I have a 96 e300d, and the purge plug is right where the top radiator hose connects with the block. It is about a 12 or 14 mil. flat head bolt.

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96 E300d

Not all have the purge plug. Mine doesn't.

Would it make sense to drive the car up a set of ramps, nose high, and idle the engine that way? It might get rid of the air quicker.

Thanks for the help fellas. This forum has really been great. I changed my serpentine belt this weekend, and flushed my coolant system as a result of reading the DIYs.

I couldn't find a plug on mine. I just drove it in a very hilly area and it eventually purged the air from the system.

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Ed
-1984 Mercedes 190D 2.2 5-speed gray market(bought@30,000 miles) (Sold back to original owner@170,000 miles)
-1999 Mercedes E300DT (245,000 miles)
-1999 Mercedes S500 Grand Edition (80,000 miles)