On Wed, 4 Aug 2004 14:42:42 -0700, "eh" <eh@nospam.com> wrote:

>I have a 98 Accord that has 80K on it. Last week
>I went an independent deader to get my oil changed.
>The technician told me that I should be filling 10-30
>or 10-40 oil since my car has a lot of mileage on it.
>He said these oil protects older engine better.
>The car manual specified to use 5-30 and nothing
>else. Is the technician right?

You should always follow manufacturer's recommendations. However, the
manufacturer may not include all of the information about oil choices
in the owner's manual, so you may want to check with a dealer. The
dealer will have more extensive information about oil choices that, I
bet, include the conditions under which 10W 30 oil might be a better
choice (high temperature, severe service, etc.).

As a general rule, the lower viscosity oils give slightly better fuel
mileage. Honda engines regularly clock over 200K miles with
appropriate care, so 80K may not be a "high mileage" engine. Modern
oils are so good that there is little reason to change based on age of
the engine. Assuming high quality oil. (And, for what ever it's worth,
every mechanic I know uses Castrol GTX in their own car. That's also
what my Honda dealer uses at oil changes.))

On the other hand, as far as I know, there would be no problem
substituting 10W 30 for 5W 30, especially if the ambient air
temperature is high enough, as for example right now in Austin, Texas,
where we are flirting with 100 degree days.

It is my understanding that 10W 40 oils should not be used under any
circumstances. To get that large viscosity range, oil manufacturers
have to add "viscosity improvers." These are various polymers that
stay balled up at low temperature but unwind and tangle together at
high temperature. When they tangle together, that raises the viscosity
of the oil. If that sounds like it might be bad for your engine, you
should know that experts also think it might be bad.

Anyway, that's what I was told.

Elliot Richmond
Freelance Science Writer and Editor