Originally Posted by JonM
I change mine every 2 years, when I do brake fluid. It is an easy DIY. The problem with the S65 is there is no coolant drain on the block, so you don't get close to getting all the coolant out. Normally I would change every 4 years, but on this engine with the lack of block drain, I have been going every 2.
+1. Worth doing, and while mileage/how hot it's run are factors age is almost as important, stuff is solubilizing (and coolant becoming more corrosive) whether the engine is running or not, just not as quickly when it's sitting idle