|
Grex > Cars > #121: The Winter '02 Car Care Item |  |
|
| Author |
Message |
| 25 new of 184 responses total. |
mdw
|
|
response 122 of 184:
| 
Mar 2 03:39 UTC 2002 |
The first generation of american diesels ended up with a bad reputation.
The GM V8 diesel of ca. 1980 was basically a gasoline V8 turned into a
diesel, and it turned out to be under-engineered for what it was
supposed to do. A properly designed diesel engine really has to be
designed from the ground up to be more robust, because due to the higher
compression ratio it's under quite a bit more stress. Diesel engines
also have a narrower power band; which means they really need more
speeds than the equivalent gasoline car. That's one of the reasons
trucks typically have 18 speeds or more. That's overkill for a car, but
a 6 speed gearbox would not be out of line.
The reasons diesels have gone out of favour in cars is more than that.
Firstly, diesel fuel used to be much cheaper than gasoline. That
changed a few years after diesel cars came out. Secondly, diesel fuel
is more dirty when it burns than gasoline. This produces problems with
pollution requirements, and is also an aesthetic issue as drivers
contend with nasty black sooty deposits on their cars. I think these
are the main reasons why diesels went out of favour. Diesels
traditionally are harder to start in cold weather than gasoline --
supposedly the newer automotive units have fixed this, but I wonder how
well they age. Diesel fuel is also harder to get -- it's easy to get
along expressways, but it's not necessarily at the corner gas pump in
town.
|
gull
|
|
response 123 of 184:
|
Mar 2 04:24 UTC 2002 |
Hard winter starting on modern diesels is mostly a matter of glow plug
maintenance. If you have a bad plug, you'll never get that cylinder to
fire on a cold day. Leaky injectors will burn out glow plugs in no
time -- the constant drip of fuel kills them off somehow.
Diesel cars are popular in Europe, where fuel is expensive. They
aren't so popular here. Partly this is because Americans are fixated
on cars that are powerful and quiet, and diesels aren't really either.
I have no idea what the diesel Escort's reputation is; I didn't even
know they made one. In general I'd be suspicious of a small diesel
made by a U.S. car company because I don't feel they have the
experience to really do it well. Volkswagen has made some really
excellent small diesels, though.
|
other
|
|
response 124 of 184:
|
Mar 2 21:16 UTC 2002 |
Also, if you run a diesel out of fuel, it is a major deal to get it going
again. You can't just pour in more fuel like you can with a gas engine.
At least, that's the way it used to be...
|
russ
|
|
response 125 of 184:
|
Mar 2 22:17 UTC 2002 |
Re #123: Ford did not build the engine for the Escort diesel. I
believe it was Japanese.
Re #122: The Buick diesel was a prechamber design, not direct
injection; this speeds ignition and combustion at the cost of greater
heat loss. This qualified it as a high-speed diesel. Such engines
do not need the huge number of speeds required of semi tractors and
their medium-speed, direct-injected engines. (Typical power band on
a semi is 1600 to 2500 RPM; that goes all the way from maximum torque
to redline. When your usable range is about 1.5:1, you're going to
need lots of gears to keep the engine running there over road speed.)
One of the biggest problems with the Buick diesel was lack of fuel
conditioning. A little bit of water or paraffin in the fuel, and
the engine would quit when the temperature dropped. The engine was
introduced on the verge of a winter when fuel supplies were running
short and refiners and distributors were pumping the sludge out of
the bottom of their tanks; without water traps and fuel heaters, the
Buick was doomed.
Modern common-rail diesel fuel systems have beaten the diesel clatter
problem as well as the smoke. I've driven a turbodiesel Focus; it's
a lively, torquey little beast, and quiet too.
|
gull
|
|
response 126 of 184:
|
Mar 3 05:53 UTC 2002 |
Re #124: That isn't quite the big deal it used to be. Even on my
friend's 1980 VW Dasher Diesel it wasn't a catastrophe, it just took a
lot of cranking. The only fuel pump was a vane pump in the injector
pump, and you had to crank until it pulled fuel all the way from the
tank.
That car had acceptable performance with just a four-speed,
incidentally. It wasn't exactly peppy, but it did okay. This was
before VW started turbocharging their diesels; the turbo makes a huge
difference in power. Without the turbo the little diesel (I think it
was 1.6L) only cranked out 49 horsepower.
Re #125: The newest VW turbodiesels are surprisingly quiet, too.
There's a bit of clatter, more than a gas engine, but it's not
objectionable. The most obvious sign a new Jetta TDI is a diesel,
other than the exhaust odor, is the turbo whine.
|
jaklumen
|
|
response 127 of 184:
|
Mar 3 06:02 UTC 2002 |
resp:122 (First sentence) No, not according to a mechanic friend of
mine.. and he drives a particular car that proves it. Your next
sentence seems about right-- GM shot themselves in the foot by
producing diesel engines that were shoddy. The car he drives was a
diesel produced in 1985, and it is excellent for gas mileage. Because
GM produced some really crappy diesel engines in the 1980's save a
few, including the one just mentioned, diesel was disfavored in the US.
