Swapped my 5W-40 for 15W-40 after a winter in North Dakota

I always thought thick oil meant better protection but after my 2014 Cummins struggled to start at -20°F last January and my buddy showed me the cold flow numbers on the spec sheet, I switched to 15W-40 and the engine cranks way smoother now, has anyone else seen a real difference in cold starts with different weights?

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wendy_lee481mo ago

Wait, did you check if your block heater was even working right before you made the switch? I had a buddy swear by 0W-40 for years but his real problem was a dead heating element the whole time.

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