Quote:
Originally posted by tkamiya
As I understand it, the overflow tank in the fender well are just that... an overflow tank. Notice, you don't fill your upper tank (where the cap is) to the rim. You fill it about half way. When the pressure builds, the air gets compressed and possibly steam would leave the system, but usually, liquid won't.
This is in contrast with most American and Japanese system where water goes into the overflow tank and goes back into the system when cool.
Mercedes's system is single-directional. Once the steam gets to the overflow tank, it will never return.
AND, I've never heard of anyone cleaning the overflow tank. So, it is likely, what you saw has been there since before the headgasket job was done. Clean it up and inspect it few weeks later....
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Not true! It is a coolant recovery tank. When the system cools a vacuum may develop, and when the cap vacuum relief valve opens it will draw back liquid as long as the bottom of the hose in the recovery tank is immersed in liquid. If there is a leak, a vacuum is almost bound to develop when the coolant cools after operation.
There are two different cooling system design philosophies - one with a "free surface" and the other without. A system with a free surface is thought to purge air more readily, but many OEMs design cooling systems without a free surface and some seem to swap back and forth between both design philosphies. With the vapor vent line from the top of the water outlet to the top of the supplyh tank, the Mercedes design should vent vapor very readily. My own experience is that the system purges air very well after a coolant change.
When I change my coolant I add water to the recovery tank and then siphon it out to remove any debris, but it always seems clean. Has anyone actually removed the tank from inside the fender. It seems that the fender would have to be removed to do so(?).
If you slightly overfill the system it will expel any excess into the recovery tank, and that coolant will remain there and be drawn back into the system if it ever develops a vacuum.
Duke