From: C. E. White on

"Scott in Florida" <MoveOn(a)> wrote in message

> That can't be 'good' for an engine...
> I'm wondering if using synthetic oil would help keep damage to a
> minimum while the piston is slappin against the bore....

I run 5W30 synthetic in my Frontier. It made no difference in the
rapping sound on cold morning compared to conventional 5W30. A few
years back a lot of people in an Ford Expedition mailing list I follow
complained about 5.4L Ford engines and piston slap. Ford claimed it
would not hurt durability and based on what people say in that list
have reported over the years, I think it has proved to be true. Some
people in that list tried synthetic to combat the noise - some claimed
it made a difference in the noise, some didn't. I tend to think it
shouldn't. Two lines of thought - when really cold, synthetic is
likely to be less viscous than conventional oils of the same rating
(they should have the same viscosity at 0, but probably not at -10).
This could mean the synthetic oil won't provide as much of a cushion,
thereby increasing the noise. Or, that because the synthetic oil flows
better at really cold temperatures, it will coat the bores sooner and
help dampen the noise. My personal experience was that there was no
consistent detectable difference between a synthetic oil and a good
quality conventional oil. My last Expedition would do the rap very
briefly on cold NC mornings (but cold in NC is not really all that
cold). I played around with different viscosities, and sort of, kind
of, thought that maybe 5W30 Mobil 1 reduced the occurrence of the
noise compared to 0W20 Motorcraft synthetic blend, but honestly I
don't think it is provable.