Your post is confusing and wrong. 5W-30 does thicken less at low temp, but it does NOT thin less at high temp.

Lets look at the grade numbers. 5W-30 is essentially a 5W oil that provides the viscosity characteristics of 30W at operating temp (thus the 5W-30 rating). Similarly 10W-30 is in essence a 10W oil that behaves like a 30W at high temp. The way that these oil achieve their multi-grade properties is via their additive packages. It is a fact that a 5W- oil will flow better and thus protect better at low temp (i.e. while engine is warming up). At high temp, both 5W-30 and 10W-30 are supposed to behave like a 30W oil. However, the 5W-30 relies more on the additive package to prevent thinning than the 10W-30. As the additive package breaks down, the 5W-30 will not be able to protect as well as the 10W-30 at high temp. That is my understanding anyway.

If 5W-30 really did protect as well at 10W-30 at high temp for the life of the oil (5k miles in my case), then I think it would be preferable to use 5W-30 (or even 0W-30) all the time. Maybe if you change the oil every 5k, the additive package really doesn't break down much. This is where my knowledge falls short. I don't know what conditions are required to realize a benefit from a heavier grade base oil. Anyone?


posted by 168.178.1...

• DIY oil changers-What oil do you use?, Boomer, Wed, 15 May 2002 11:10:00
  • Before switching to synthetic, you may want to put a, EricG, Thu, 16 May 2002 22:07:53
  • Re: DIY oil changers-What oil do you use?, Bill S , Thu, 16 May 2002 18:32:02
  • Mobil 1, 0W-40 is best. 5W-30, 10W-30 OK (-), Vlad, Thu, 16 May 2002 14:41:27
  • Amsoil synthetic 5w-30, Mike D, Thu, 16 May 2002 01:05:59
  • Mobil 1: 10w-30 summer, 5w-30 winter. n/m, Gforce, Wed, 15 May 2002 13:13:35
  • Re: DIY oil changers-What oil do you use?, Douglas, Wed, 15 May 2002 12:34:18
    • Re: DIY oil changers-What oil do you use?, BrooksG, Wed, 15 May 2002 14:40:49
      • Oil grades (need an expert - Dick in Falls Church?), Douglas, Wed, 15 May 2002 21:37:31 <-- Viewing This Message
        • Re: Oil grades (need an expert - Dick in Falls Church?), BrooksG, Thu, 16 May 2002 13:51:03
  • Re: DIY oil changers-What oil do you use?, EdinNC, Wed, 15 May 2002 11:30:46

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