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RE: overheat light blinking
There have been several posts regarding blinking overheat lights when
To be slightly more descriptive: the light is more a "cooling system problem"
light. In the '91 200 (and I'll assume other recent vintages) the light is both
for coolant level and engine overheat. What you are experiencing is the
tripping of the "low coolant" switch and can be solved as described earlier by
topping off your coolant.
My recommendation would be to check the anti-freeze concentration (ethylene
glycol or specific gravity, etc) before adding just water or coolant (phosphate
free -- NO DEXCOOL-- it's incompatible!).
The overheat part of the circuit comes off the multifunction temperature
sensor/switch and is branched off the cooling system warning circuit. Oddly
enough the temp gauge/sender is not connected to the overheat warning. The
gauge is a separate part of the switch/sensor.
You can get a cooling system light because of low coolant AND/OR high coolant
temps. You may or may not also get a corresponding high temperature indication
on your temp gauge. Or you could just get a very high temp reading without the
overheat light coming on.
BTW: simply because your Auto-Check circuit calmly scans through all systems,
then gives you a pleasant "OK" doesn't necessarily mean all is well. My
overheat/coolant circuit is currently dead (no power on the wire), but I still
get the "OK".
This info applies directly to the 200's. But I assume (rather foolishly) that
Audi used some consistency in their designs.