I am going to have to talk to him specifically, because although many
of you are quite well-informed, I'm not convinced you know completely
what you're talking about. The way he explained it to me was this
(and I'm sure I will forget a LOT): Basically, a diesel is a long-
stroke engine. Any engine that is long-stroke, and you can make
unleaded long-stroke engines, has better fuel economy. It is adequate
for most typical driving.
-However- the world of racing has a STRONG influence on the world of
cars, and so there has been strong emphasis on performance,
particularly quick acceleration, etc.
I asked him about diesel prices vs. unleaded-- he said something about
that diesel was cheaper than unleaded, and would remain cheaper if the
price wasn't set artifically higher by.. the government, I believe.
hold your offenses until I talk to him.. I've listened to him a lot
concerning car mechanics and history of such, and rarely can I
remember it all to any good effect.
|
gelinas
|
|
response 128 of 184:
|
Mar 3 07:00 UTC 2002 |
Last I heard, in Michigan anyway, gas taxes are higher than diesel taxes.
This has been a sore point for a while: Diesel is primarily purchased by
commercial ventures, who (seem to) have more clout in the legislature. So
they avoided the road-improvement increases the rest of us have had to
swallow.
A few months back, I bought gas from a place that had an interesting sticker
on its pumps: "Price includes $0.33 in taxes." At a time when gas was
selling for $1.20 or so. (87 octane unleaded.)
|
gull
|
|
response 129 of 184:
|
Mar 3 17:59 UTC 2002 |
Gas taxes are equal to diesel taxes, unless you're a semi truck
driver. Then you get the "three axle discount" and save about 15(?)
cents a gallon. Note that the price advertised by truck stops is
usually the three-axle discount price.
As far as #127, you're probably right about the influence of racing on
cars. I'm not sure about the efficiency of a long-stroke vs. a short-
stroke engine, but I can think of some reasons why that might be true.
A big reason diesels are more efficient, though, is that they're
unthrottled engines. A gasoline engine, unless it's at full throttle,
is always having to work to pull air past a partly-closed throttle
plate, and that robs some efficiency. Diesels have no throttle plate,
so the intake is much less restricted.
Why not have your friend look over the Escort you're thinking of
buying? He sounds knowledgable about these things.
|
mdw
|
|
response 130 of 184:
|
Mar 4 02:41 UTC 2002 |
"Long-stroke" seems to be another name for "under-square", which is just
a fancy way of saying the stroke is larger than the bore. The other
extreme is "over-square" or "short stroke" which means the bore is
larger than the stroke. Neither of these has any direct relationship to
either economy or performance. Mostly it has to do with materials and
stress. The more under-square it is, the more stress the piston is
under, and hence, the harder it is to make one that's strong enough.
The more long-stroke it is, the larger the crank case has to be, and the
higher the piston speeds goes, which affects lubrication and longevity.
Diesels tend to be longer stroke due to higher compression ratios which
result in more piston stress. Gasoline engines tend to be generally
slightly under-square, because they put less stress on the piston, and
it's more important to conserve on engine size. All things being equal,
an under-square engine can rev higher, which means gasoline engines
generally enjoy a distinct HP/weight advantage over diesel. This gives
gasoline powered vehicles a potential mpg advantage in start-stop
traffic over diesel. On the other hand, diesel fuel contains about 8%
more energy per gallon than gasoline, giving them an inherent "mpg"
advantage, especially in highway driving where weight doesn't matter
nearly as much as wind resistance.
A lot of people make a big deal over "torque" instead of "HP". Torque x
rpm = HP. Tranmissions have gearing in them, which means they can
adjust rpm, and hence also torque. If you have a high reving engine
that produces lower torque, you can compensate by putting a larger gear
ratio in. What you really care about is the "HP", the shape of the
power band, and the ratio between its lower & upper edge. Large
motorcycle engines produces about as much if not more power than small
truck engines. You'd need more gearing, because truck engines don't
usually go > 2000 rpm, and many motorcycle engines go to 8K-10K+. You
could get by with fewer gears, because the truck has a 1:2 useful ratio
in its power band, and the motorcycle has a 1:5 useful ratio. On the
other hand, the motorcycle engine will be less economical to operate,
and will wear out long before the truck engine does.
