My son drives a 2006 Five Hundred and I do all the maintenance for the cars in our family. Several months ago, I noticed mocha frappuccino stuff inside the oil fill cap. I found the same mocha frappuccino inside the front valve cover breather hose as well as the rear valve cover breather hose. I cleaned the breather hoses several times and the mocha frappuccino kept coming back. As far as I can tell, there is no blown head gasket which would be the obvious cause of coolant entering the engine oil.

I did a lot of searching on forums and the internet to try to figure out what could be causing coolant to leak into the engine oil. Long story short, I replaced the water pump and the PCV valve and that fixed the problem. Upon removing the water pump, I found signs of coolant leaking into the front head. There was crusty stuff built up where the water pump shaft mounts to the camshaft. It has been a thousand miles or so since replacing those parts and the mocha frappuccino stuff has not returned!

I followed the advice of some youtubers and installed a water pump which uses a bolt in the center of the shaft to mount to the camshaft. Apparently, some aftermarket water pumps lack the bolt but instead rely on a key on the water pump shaft which mates with a slot on the camshaft. The key/slot sometimes fails causing the new water pump to prematurely stop working. The factory design includes a bolt in the center of the shaft so I bought a replacement which has the factory style bolt.

Replacing the water pump is a pretty easy job since it is right on top and bolted to the front head.