Thank you for all your answers. I got a lot of good advices. 

The belt is loose. I can turn the pulley on the alternator by hand but the alternator is supplying enough voltage. The overflow tank level for coolant in the back looks good. I didn't have time to check anything else.

I will keep you informed.

Germain

  ----- Original Message ----- 
  From: John Bange 
  To: Germain ; vanagon@gerry.vanagon.com 
  Sent: Wednesday, October 19, 2005 7:47 PM
  Subject: Re: Engine overheating and no heat from front heater

    Every thing was OK for the first miles. After the engine warm up period, I
    was feeling the good heat coming from my front heater. Hovewer after a while 
    I noticed the heat coming from the front heater was cool and the
    temperature gauge was reading high. The overheating and no heat from the
    Front heater problem was happening when the engine was idling. As soon as 
    the engine is working at normal speed everything is OK.

    Thank you for reading me. Any advice on what could be wrong?

  Sounds water pump related. If there's both no heat in the heater and no cooling at the radiator at low RPM, then it can really only be a few things: 1) water pump isn't pumping adequately, 2) coolant pipes constricted somewhere, or 3) both heater core and radiator suddenly became equally clogged. The second two are pretty unlikely. Cast ye a jaundiced eye upon that water pump. Is it's belt tight? Is its pulley wobbly? Noisy? A cold heater usually rules out thermostat, at least. 

  -- 
  John Bange
  '90 Vanagon
  "We'd tell a monkey how to peel a banana, if he said he was peeling one in a Vanagon."