Exposing some of the misconceptions and outright lies about today’s
diesel engines.
By C.J. Baker
Today’s diesel engines
are saddled with a lot of myths and misinformation. In all fairness, some of the bad
rap was justly deserved in recent years, but the new generation of clean turbo-diesel
engines for light trucks and motorhomes bears little in common with those of just a
few years ago – it’s not your Granddaddy’s diesel anymore!
Clean diesel technology
may well win out over alternative fuel vehicles, such as those that use compressed natural
gas (CNG), hybrid, or even fuel cell technologies. Clean diesel designs will cost less
to produce and buy, operate more cost effectively, and won’t require a completely
new fueling infrastructure. The World Wide Web offers a wealth of information on this
topic. Just use the search words, “clean diesel”. Does this mean everyone
will drive diesels? Hardly, but the acceptance of diesels will increase to the point
that light duty diesels may account for over 15 percent of the vehicles on the roads
of America. In western Europe, diesels now make up 30+ percent of the vehicle population,
with some experts predicting the percentage may rise as high as 50 percent in the next
few years. Tax incentives for diesel-powered vehicles would hasten acceptance here,
as they did in Europe. Clean, modern diesel technology could change the negative aura
surrounding SUVs, for example.
Some old perceptions about
diesels will die hard, especially in a country where gasoline has always been relatively
inexpensive. Forward thinking people, however, have been quick to see the economic advantages
of diesels, particularly in relation to our growing dependence on foreign oil and the
instability of the world oil market. The potential 40+ percent fuel economy increase
from diesels is hard to ignore. In response, diesel engineers have made huge progress
in eliminating the problems associated with diesels. Here are examples:
MYTH
#1
Diesel engines are smoky and dirty.
FACT
Diesel smoke is comprised of soot from unburned or partially burned fuel. Modern computerized
fuel control and management coupled with ultra-high-pressure common rail fuel injection
have virtually eliminated diesel smoke. What little smoke remains is nearly invisible,
and even that trace smoke will be gone when the petroleum industry switches over to
ultra low sulfur fuel, as mandated by the EPA by 2006. As for dirty, no smoke means
no soot, and no soot means no dirt.
MYTH
#2
Diesel exhaust smells bad.
FACT
The smell associated with diesel engines in the past came from incomplete combustion,
smoke, and high sulfur content in diesel fuel. As mentioned above, electronic fuel management
has dramatically improved combustion and nearly eliminated smoke. Today’s diesels
won’t offend most folks, and when the sulfur goes, even those people with sensitive
noses will be hard pressed to honestly object.
MYTH
#3
Diesels have to be noisy, especially at idle.
FACT
There used to be a lot of truth to this statement, but new diesels with a feature called
“pilot injection” have virtually eliminated the clattering sound associated
with diesel engines. Many of these diesels are so quiet that it takes an educated ear
to recognize that the engine is a diesel when it goes by or is stopped at a stoplight.
Unfortunately, there are enough noisy older diesels on the road to sustain this myth
for some time.
MYTH
#4
Diesel are slow and sluggish.
FACT
All new automotive, light truck and motorhome diesel engines sold in America today are
turbocharged. These turbo-diesels are responsive and powerful. They are capable of accelerating
quickly, and they have high-torque output for climbing grades or sustained high-speed
operation. Today’s turbo-diesels also are responsive to performance upgrades that
make their performance nothing short of incredible. (see ”Project
Sidewinder Goes to the Salt”)
The following are a few
additional “tall tales” that occasionally arise:
MYTH
#5
You should occasionally mix a gallon of gasoline with a tankful of diesel fuel to clean
the fuel injectors and remove carbon from the cylinders.
FACT
Don’t do it! Gasoline, even in low concentrations, destroys the lubricity of diesel
fuel and can quickly destroy the diesel’s expensive fuel injection pump. Gas in
diesel fuel also increases the combustion temperature and can actually damage the expensive
fuel injection nozzles. And lastly, today’s diesel fuel does not gum up fuel injectors,
or build carbon deposit in the cylinders as was sometimes the case many years ago.
