Hi,
I have a pair of TAMD41PA's and change the coolant each year. You should find a small tube type valve on the side of the block that will allow you to unscrew the outer nut and this will let the coolant out. Also there is a plug under the heat exchanger that drains the coolant from there. I also have a plug under my turbocharger to drain as well. When draining remove the coolant cap on the top to allow the coolant to drain quickly. When done pour the new coolant in at the filler cap. On mine the coolant overflow jug needs to show coolant when it is cold. There are two levels marked on the jug, low and fill, if I recall. The coolant when the engine is at normal operating temperature needs to be between those two levels.
The only issue I have is getting to the drains I described above on the Stbd engine as that is the outboard side and can be quite tough to get to. I suggest doing the port engine first as the drains are on the stbd side and you will see/learn just what needs to be done on the other engine.
Good luck.
