How much coolant do the 202's require?
 

I purchased a gallon, put it in, but when I read the owners manual, it said it holds 10+ liters or 3 gallons. I also don't know where to fill it to, as there is no fill line. Could anyone offer me pointers? Thanks in advance!

FWIW, I just did a coolant flush on my W202 today. A gallon of coolant did the job, I burped the hoses once the reservoir was half full, at which point I burped the hoses and ran the heater a while, then checked the level, which was fine.

so how did you burp the hoses

Just grab the hoses after the reservoir looks full, and give them a good squeeze or two- that sends air bubbles out into the reservoir. Just don't do it when the hoses are hot!

yea hot lines would be bad lol, i replaced my radiator and it took about a gallon and a half, but seems like it runs warm on certain days

Hmmm how many miles on it? The first thing that comes to mind is the thermostat.

it runs between half and in between half and 3/4 but no higher than that

How many miles on the car? Thermostats don't last forever, no matter what MB might say... On my vehicle, for example, they say to inflate the tires below the tire maker's specs, and that the transmission fluid never needs to be changed. MB engineers are wrong on two very serious counts there. More to follow as I learn more about the car.

128k

Did you do the coolant flush yet? If that doesn't solve the heating issue, I'd think about the thermostat.

i put a new radiator so yae it got new coolant, i can sit at idle and stay at half it never goes up to 3/4

The mechanic who taught me everything I know about cooling engines said you always want the temp around halfway... so FWIW, I'd say you're ok unless there is some special MB temperature, but I've been following the halfway rule for years now, no problems yet. :)