Don’t ever mix gasoline, or alcohol, with diesel fuel.
MYTH
#6
You have to go to a truck stop to buy diesel fuel.
FACT
With the popularity of diesel pickup trucks and SUVs, more and more gasoline stations
are now adding diesel fuel pumps. This trend will continue as diesel popularity grows.
But, yes, you can buy diesel fuel at a truck stop if want to, and besides, you can buy
great country music CDs while you’re there!
MYTH
#7
You have to let a turbo-diesel idle for two minutes before you shut it off.
FACT
This is a current myth that has a basis of fact stemming from
many years ago. It also has a kernel of truth regarding
today’s turbocharged gasoline engines that operate
at higher peak exhaust temperatures than turbo-diesels.
In the early days of turbochargers,
the turbo shaft was supported by a babbitt bearing that could
seize, or even melt, if the engine was shut off immediately
after sustained boost conditions where the turbocharger
would “heat soak”. A two minute cool down at idle
allowed the turbocharger to dissipate any remaining spinning
inertia, and the oil circulation cooled the bearing
and prevented oil “coking” in the bearing area. Turbochargers
haven’t
used babbitt bearings for over 30 years, and today’s oils
resist coking. Synthetic oils won’t coke, period. With
a turbocharged gas engine, it’s still good insurance
to let the engine idle for 30 seconds to a minute to allow
the turbo or turbos to dissipate any inertia and to cool
the bearing area to prevent oil coking, especially if the engine
has been worked hard just prior to shut-down. Of course, using
quality synthetic oil eliminates this potential coking problem.
Today’s turbo-diesels are a different story. There is
really no reason to “cool
down” a turbo-diesel these days, but you won’t hurt
anything by doing it either. You can still find people who
swear you have to do it, but the myth is fading. Maybe
they just like to sit and listen to the radio.
MYTH
#8
You can’t use synthetic oil in a diesel.
FACT
Synthetic oils can be, and are, used in many diesel engines. Every engine manufacturer
has specific oil recommendations, and as long as the synthetic oil meets the API rating
recommended for that engine, it is acceptable. For most light-duty truck diesels, this
means a minimum of API CF or CD. Some folks think synthetic oils will void the warranty
on a turbo-diesel, but again, if the oil has the correct API rating, no problem. If
you’re still in doubt, read your manufacturer’s warranty. It’s a contract
between you and the manufacturer.
MYTH
#9
Diesel fuel has less heat energy than gasoline.
FACT
Diesel fuel has almost 11 percent more heat energy than gasoline. A typical gallon of
gasoline has about 124,800 BTU, whereas a typical gallon of #2 diesel has about 138,700
BTU.
MYTH
#10
Diesels are hard to start in cold weather.
FACT
Diesel fuel is less volatile than gasoline, and wax crystals can begin to form in diesel
fuel at lower temperatures, so it’s true that many diesels have starting problems
in cold weather (below freezing temperatures). Happily, modern diesels with common rail
injection and pilot injection have starting capabilities equal to gasoline engines at
temperatures as cold as -40º F. Many diesels also feature fuel heaters to prevent wax
crystal formation. The use of synthetic oils also helps diesels crank over in cold weather.
This is just one more area where diesels have changed for the better.
MYTH
#11
A diesel engine will run under water.
FACT
This isn’t completely a myth. Like any internal combustion engine, a diesel needs
access to fresh air in order to run. It must also have water-free fuel and be able to
easily expel exhaust gases. If these conditions are met, technically a diesel could
run under water, assuming its fuel management computer and wiring harness is watertight,
and some military vehicles with raised air intakes and exhausts can run under shallow
water. On the other hand, it’s probably not a good idea to drive your diesel pickup
through a river, pond, lake, creek, or the municipal swimming pool no matter how logical
the idea seems at the time!
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