SL320 Heating Problems

as everyone suggested, theromostat is the first place to look...

it is one out of two, either overcooling, due to a thermostat stuck open, or heater core not getting hot water, due to a sticky mono valve...

a good question to decide between these two causes:

Does the car take forever to get to 80* as well (normal engine operation temp)?

if yes, look at the thermostat first.

if no, look at the mono valve first.

yes, the thermostat is fairly easy to access on the M104, 320.

it will be in front top of the engine, here is a pictorial DIY


http://www.benzworld.org/forums/w210-e-class/1360233-pictorial-diy-thermostat-replacement.html

your intake could be a tad different, but the main concept is the same, the thermostat is in a housing with 3 bolts, 10-13mm each, depending on the year.

make sure you do the job while the car is absolutely cold, preferable after sitting all night, otherwise, you will make a mess, and could burn yourself...

it sounds like your thermostat is either damaged and stuck open, or not there all together...