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I live in Chicago where the night-temperature averages in low 20-degrees-fahrenheit and last year’s (2019) record low went to 23-degrees below zero. To prepare for another (possible) year of low temperature, I replaced the engine oil in my generator and snow-blower with synthetic 5w-30 (API SN).

Questions:

  1. Is synthetic 5w-30 good enough or should I use synthetic 0w-30 instead?
  2. What is the lowest (reasonable low) temperature that synthetic 5w-30 can handle?
  3. Can I leave synthetic 5w-30 over summer since (theoretical) specifications say that it can be used for temperatures as high as 90-degrees-Fahrenheit
  4. What is the downside of synthetic 5w-30 compared to synthetic 10w-30

(BTW, my carburetor is perfectly clean and I have no problem starting at around 30-degrees-Fahrenheit)

Thanks.

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Ideally the manufacturer has engineers that put a lot of thought into this, and the manual spells out all the recommendations for even the most extreme operating conditions. But, lots of times you don't get that, it just says "use 10W40" and that's it.

If I think my operating conditions are likely to be way out of what the manufacturer's recommendations account for, I might deviate from those recommendations. I might use a more viscous oil to deal with the heat, or less viscous oil to deal with the cold. Your conditions in Chicago are typical for huge parts of the country, I bet the manufacturer's recommendations are fine for Chicago. I'd probably leave well enough alone and stick to the recommendation.

If the engine has a lot of miles / hours, and seems to have significant wear, I do switch to something a little more viscous. If a car is burning more than say a quart between oil changes I will suspect it's worn. I figure an engine with some wear is a little looser and will blow by a little more oil (past the pistons into the combustion chamber) so a more viscous oil might make sense, like switching from 10w30 to 20W50, especially in the summer months. I have seen this make a measureable difference many times with high mileage cars.

I haven't really seen the extra viscosity make much of a difference in starting in cold weather. I think the drag you get from viscous oil is pretty minor, better to focus on a good quality battery with adequate cold cranking amps and good cold weather performance if you're concerned about hard starts in cold weather.

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    Thanks. I checked the manual and it said 5w-30 is good. However, in another section it showed 0w-30 for temperatures below 20F (and 23F seemed to be on the edge). That's what got me thinking about 0w-30. My snow-blower and generator are not used much so they have little wear. Guess I can leave 5w-30 in them through summer too. Thanks for your detailed and highly informative response. Appreciated it very much!!!
    – user97485
    Dec 21, 2019 at 17:20
  • The winter weight (0W, 5W) is the viscosity of the oil when cold, both recommended multi-weight oils contain polymers that will increase the viscosity to the same level when heated. The reason the manual specifies a lower winter weight for colder temperatures is to allow the oil to flow while the engine warms up. It's more of an issue in large engines, but Alaskans and Canadians may need to use a snow blower when it's substantially below 20F.
    – Matthew Gauthier
    Dec 21, 2019 at 20:58
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    Matt: Thanks for elaborating on the reasoning behind the fundamental difference between 0w & 5w. The point they made in the manual wrt 0w now makes sense … since they were perhaps addressing Alaska/Canada use-cases. 5w seems good in Chicago. Update: I ran my engine for 15 minutes and then drained the oil completely (tilted it too!!). After adding 5w-30 (and with a clean carburetor), the snow-blower and generator both start very easily with 1-2 pulls at about 30F
    – user97485
    Dec 22, 2019 at 16:34
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Any oil with a 5W rating is good down to -35 deg C, which is -31 deg F. Therefore based a one-time low temperature -23 deg F, you should be fine with 5W-xxx.

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  • Steve, thanks!! That's what I thought based on internet research; however, I wanted to confirm it with folks more knowledgeable and hands-on than myself.
    – user97485
    Dec 21, 2019 at 17:14

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