190 E cooling issue
 

I am driving a 190 E 1.8 Class from 1992 with 142.000 Km's. Car is doing fine, engine runs OK oil consumption normal
however one thing is keeping me busy;
Last year I replaced the waterpump due to external leakage through the overboard drain . Problem solved, however in that same period I started to smell cooling fluid. I do not see any leakage, nor from hoses nor from the heating radiator. The coolant level drops in a month such that i need to add some cooling fluid every now and then to prevent the warning light showing up. Interior heating system is doing fine. I removed all the air from the system by running up the engine with the heater at max. and added the cooling fluid untill it remained stable (at least for a while).
Checked the oil level stick, no signs of water, the exhaust tends to smoke white smoke a little bit more then usual, particular at cold days. Ignition plug of cylinder 4 seem a little bit more white then the other 3, but in general looks good.
I am surprised by the high pressure in the expansion tank, after filling up to level, when the engine has operated a while the level is significantly lower and at relief of the filler cap is coming way up again. Is this normal? I am still wondering where my cooling fluid is going, I have my doubts about the head gasket.

The 1990 & later M102 engines(USA 2.3) seem to enjoy head gaskets at cylinder # 4. Sounds like you are also having that problem.