1999Audi

Hi
I have a 99.5 A4 2.8 with 139k.
TB job with TB KIT was done by me at 97k in 2011 (Timing Belt, Water Pump(GRAF), T-stat(BEHR 87c) and all rollers from TB KIT + New heater core)


Everything was fine but Today 40k later I see that:
-Engine overheat (water temp gauge go past the middle..a notch) VAG readings shows that temp is going up from ~90 to 114c and beyond
-Electric cooling fan does Not turn on even at 114c, BUT if I turn on the heater it start to work/spin.
-Heater blows very hot air
-Radiator was replaced in 2010
-coolant Level is fine (just checked)

Is it Thermostat that stuck Closed or Coolant Temperature sensor top or bottom (back in 2007 at 73k both sensors was replaced) ?

Anything else I can test?
....I cant drive now because its overheat very fast.

Thanks!

gsjohal

When the engine gets to normal operating temperature, check to see if both the top and bottom radiator hoses are hot. If the bottom one isnt nice and hot then the thermostat is not opening to allow the coolant to circulate.

1999Audi

Just did: temp on the lower hose is cold, temp on the top hose is hot.. so its t-stat probably....

twentysevenlitres

I would say so!
Job can be done without removing timing belt, you just need to slacken it a bit and you can get the thermostat housing out.

1999Audi

Thanks, yes I read about it somewhere. I may try it.