The aluminum thermostat housing and related tubes on my original motor were in terrible shape with major pitting and corrosion, but fortunately the ones from the replacement motor are much better. I still spent some time cleaning them up. I’m not exactly sure why, but these aluminum parts tend to corrode more often and more dramatically on Mercedes than any other car I’ve worked on. Not sure if it is the type of aluminum, the type of coolant used, the change interval, something else, or all of the above. I do know the coolant in the car when I got it had not been changed in a while, so that certainly contributed.
On the left is my original thermostat housing and the cleaned up replacement is on the right. The corrosion on the original was bad enough I was worried about leaks or tightening a clamp too hard and breaking it. First I cleaned with degreaser and soap, then with brass brushes by hand and dremel to eliminate the powdery white corrosion, then a scotch-brite pad to get the rest off. After that I wasn’t happy with the amount of pitting of the aluminum so I sanded the areas where the hoses clamp down to eliminate some of it. There is still some decent pitting but I don’t want to sand much farther and make the material too thin. I put a light coat of anti-corrosion gel on, wiped most of it off, and called it good. Maybe this all will help, maybe it just makes me feel better.
New thermostat installed and a new silicone bypass hose from the thermostat to lower water pump hose. Getting to that hose is such a pain I don’t want to do it again if I can avoid it. A $7 silicone elbow cut to size should do the trick for as long as I need it to last. Or longer.
From now on the car should get proper G05 or Mercedes coolant changed at regular intervals and I’ll check on the aluminum and see if it continues corroding or not.
