I too have a 126 gas car, but with the smaller 6 cyl engine. I recently resolved an air-in-cooling system problem following some advise I found in a post from back when. The process applied to a 124 car, but it has essentailly the same engine as mine. I cannot say if this will help a 560. Perhaps those versed in this engine will add to what I have here. Here's what I did:
- Start out on level surface with a cool engine.
- Remove expansion tank cap and top off coolant if necessary. Leave cap off.
- Start car. Let it idle. Monitor level in expansion tank. If it starts to boil up, etc., shutoff engine. This happens on some Asian models when you try to "air bleed" them. Didn't happen on my Benz.
- After about 15 mins., I saw coolant level rise up a bit. At that point, I turned on the heater to allow complete circulation. Let it idle another 15 mins. with heater on. Coolant rose just a bit more, but never bubbled or boiled out. I allowed car to idle for a total of 30 mins.
- I suspect the air was forced out as the coolant rose.
Maybe this will help your situation.