Ahh, this brings back memories. Our
MD2B was configured identically. In the reverse gear/transmission there isn't much heat, our experience was that it was growth of
marine life rather than mineral scaling.
For mineral scaling you can use vinegar but it will take a long time (if you can keep it hot that helps) or muriatic acid (available at a
hardware or pool supply). You have to use more care with the acid, both for yourself and the
equipment. If you can figure out a way to circulate either that will help speed things along. Alternatively, a
commercial de-scalant (
ALPACON DESCALANT, Alfa Laval), while harder to find may do a better job.
For
marine growth we were able to rod and wire brush the water
passage in the gear. Get yourself a flexible wire brush about the diameter of the hose and push it through. Takes some
work, but it can be done. The
coolant housing is a loop, so the curves make things difficult, but if you
work from both the inlet and outlet side you can usually get it cleared out. Make sure you flush it well so that your loose crud doesn't end up in the engine passages when you re-connect things.
I would recommend also looking at the water passages in the exhaust
elbow at the same time. It's pretty easy to do, and even if you have good water flow now if the tranny is plugged then it is likely the elbow could use a little
cleaning as well.
Outwest (and anyone else confused),
On the
Volvo MD series with raw water
cooling the water comes from the seacock, passes through
cooling channels in the tranmission/gear, and then goes to the water
pump inlet. As a result the tranny cooling is on the suction side of the
pump, which means there isn't much
head available to overcome blockages (such as barnacles/muscles that decide to grow in there). The OP took the tranny out of the loop and everything was then OK with the engine (but the reverse gear is no longer cooled).
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