Diesel Power
Mobile Icon BtnMobile Icon Btn RO
Newsletter

11 Diesel Myths Busted!

Clearing-Up Diesel Misinformation

Text By , Photography by Diesel Power Archives

1.Ford Owns Cummins
This is something we hear misinformed enthusiasts claim all the time - and it's completely untrue. More than two decades ago, Ford held roughly a 10 percent share of Cummins' stock. As a shareholder, Ford earned a seat on Cummins' board of directors, but that was the extent of it's influence or control over Cummins. In 1997, Ford divested itself of all Cummins stock. For the record, you can order a Ford with a factory Cummins option - but it's only available in a medium-duty F-560 or F-750.

2. Isuzu Builds the Duramax
Yes and no. The 6.6L Duramax (produced at DMAX Ltd., in Moraine, Ohio) was a joint venture, formed in the late ’90s by General Motors and Isuzu. Originally, Isuzu was the majority owner, with a 60 percent share (vs. GM’s 40 percent), but less than a year after the DMAX partnership was formed, GM raised its stake to 49 percent. Today, the original numbers are reversed, with GM now the 60/40 majority owner. Isuzu was responsible for the base engine’s design and validation, while GM was tasked with creating the installation and packaging within its vehicles. Isuzu and GM collaborated on the original engine calibration work.

3. Diesels Get 20+ mpg While Towing
Inflated mpg claims while towing are hard to swallow, and they only hurt diesel’s reputation. Our first question, knowing that most trucks are equipped with programmers or larger-than-stock tires (which often throw off a truck’s mileage readout), is always whether or not those numbers were hand-calculated. While 15, and even 16 mpg is believable (and easily outperforms gas-powered trucks in the same vehicle class), that’s on the high end of what any diesel owner should expect to see—unless you’re towing at 30 mph. Why is this myth so harmful? Because a novice will end up purchasing a diesel truck expecting to get outstanding fuel economy while towing. Then, when 15 mpg is realized, it’s nowhere near the 25 mpg they were told they’d see. There are simply too many factors working against a diesel truck with a trailer in tow to see 20-plus-mpg towing (wind, poor aerodynamics, weight, engine load, elevation, rolling resistance).

4. Diesels Never Start Easy in Winter
This is one we fundamentally disagree with. While diesels may never start as easily in frigid conditions as their gas counterparts, most modern diesel vehicles come with block heaters. Some folks either don’t know, or don’t take the time to utilize this in cold weather—although it’s highly recommended. However, our ’02 Dodge 3500 sits outside year-round and starts up just fine without the block heater—and in 10-degree weather. The key to keeping older diesels starting in cold conditions is to make sure the intake grid heater is functioning properly, the batteries are healthy, and the glow plugs and glow plug relay are up to snuff.

5. If a Turbo is Laggy, it’s Better
While big single turbochargers can make great power and excel in competition, a small turbo (or rather, a correctly sized turbo) is much better for the kind of driving most of us do: daily commuting or towing. Under throttle, sure, a large single will pin you back in the seat, but at low rpm, you sacrifice some of the torque needed to get loads moving, and in Overdrive you can risk surging and even permanently damaging the turbo. That being said, when you get away from traditional, fixed- geometry turbos, there is an exception to the rule. Larger variable-geometry turbos don’t always hurt driveability and hardly yield any increased turbo lag, especially when it’s a stock VGT that’s fitted with a larger compressor wheel.

6. Kerosene is a Good Way to Keep Fuel from Gelling Up
Wrong. It can help, but it will require adding more than just a couple quarts to your tank to make any difference. For instance, a minimum blend of 30 percent kerosene (70 percent diesel) is needed to reduce your fuel’s pour point by just 15 degrees. As you can imagine, this will get expensive, fast. Not only that, kerosene doesn’t help much in preventing fuel line freeze-ups; it lowers the cetane rating of your diesel fuel (less BTUs means less energy and lower fuel economy), and it decreases its lubricity. If you want to keep your fuel from gelling up, look into additives specifically formulated to reduce gelling, such as Power Service Diesel 911 or Diesel Recovery from Amsoil.

