cold running, poor heating (searched already)
 

with the winter season just around the corner, I have noticed the problem coming back that I had experienced last winter.
On the 87 260E:
Two thermostats have already been replaced with no luck. both behr models by mercedes dealer.
here's the symptom.
car's temp needle reads perfect (about 85 deg) when the car is at idle, but with the cold temprature outside, around 55 degrees, the moment the car starts to drive at 15mph or above the engine temp drops, and the temp needle starts to read 80 deg constant. doesnt fluctuate.
the drop in the temp. results in poor heating inside the car.
any ideas would be appreciated.

There isn't much wrong with 80DegC constant while moving.
I can't remember off the top of my head if that model had a heater booster pump or just a valve for the heater.

If you have a booster than you'll need to check that it is working.

Does you heater work ok when the engine is at 85 DegC?

the heater works perfect when at idle and the needle shows 85 deg. it's when the car starts moving and attains speed when the engine temp drops to 80 deg and the hot air blowing in the cabin changes to mild warm.

80 deg. C should be more than enough to get the heat up inside the car. I suspect you may have air in your cooling system or a dirty/blocked heater radiator.

Also try checking that you're air blend flaps are adjusted and operating properly. That could be why it's colder when you start moving, because fresh air is being fed in the vents quicker resulting in a cooler air temp.

Just a thought

Sounds like it could be in the ventilation system, as well you may want to check your auxiliary water pump. It is responsible for circulating the hot water through the heater core assembly. :cool:

Thermostat stuck open!

two thermostats changed already, same symptoms.
could it be that different companies, behr versus others have different operating tempratures ?