Super55,
I don't think it has anything to do with the viscosity of the oil but rather the voltage drop that is occuring over the 50 foot cord. A compressor draws a lot of current and even short length cords are not really recommended. What gauge wire is the extension cord? Is the compressor voltage 120V or 240V?
As an example, if the compressor draws 15A - 20A, a 10-gauge extention cord would be best.
As a point of reference, I live in Colorado and have been in my garage shop and started the compressor to pump up inflatable snow tubes when it has been <10 degrees and my compressor starts fine...
Hope this helps...
Burgie