7. Biodiesel and Vegetable Oils Are the Same
A lot of folks believe these two fuels are similar—but they aren’t. First and foremost, a straight mix of either shouldn’t be run through a factory fuel system (biodiesel is too much of a solvent and too viscous, and vegetable oil is too viscous and corrosive). While a biodiesel blend is now present in most conventional diesel fuel at the pump, less than 20 percent can be found in it (hence the B20 compatibility ratings currently offered by the Big Three). Biodiesel can be made from vegetable oil and animal fats but can also come from natural materials such as soy, sunflower, and algae, to name a few. Vegetable oil is best known as waste cooking oil (or grease), and due to its thick viscosity and corrosive nature, it typically requires things like an upgraded lift pump, fuel filter, and fuel lines, not to mention the need to preheat it before sending it through your engine.

8. Diesels Are Dirty and Loud
Despite increased sales numbers in both cars and trucks, much of the general public still believes diesels are smoke-belching, noisy, rattle boxes. While earlier direct injection diesels were noticeably audible, common-rail technology has made them almost as quiet as gas engines. On the smoke front, once the EPA stepped in, manufacturers had to make diesel vehicles cleaner and cleaner in order to legally sell them in America. Today, diesel cars and trucks are squeaky clean at the tailpipe and emit less NOx and particulate matter thanks to EGR (exhaust gas recirculation), DPFs (diesel particulate filters), and SCR (selective catalytic reduction, or urea injection).

9. Propane is Like Nitrous for Diesels
This is one we’d like to put to bed—once and for all. A lot of hot-rodders (many who don’t even own diesels) believe this to be true. It is not. In fact, they’re polar opposites. Although both propane and nitrous are gases, in an engine, propane is like burning another fuel, while nitrous is like adding another turbo (thanks to its oxygen content). For daily driving, propane injection can improve fuel economy and provide a small bump in power. It’s best in unmodified engines, but when used for all-out horsepower gains, it can begin to ignite prematurely in the cylinder (leading to excess heat, which can cause melted or holed pistons, or corroded injector nozzles). Propane can become dangerous to an engine because there is no way to control its ignition point. Its delivery can’t be metered as precisely as the fuel delivery from an injector. Nitrous, on the other hand, is for competition and can literally add hundreds of horsepower. It’s best used at high boost and high rpm (injecting nitrous at low boost levels can cause severe engine damage).

10. Diesels are More Expensive to Maintain and Repair
In the age of high diesel prices and strict emissions, we can see how this argument has picked up steam—but it’s still not true. If you’re a bigger picture person and plan to keep your truck for the long haul, you know this myth is bogus. One of diesel’s primary benefits has always been longevity. Over the life of a 300,000-mile engine, you might need a set of injectors, a lift pump, or even an injection pump, but properly maintained diesel engines rarely experience catastrophic hard-part failures and still get better fuel economy (especially when towing) than the gas competition. Diesel oil changes can be pricey, but 7,500 to 10,000 (or more) miles are widely accepted change intervals for newer diesels.

11. Correction Factors for Diesel and Gas Engines are the Same
This is false based on the simple fact that most diesel engines are turbocharged. Turbochargers make boost, which is the amount of intake manifold pressure that exceeds atmospheric pressure (14.7 psi at sea level). Correction factors (say, on a chassis dyno) are used to show how much power a vehicle would make if it were at sea level. Correction factors are much lower for turbocharged engines than for non-turbo versions, and the higher the boost, the lower the correction factor. Using a theoretical performance comparison that takes elevation into account, air pressure drops roughly 1 psi for every 2,000 feet of elevation. At 6,000 feet, a gas engine has 11.7 psi of air pressure (vs. 14.7 at sea level), and will, in theory, be making 80 percent of its sea level power. A diesel at the same elevation, operating at a peak boost of 20 psi, will be (once again, in theory) making 91 percent of its sea level power.

Enjoyed this Post? Subscribe to our RSS Feed, or use your favorite social media to recommend us to friends and colleagues!
0 comments
Diesel Power