you shop around for it in the motor trade.We are going to try a new heat exchanger on our Merlo 40.7 engine. The cooling system must have a load of gunk and sludge in it. One suggestion was to put washing powder in with water to move the oil ?
any thoughts welcome.