... Leaving thousands of asthmatics dying in their wake.
And what's this we UK-ers hear about Minivans and Cherokee-type vehicles being
classed in the USA as small trucks and allowed to pump out 50% more emissions
than
cars?
PaulH.
Ray McCrary wrote:
>
> Actually, the new high speed diesels that are now in the cars and light
> trucks not only run at comparable speeds, but last a very long time indeed.
> Most of these engines are quite small.
> Ray
>
> At 09:54 PM 11/29/97 -0500, Mere wrote:
> >Hello Peter and List:
> >
> >I must take exception to this "diesel engine thinking" regarding wear on
> >engines. Yes, starting places offers wear opportunities on engines but an
> >engine with good oil and decent oil pressure will not wear unduly at
> >startup. However, the idea that engine life will be enhanced by leaving it
> >running is questionable.
> >
> >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.
> >
> >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.
> >
> >What determines cylinder wear is the simply the number of times the piston
> >travels up and down in the bore. Every one of those cycles causes wear.
> >Why does a large displacement V8 engine seriously outlive a small
> >displacement four cylinder engine? It does less work at much fewer RPM.
> >
> >It is not at all unusual for a small-block Chev or Ford taxicab to
> >accumulate over a million kilometers in service. This is possible because
> >of two things. It is started less often and it does less work because of
> >its large displacement and lower revs.
> >
> >Diesel engines however thrive on steady running and don't like to be shut
> >off because of problems inherent with compression ignition and proper
> >mixture control. Diesel trucks go for millions of miles, not so much
> >because they are diesels but because they run at very low RPM and have very
> >large displacements. If diesels ran at the speeds of our LBCs they
> >wouldn't last much longer relative to the work they do.
> >
> >John McEwen
|