Why 12 month oil change on low use vehicle?

TMC wrote:

short journeys put a lot of moisure and soot into the oil which does not get
hot enough to boil off the moisture and the soot from each cold start stays
there .
If you did half a dozen 500 mile trips then you could quite safely leave the
oil change to a higher value.

Did you mean 500 mile trips as you said and not the 50 mile each way trips I
referred to?

Yup, short trips at low revs are extreme usage, cruising down the motorway  
is the lightest usage. Many people get confused by this & then wonder why  
their cambelt's snapped.

TMC wrote:

I did mean 500, but 50 mile trips without the 5 mile trips would do fine as
well.  Even a small car will take a good few miles especially in cold
weather to get the oil up to and maintain a high enough temperature to boil
off all the moisture of a cold start.

If parked outside even if the car wasn't used at all, the oil should
still be changed. Every night when temperatures drop condensation
forms on the block walls. It forms dropplets that run off and drain
into the oil. If not changed a steel sump will rot from the inside and
fall off.
--
Posting from AIOE
replace nospam with skyshack

On 17/01/2011 00:03, Peter Hill wrote:

Out of curiosity, is the engine block airtight when the engine isn't
running?  Just thinking about replacement of air etc, and whether new
moist air can get in whilst the engine isn't running.  If it can't then
there's a limited about of moisture within the trapped air.  Of course,
if it's open to the air, then the amount of moisture isn't limited.

D

like they were saying:

It's very close to being airtight. On a modern engine, every orifice is
connected to something by various hoses. Condensation traps, flame traps,
fume traps, breathers connected to the rocker/cam box etc etc. I can't think
of a realistic way of the engine internals being considered open to
atmosphere. I know some will point to the air intake and the exhaust pipe,
but really, one is so long and tortuous that it would require some humungous
airflow into it, and the other has an air filter and a closed throttle in
the way, so neither are going to be significant. The amount of moist air
that could get in is very close to zero. The idea of droplets running down
the cylinder walls and into the oil is ludicrous.

Steve

On Mon, 17 Jan 2011 23:11:33 -0000, shazzbat  


If only it where so I wouldn't have just scrapped my 2500. It doesn't need  
a lot of moisture, but more relevantly there's a loy introduced every time  
it's started & pootles to the shops,look how much you drain out of an air  
compressor tank.

The air, and the moisture it contains, introduced when you start up goes
into the cylinders and out of the exhaust. It doesn't go below the pistons,
condense on the cylinder walls and then  drip into the oil as someone
suggested.

The compressor is a different animal and not a valid analogy.

Steve

On Mon, 17 Jan 2011 23:37:33 -0000, shazzbat  


Till the engines hot it does, not all of it but some of it, & the crank  
case pulses in pressure & does the same thing. Where do you think all that  
nasty mayo goo comes from?

You've changed the subject again. Mayo forms in the top half of the engine,
not in the crankcase. Cold damp air in large quantities is found in the top
half of the engine, not the bottom half. This is not coincidence, there's a
link.
I say again that there is not sufficient air ingress to the bottom half of
any modern engine to cause this-

"Every night when temperatures drop condensation
forms on the block walls. It forms dropplets that run off and drain
into the oil. If not changed a steel sump will rot from the inside and
fall off."

Which is what Peter Hill posted earlier. Do you agree or disagree with that
claim?

Steve

much like they were saying:


There's also a link between the two. A nice big open link, so oil can
drain back from the head to the crankcase. It's why you see the mayo when
you open the OIL FILLER CAP to pour oil in - and how that oil then FLOWS
TO THE SUMP.

Sorry, I thought we were discussing the issue of condensation in the
crankcase running down and rotting the sump off. The conditions in the top
and bottom half of an engine are very different, despite being linked.
Allowing oil to fall to the bottom is very different from allowing
atmospheric air into the engine, along with it's attendant moisture. [1]
Incidentally, do you agree or disagree with Peter's statement -

"Every night when temperatures drop condensation
forms on the block walls. It forms dropplets that run off and drain
into the oil. If not changed a steel sump will rot from the inside and
fall off."

?

Steve

[1] Apart obviously from the brief time that the filler cap is removed.

much like they were saying:


That's odd. I thought we were discussing oil change intervals on low
mileage vehicles.


In what way? What miraculous effect prevents air from flowing freely up
and down those relatively great big chambers linking head and crankcase?


And, obviously, apart from the crankcase breather being connected to the
airbox. And any inlet or exhaust valves that might be open whilst the
engine's not rotating. And any condensation that may form due to
temperature changes.


I've not commented on it, because I have no opinion on it.


I've never seen a sump rot from the inside out. I've seen them rot from
the outside in, though. I don't find it impossible, but it's more likely
to occur due to the oil becoming acidic and corrosive from combustion
byproducts.

Well thread drift always happens. But I came in to this thread in response
to the question from  David Hearn about what happens when the engine isn't
running, specifically the lack of air ingress.

Yes, I said someone would point to the air intake, check out my first post
in this thread.

Steve

much like they were saying:


Even when the engine's not running?

When the engine's not running and has cooled down, evening out the
temperatures, what force do you imagine is going to create this airflow
which is giving you so much difficulty? As I said in my first post in this
thread, which you have clearly either not read or not understood, the engine
is effectively closed to atmosphere. The air intake has a filter and a
closed throttle in it.

Steve

much like they were saying:


Certainly not crankcase pressure, that's for sure.


Which is, of course, complete bollocks.


The breather is on the intake side of the butterfly - assuming there is
one, of course, which there isn't in one hell of a lot of engines.

Oh, and I'd love to hear you explain how the engine runs at all if you
think the air filter is any kind of effective barrier to airflow.