Penz 5W-30, 10W-30 and GTX 5W-30 in Canadian winters

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Jan 26, 2003
I have 3 friends that use both pennzoil and castrol gtx all winter long. It can get **** cold outside here. The question is, are they killing there engines faster by using these oils in the dead of canadian winters?
I don't think they are killing their engines. I use Pennzoil 5w-30 in our winters at -25f. I have had no problems. If you have a good battery, dino 5w-30 is good down to -30f.
If the temperature is consistently getting down to -35C in your area, you need to convince your friends to start plugging in their block heaters overnight, or switching to synthetic 5w30 or 0w30. I for sure would not want to be running a dino 10w30 in those kinds of temps. They are most certainly reducing their engine life significantly with each -35 degree start they make (assuming their car is parked outside overnight, if it's inside the garage it's a different story)
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