Mere wrote:
>
>....snip....
> I believe, as others have stated, that there are only so many revolutions
> in the life of an engine. Leaving it idling for lengthy periods does not
> allow efficient running as idle mixtures are the least efficient in
> carbureted engines which will add greater products of combustion to the
> oil, and contribute to poor temperature differential within the engine. In
> cold weather, an idling engine will actually cool off if the car heater is
> left on. As manufacturers have recognized, one of the most important ways
> of avoiding wear is to drive the car as soon as possible after cold starts
> so that the warmup is not prolonged. The sooner it is warmed the less wear
> can occur.
Hi John, points well taken on your views. Although I do let my car run a
lil' while before driving, it is contrary to recommended procedures.
Then again since my MG isn't driveable yet I can only refer to my recent
experiences, about 15yrs, with fuel injected and electronic ignition
engines. I tend to keep my RPMs somewhere in the low 2Ks so maybe that
explains why it works for me - yes I am not speaking of MGs.
>
> A cold engine has larger clearances than a warm engine and cold oil has
> higher viscosity than warm oil. Thus the cold oil in the cold engine will
> stick better to vertical surfaces and will fill larger engine clearances
> better than hot oil. As the oil and engine warm the clearances decrease as
> viscosity declines. The real culprit in startup is cylinder wear but
> proper oil and pressure reduces this problem almost instantaneously.
This is the part where I am a bit confused. I would imagine all parts of
a cold engine would contract or shrink more or less equally. So then if
this is true how could additional clearance develop, internally, when
the engine is ice cold?
Viscosity is supposed to be the measure of resistance to fluid movement.
It was my impression that, for example, a SAE 10W-40 oil will act like a
SAE 10W oil when cold, but a SAE 40 oil when hot. Therefore the lower
the viscosity, the thinner the fluid. The oil will remain thin in cold
weather for easy starting and circulation until the engine is started.
As the engine gets hot and reaches operating temperature, the oil will
thicken.
....snip.....
Peter Landy
'74 Bgt
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