Egil Kvaleberg writes:
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Engine oil, inherently, lasts just as long as do a gear oil. Indeed, many
modern cars uses an engine oil for the gearbox.
The reason you have to change engine oil so often compared to gearbox
oil, is that the combustion process produces many substances that
contaminates it, and that it is subject to being broken down by elevated
temperatures. None of that occurs during winter storage.
Egil
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Email: egil@kvaleberg.no Voice: +47 22523641, 92022780 Fax: +47 22525899
Snail: Egil Kvaleberg, Husebybakken 14A, 0379 Oslo, Norway
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I agree. And I think that the concept of the oil going bad in six
months' time (or 3 months'time) stems from the manufacturer's
recomendation to "Change the oil every 6 000 miles or 6 months."
(Or "3 000 miles or 3 months as the older car manuals said.)
The 6 months (or 3 months) stipulation is based on the assumption
that the owner will use the auto most every day and if less than
6 000 mles are accumulated in 6 months' time it is because the
daily usage is low. This means a lot of short trips which is
hard on the oil because the moisture and unburned gas resulting
from combustion are not "boiled off".
We, however, tend to let the cars sit (for weeks at a time in my
case) and then take a fairly long drive which gets the oil good and
hot.
So the question is: Does oil go bad just sitting in the engine of
an idle vehicule? (and the engines on the more recent models with
PCV systems are fairly well sealed from the atmosphere)
IMHO the answer is "no". I think that the oil will not accumulate
a significant amount of water from the atmosphere since the
crankcase does not see a vast amount of air exchange. The only
air exchange will be from warm-cool cycling where the air expands
and contracts and that is minimal.
I also think that the most likely oil related problem to be
encountered in a vehicule left to stand for a long time will be
related to the failure of the oil film allowing metal parts to
rust.
Well, I've just exhausted my soap box allotment for the week.
And it's just my opinion. What do I know about oil, I'm an
electrical engineer.
Dave Massey
St. Louis, MO
57 TR3
71 TR6 (oil changed annually, no problems)
80 TR8
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