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I have a 5.3 Triton 3V that asks for 5W-20 in the manual, but I live in a very hot climate, where the lowest this season is 20~ celsius and the hottest is 45~ celsius. Will switching to 5W-30, 10W-30 or 5W-40 oil be better, and if so how thick should I go, thanks in advance. P.S the engine is on 250k kilometers if that makes any difference.

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Generally, do not change the oil from what is recommended. The main thing this has to do with is the variable valve timing (VVT ... or whatever Ford calls it). If you go to a heavier oil, you will be causing issues with it. If you've taken care of your engine throughout its lifetime, continuing to run the 5w-20 shouldn't cause a bit of issue.

Another problem with heavier oil is, it doesn't flow as well as the thinner oil. Since your bearings are gapped for the thinner oil, running heavier oil may actually starve the bearings of the amount of oil they need. You could actually harm the engine by doing this.

NOTE: Take a look at your owners manual (or find one online). You may be surprised to see it may say to do exactly as you've stated (heavier oil for hotter conditions). If it says to, then by all means.

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    Thank you! This is really helpful Commented May 3, 2023 at 22:03
  • Oils these days are amazingly high tech and very capable of handling wide outside temperature ranges. The days of using different oils in different seasons are long gone.
    – Jon Custer
    Commented May 4, 2023 at 15:15

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