Originally Posted By: blackman777
About 10 years ago I had Delvac 1, 5w-40 in an old Plymouth Caravelle. The temperature was 10 and it barely turned over (and then promptly shutoff). I had to keep my foot on the pedal, even when stopped, to keep it running.
If you're having a problem with starting a vehicle or keeping it running with any 5w-XX (assuming it's plugged in when appropriate) anywhere in North America, it's not the fault of the oil. Battery, fueling, or tune is the issue.
In all my outdoor stored vehicles in all the -40 weather we've had, I've never used anything thinner in cold cranking conditions than a 5w-XX, and it was never an issue. The old Audi had some RP 0w-40, but it was usually indoors anyhow.
When I had a vehicle that didn't start or run right in the cold, assuming it didn't have something utterly silly in it for oil choice, I tended to check things like the battery and connections, alternator output, and fueling (i.e. if a carb, does the choke even remotely work). Oil was the last thing on my mind.
I realize it's tempting to blame the oil, since that's an "easy fix." At least, it's easier and/or cheaper than replacing batteries, cables, alternators, starters, or diving into the fueling system. But, it won't be the oil.