Turbo-Diesel Fact & Fiction

Exposing some of the misconceptions and outright lies about today’s diesel engines.

Diesel are slow and sluggish.

The Banks Project Sidewinder ran 222.139 MPH powered by a modified 2003 Cummins diesel engine, and it did it without leaving a trail of smoke

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:



Diesel engines are smoky and dirty.



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.



Diesel exhaust smells bad.



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.



Diesels have to be noisy, especially at idle.



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.



Diesel are slow and sluggish.



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 Dakota Goes to the Salt“)

The following are a few additional “tall tales” that occasionally arise:



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.


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.



You have to go to a truck stop to buy diesel fuel.



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!



You have to let a turbo-diesel idle for two minutes before you shut it off.



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.



You can’t use synthetic oil in a diesel.



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.



Diesel fuel has less heat energy than gasoline.



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.



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.



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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