Overheating or not? 1993 190e

[Paul Bennett]

Temperature guage has numbers at 80 and 120 and a line between which I presume is 100 degrees C. So the spaces between those marks must be 90 and 110.

Putting around town on a 50 degree F day at 30 mph max, the guage goes to 110 at red lights dropping to 90 when traffic flows. Observation while parked, the fans don't turn on (both work) until the temp guage indicates 110...quickly bringing the temp down to 90. NORMAL????

I have tried to remove the overflow tank cap soas to add fluid to the tank while the engine is running and guage is at 90 or above. Attempting to removing the cap (1/8 turn or less) results in scarry scalding volcano situation. Is the overflow tank supposed to be under pressure when the engine is running? Is one supposed to wait 30 minutes before doing adding water? NORMAL ???