I work in extreme cold temperatures over the winter (-40 isnt a suprize, -30 celcius average). I have two block heaters and have them both plugged in over night. What is a good weight oil for me to use? I read 0-5-10w30s are good to use in temps below +20F...is that true?

 

10w30 works great here in michigan for the winter. I wouldn't go much thinner than that. but your in temps that even colder than i am so maybe you will need to. but with 2 block heater and as long as your glow plugs are tip top and your battery are perfect i don't think you will have any problems. i usually run the 10w30 and plug my one heater in on a timer set for about 3 hours before i leave for work and it fires like it 70 degrees out