Colin,
The coldest weather I've driven in is about 20F (-7C) and it was plenty hot in the car. How long have you owned your car? I would say you have plenty of good advice here.
I would say to replace the radiator coolant and thremostat, then check the heater core valve.
- Check the coolant. Any idea how old it is? There was a recent post in the last day or so about flushing the coolant. Read all that info, it should be done every few years.
- Check the thermostat. Might be stuck. Easy DIY, something a beginner can do. I know, I've done it!
- Check the heater core through the access plug in the firewall. If this is the problem, I strongly suggest you search the forum for instructions and suggestions on the proper and effecient way to fix this.
If these three typical issues are not the cause, then come back for advanced class and we'll get your car fixed! These heaters do work very well.
Rodd
Powell, Ohio, USA
1966 230SL: arabian gray, natural leather, euro, auto, both tops
1994 E420: pearl black, black leather, auto
2006 C230: alabaster white, 6-speed manual, no options