Heater temp question

[32V MERC]

I was wondering if anybody else has noticed this. Last week while driving at night in 5 degree temp, the car was at full operating temp and heat from dash vents was very hot and operating great. Every time I stopped in traffic the temp would quickly begin to drop and become cold. As soon as the engine revs picked up the heat came back and stayed until I stopped again. I originally thought it might be a vacuum problem but noticed no changes whatsoever except for the temp change. Any suggestions or comments?

[32V MERC]

Come on guys I need some input here. Its very strange everything seems to work perfectly except the temp at the registers drops drastically when coming to a stop. Then when engine speed picksup the temp goes back hot again.

[Shora]

Start with checking the coolant level and burping the cooling system.

[fastblackmerc]

Start with checking the coolant level and burping the cooling system.

What he said.

[Drewstang]

I had the same issue not long ago. I had to back flush my heater core, then burp the system to resolve it.

[GordonB]

32V Merc,
I'll chime in without asking you to 'burp the baby'. The car puts out more air thru the heater/floor vents moving than standing still -- this is a fact. Also when the outside air is 5 degrees above/below ZERO, it's frigin' COLD outside! Poor Mm is a metal can without a lot of insulation. That cold penetrates the car jus sitting there even if you have it warmed up and Heat is set at say, 72. You have to up the blower speed IMHO if you sit very long idling. Ask me how I know -- I have 2 MMs and 1 wife who is always cold. My MMs don't need burping, but when it is cold out, .... FWIW.
GordonB

[32V MERC]

Thanks for the info guys I will be burping first thing Monday!