Anyone know if the OEM block heater (winter engine heater) is an oil pan heater or a water jacket heater?
If an oil pan "radiant" type heater, how long should it be left "on"?

 

04 A4 OEM Block Heater is an oil pan patch style heater. One concern of fire with this style of heater comes from patch heater being impacted and physically damaged by road debris. As long as it is installed properly and not impacted, you can leave it on as long as you want as it is effective and fairly low power.

 

Thanks for this! Certainly appreciate the quick response. -35 tonight in Alberta tonight.

Another question if you don't mind. My antifreeze is tested for -30. My understanding with antifreeze is that ratings somewhat higher than acutal temperatures is safe. I.e. antifreeze that tests for -25 is still safe at -30, and so on . . . Thoughts on that?

 

The issue is Coolant can begin to congeal when temp is exceeded. If your coolant tested good for -30C and you have your pan heater plugged in at -35C, you *should be* ok.

If it were me and if any doubt, I would flush coolant system and mix new G12 coolant 60% with distilled water 40% for cold climates and 50/50 for moderate climates. Audi very clearly states do not exceed max mixture of coolant 60 / water 40 mix as coolant performance will actually be reduced by exceeding this spec.