You can read more about bore & stroke here:
http://www.g-speed.com/pbh/bore-vs-stroke.html
http://www.howstuffworks.com/
and fuels here:
http://www.osc.edu/research/pcrm/emissions/petrol.shtml
|
drew
|
|
response 131 of 184:
|
Mar 5 06:56 UTC 2002 |
Re #129:
The person with the mechanic friend (Captain Lumen) and the person
considering the diesel Escort (myself) are two different people. Though I
would love to have him look at the car.
|
jaklumen
|
|
response 132 of 184:
|
Mar 5 07:20 UTC 2002 |
it would be fun, and a hell of an adventure. Ben is closer in Moscow,
ID, but alas, is far, far busier than even I.
|
other
|
|
response 133 of 184:
|
Mar 5 14:50 UTC 2002 |
I have a friend who lives in Moscow, ID.
|
gull
|
|
response 134 of 184:
|
Mar 5 15:09 UTC 2002 |
Re #131: Ah, sorry. I lost track.
It'd be good to have a knowledgable diesel mechanic look it over.
Among other things, a compression test would be nice. (The tool to do
it is much more expensive than the one for gasoline engines.) Low
compression on a diesel results in very sooty exhaust, hard starting,
and poor fuel economy.
|
drew
|
|
response 135 of 184:
|
Mar 5 17:56 UTC 2002 |
I'll see what I can do about it.
Still, how good *are* the diesels in Escorts specifically?
|
russ
|
|
response 136 of 184:
|
Mar 6 00:33 UTC 2002 |
Re #130: Under-square engines can generate more power for several reasons:
1.) They have a larger cylinder head, which means more area for
valves. Larger valves means freer breathing; more air charge
gets into the cylinder, and exhaust back pressure is smaller.
2.) The smaller stroke means lower piston speeds and accelerations,
allowing higher RPMs.
This has relatively little to do with efficiency at cruise, which
is almost always done well below redline RPM except for such vehicles
as semi trucks where that pesky 1.5:1 power band must be respected.
One of the influential factors for efficiency is, believe it or not,
length of the connecting rod. The longer the con rod is, the smaller
the angle it makes with respect to the line between the crankshaft
center and the bore center. This decreases the side forces on the
piston, which in turn reduces frictional losses from the piston
riding against the side of the cylinder. Every bit of power that
is reclaimed from friction goes straight to the output shaft.
|
hash
|
|
response 137 of 184:
|
Mar 6 03:45 UTC 2002 |
I had a diesel tempo. It ran great. it ran awesomely. but, for some odd
reason we couldn't get it to start. figured out what it was, but I can't
remember now. otherwise, it was a most excellent engine. the car was rusted
out and the interior was rotting away, but it was great under the hood. minus
that it stopped starting. but, once you got it started it purred like a
kitten and sipped fuel.
|
jep
|
|
response 138 of 184:
|
Mar 6 04:22 UTC 2002 |
A car that runs great but can't be started is known as "disposable".
|
gull
|
|
response 139 of 184:
|
Mar 6 14:37 UTC 2002 |
I'd suspect the glow plugs. They do eventually wear out, and a diesel
with one or two bad ones is hell to start, especially in cold weather.
|
keesan
|
|
response 140 of 184:
|
Mar 6 15:16 UTC 2002 |
Re 138 - A lot of people with lots of disposable income think that way. Other
people fix things that are not working perfectly and get a lot more use out
of them.
|
jmsaul
|
|
response 141 of 184:
|
Mar 6 15:28 UTC 2002 |
Sure, but you wouldn't be able to do that if the first kind of people didn't
throw them away for you to salvage.
|
rcurl
|
|
response 142 of 184:
|
Mar 6 15:47 UTC 2002 |
You *can* fix your own stuff, and not add it to the "disposable" collection.
|
jmsaul
|
|
response 143 of 184:
|
Mar 6 16:20 UTC 2002 |
That isn't what Sindi and Jim do, though. They pick up stuff other people
have gotten rid of, which requires people willing to get rid of stuff. (I'm
not criticizing what they do, by the way -- I respect that aspect of their
lifestyle a lot, even though it isn't the way I want to live.)
|
keesan
|
|
response 144 of 184:
|
Mar 6 16:55 UTC 2002 |
Jim also fixes a washing machine which he purchased new (about 25 years back).
|
jep
|
|
response 145 of 184:
|
Mar 6 18:14 UTC 2002 |
I respect what Jim and Sindi do with used electronics and such as
well. I got a real nice stereo from them for not very much money, also
a VCR.
In #138 I was referring to a car which couldn't be fixed. I've had
cars like that, and had them when I didn't have much money. It's a
tough situation, but that doesn't change the basic fact. If the car
can't be fixed, it's disposable and you have to get another.
|
keesan
|
|
response 146 of 184:
|
Mar 6 18:26 UTC 2002 |
Just because something does not start does not mean you cannot fix it.
That is probably minor compared to the body being rusted out.
|