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
>
>
>
>>DANMAS@aol.com wrote:
>>>
>>> If it's true that 90% of engine wear occurs at start-up, as has been
>>> reported, then you will wear out the engine from starting it long
before you
>>> wear it out from driving it!
>>>
>>
>>I agree that most of the wear occurs during engine startups. During
>>shopping or other stop'n'go errands I leave the car running - providing
>>one of my members is watching. Some might see it as a waste of gas but
>>in the long run it pays back more in parts and engine life. Which
>>reminds me about one of the DieHard battery commercials. A bunch of
>>guys decide to play a game of hoops after dark. In the scene the guys
>>jump out, looking so smart, while the truck's headlight is focused on
>>the ball field with engine off. After the game they get back in to
>>start with no problems - of course. In reality such practice would kill
>>the best battery, starter, alternator, as well as the engine. But I
>>wonder how many watching that commercial actually grasped the truth
>>beyond the obvious: That is don't shut the engine unless you really
>>parked for the day/work or out of sight.
>>
>>Peter Landy
>>'74 Bgt
>
>
>
|