Is my coolant temp too low?
 

I recently replaced the alternator on my 190E 2.6. In doing so, I disconnected the two coolant hoses to the water pump to gain better access to the tensioner bolt. The upper hose was dry ( engine was cold), I did lose several quarts of coolant (estimated by the spill on the floor)when I disconnected the lower hose.

I completed the alternator job, re-tensioned the belt, topped off the coolant, ran (about 5 min) and burped the system (via the bolt on the t-stat housing)( w/heat on full), now my temp gauge wont hit 80 degrees (seems to stay in the upper 70's) after a 2-4 mile drive. I'm in the Los Angeles area and the temps have been in the 60's during the day.

Is this normal? Or did I get an air pocket? I don't put more than 4k miles a year on my cars....do I need to give a longer distance run ( maybe get a social life?)?

2-4 miles seems to be a bit short for a full warm-up, doesn't it? Take it for a longer drive and see what happens.

riorust, it's odd that the upper radiator hose would have been dry when you disconnected it. You can try burping the cooling system with a cold engine by removing the expansion tank cap and squeezing the upper radiator hose; however, from your description of "cold" running temperature the thermostat may be stuck open. If that's the case you need to replace it with an 87 degree thermostat.

Thermostsats for these cars can definitrly stick open; happened to me.
The brace over the pellet distorted from the load, and cocked the valve open, allowing water flow all the time.
But, seems odd it was fine until you lost/added coolant, and now it's bad.
coincidence?

DG

It may be just a coincidence but these things happen. All W201s I have driven, including 3 of mine, run at 80 deg with the proper thermostat.
I would suspect an airlock first.

What about a 210? My 98 E300D barely breaks 65. Should I investigate the thermostat? Maybe this is why my climate control heater is so weak...

Probably a good bet! You should be hitting at least 80 deg C.