300ce Heater Needs Help ('91)
 

The problem here is even when the car has been idling for 10 minutes or so the temp still reads about 80*- 85*...and is cold as ice...not a sign of heat. As soon as I hit the gas strongly while driving, the heat comes on, while not blasting, its still hot. This just doesn't seem normal. Do these models take a signifigant length of time to warm up? Living here in New England it is a necessity to prewarm any car in the winter. I've not experienced this with my '84 380SL...any ideas? I still wonder if there is a restricted flow going through the heater core...? Water pump and thermostat replaced within last 5K miles. Not sure about the age of the 2 aux. water pumps though. Thanks,
JEFF & JO

Have you checked the monovalve? I don't know what to check. If you haven't replaced it in a few years maybe just replace it.

By the time the coolant temp gauge is at 80*C there should be more heat than you can stand. Check if the AC compressor is engaged when it shouldn't be?

Do coupes have two aux pumps? Why would you need two aux pumps to feed one heater core? Is this a Euro model?

Sixto
87 300SDL

This year is shown as having 2 aux. pumps...I guess to boost the flow to the heater core while the engine is idling. It DID seem like the AC was running...how to check this? Does the compressor disengage visibly when its turned off? I have no experience with this engine. Many thanks!
Jeff & Jo

The front plate of the compressor doesn't turn with the pulley when the compressor isn't engaged.

Sixto
87 300SDL

Check that the auxiliary water pump (below the coolant overflow tank) runs when you're in the Economy mode, dialed for heat ... 75 degress or so. When things are operating normally you should have heat a few minutes after starting ... or within a quarter mile, whichever comes first.