SL/R107: 1985 380 SL Heating/Ventilation
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1985 Mercedes Benz 380 SL
1985 380 SL Heating/Ventilation
I have a 1985 380 SL with 134K miles that I would like some help with diagnosis. I've owned the car for the past 15 years and have never replaced anything with the cooling system other than fresh antifreeze
The car has mainly been used in the summer months, top down, didn't need heat, didn't need A/C. A recent drive during our cooler whether had me notice that it took a long while to generate some heat in the cabin.
The heater control was set to automatic, temperature control set to maximum
So during a 45 minute test drive this morning on the interstate at 60 mph, outside temperature at 46 degrees F (8 degrees C), I observed the following:
Maximum temperature of hot air discharge out of extreme left and right vents was 124 degrees F
No air discharged out of center vents
Dash water temperature gauge was just over 80 degrees C (176 degrees F)
Thermostat housing read 173 degrees with an IR temperature meter. I was going to replace the thermostat, and in looking at replacement units, they appear to be rated at 183 degrees, which is close to where my car is operating.
In research, I am confused about the center dash vents. I understand there seems to be a high failure rate on these. Should these vents discharge heated air or do they only deliver fresh air? When I lowered the temperature demand, air started to discharge out of both center vents, so they do appear to operate.
This car appears to have a heater control valve and auxiliary pump similar to my 1994 BMW e32 740iL with which I am familiar.
Do I have an issue or am I over reacting?
The car has mainly been used in the summer months, top down, didn't need heat, didn't need A/C. A recent drive during our cooler whether had me notice that it took a long while to generate some heat in the cabin.
The heater control was set to automatic, temperature control set to maximum
So during a 45 minute test drive this morning on the interstate at 60 mph, outside temperature at 46 degrees F (8 degrees C), I observed the following:
Maximum temperature of hot air discharge out of extreme left and right vents was 124 degrees F
No air discharged out of center vents
Dash water temperature gauge was just over 80 degrees C (176 degrees F)
Thermostat housing read 173 degrees with an IR temperature meter. I was going to replace the thermostat, and in looking at replacement units, they appear to be rated at 183 degrees, which is close to where my car is operating.
In research, I am confused about the center dash vents. I understand there seems to be a high failure rate on these. Should these vents discharge heated air or do they only deliver fresh air? When I lowered the temperature demand, air started to discharge out of both center vents, so they do appear to operate.
This car appears to have a heater control valve and auxiliary pump similar to my 1994 BMW e32 740iL with which I am familiar.
Do I have an issue or am I over reacting?
Junior Member
Joined: Jul 2020
Posts: 70
Likes: 11
From: Monroe, GA
1985 380SL
The center vent on US cars is controlled by the Climate Control ECU. Attached is the vacuum diagram showing what is open/closed and under what conditions. The center vent is open in the EC setting, cold or hot, as well as when cooling with the A/C on. If it doesn't open under any setting the vacuum motor is likely bad. This is the worst thing that can happen, as replacement requires the removal of the heater box (it is inside).
Junior Member
Joined: Sep 2020
Posts: 53
Likes: 11
From: Auburn,WA
1958 180D, 1959 190D, 1960 190D,1986 560SL,2007 S550,
I had pretty much the same symptoms on my '86 560SL, the car came from "Bay area", a previous PO had removed the thermostat. I had the same temps, 80C on the hot water, 173F at the thermostat housing...and we were in the mid 40's for air temp. The temp marked on the thermostat is the temp where it starts to open, so it should get warmer for max mileage, power and comfort.
