On Thu, 01 Sep 2011 07:40:37 -0700, SMS
wrote:

On 8/31/2011 7:13 PM, Ed Pawlowski wrote:

wrote

Please tell me how changing the oil too often is not good for the
engine.
There's some guys out there believe slightly dirty oil is better -
they think the detergent package is "too agrssive". No credible
evidence to support the theory.

They may be correct if you suddenly put a good detergent oil in a '53
Chevy in-line 6.

It's not that they believe that slightly dirty oil is better, it's that
they believe, correctly, that the additives (not just detergent
additives) are in new oil in volumes designed for normal oil change
intervals.

What the manufacturers of motor oil should do is to market an oil
designed for short oil change intervals with lower quantities of
additives, sort of the opposite of the synthetic oils. If you look at
Amsoil, in their flagship product they have such a high quantity of ZDDP
that they cannot get API certification because they contain too much
phosphorus (in the form of the additive ZDDP (Zinc Dialkyl
Dithiophosphates)).

The other option would be to do short-interval oil changes with half
multi-weight detergent oils, and half straight 30W oil (assuming your
engine calls for 10W30). You don't need the quantities of additives
present in multi-weight oil if you're going to change the oil at only
3000 miles, though you do lose some of the low-temperature viscosity if
you dilute the multi-weight oil.

You don't have a CLUE what you are talking about. Some straight grade
oils have a much higher level of additives than many multi-grade oils.
There is NO co-relation between additive levels and viscosity - except
for the VI improvers added to multi-grade oils that straight grade
oils don't get - but they have nothing to do with improving the
lifespan of an oil. In actual fact, Multigrade oils have a SHORTER
lifespan than straight grade oils due to shear degradation of the
long-chain polymers used to stabilize the viscosity. This is another
reason extended drain intervals are not a good idea, particularly with
broad viscosity range oils. Nothing wrong with 10W40 or 20W50 oil
with a relatively short drain interval - but they start suffering
shear degradation around 5000 miles under normal service - shorter
distance under high load and high speed (engine bearing surface speed
- not road speed) use. More pronounced in today's highly stressed,
tightly wound, little 4 bangers.
The fact that it would be better to just do oil changes at the proper
interval is immaterial. There is a big market out there to sell
ridiculous products to clueless people.