For as long as diesel engined cars have been sold in the US, myths about them have existed. Some are loosely based in facts, some are simply not true.
One I recall from when TDIs were launched here was dealers telling potential customers that opening the driver’s door on a TDI activated the glow plugs.
As time has passed, new myths have surfaced that are more relevant to the diesels we have on the road today. Here are 7 common ones, along with the facts that refute them.
MYTH #1
Deleted cars need less maintenance
It’s true that when you remove hardware from a car you’re saved the worry of that hardware failing. Clearly this is the case with DPFs and sensors that are no longer needed on a deleted diesel.
However, routine maintenance requirements don’t change. Filters and fluids should be serviced on the same schedule, along with timing belts, if the car has one. And of course any non-engine related maintenance doesn’t change.
MYTH #2
White smoke on startup is a sign of a failing turbo
Short answer: It depends. Oil can accumulate in a failing turbo and that will cause white smoke on start up. However, smoke can come from many other sources. White smoke can be the result of unburned fuel. A malfunctioning injector or glow plugs that aren’t working can cause white smoke on startup.
A common cause of white smoke on older TDIs is worn valve guides and seals. When the car sits and cools off, oil can flow from under the valve cover into the combustion chamber, and it burns on startup, emitting white smoke.
Issues with crankcase ventilation can also cause smoke. If your PCV system is pushing extra oil into the intercooler piping, the engine will smoke as it burns that off after startup and any boost request.
MYTH #3
Diesel Additives are a waste of money
Many diesels have long service lives without the owner using additives. However, the diesel supply in the US is notoriously poor quality. Recently we’ve heard reports suggesting that delivery companies are not dosing tank trucks with additives before deliveries. And it’s not uncommon for people in colder climates to have issues with fuel gelling, even with winter fuel.
The real benefit of fuel additives is in the longevity of your diesel’s fuel system. That’s where it’s worth protecting your investment.
MYTH #4
It’s better to have a common rail diesel that doesn’t require Adblue
We’re not sure why people don’t like Adblue. It allows manufacturers to tune diesels for better performance and economy, using Adblue to make sure the emissions system performs correctly. For example, 2015 4 cylinder VW TDIs achieve significantly better fuel economy than the ’09-14 cars that preceded them. And their emissions system is simpler overall, using fewer sensors, for example, than the ’15 MY cars.
Adblue is cheap. And although people do have issues with pump heaters and injectors, we see it as a net positive.
MYTH #5
All CP4 pumps fail
CP4 pumps get a bad rep. Yes, some fail, but CP3 pumps fail, too. According to VW data, the percentage of CP4 pumps that failed during the warranty period is in the low single digits. Many of these pumps have performed for hundreds of thousands of miles without issue. If you want to be sure your CP4 pump lasts, see #3 above.
MYTH #6
VW PD injectors never wear out
PD injectors are remarkably durable. But they will eventually wear out. How long they last depends at least in part on fuel quality, but beyond about 300K miles, they may be due for a refresh or replacement. Still, that’s pretty amazing.
MYTH #7
Big fuel is the only path to big power
Decades ago, adding fuel was about the only way you could increase power in a diesel, especially a normally aspirated (non turbo) one. Owners liked to make changes to the injection pumps in Cummins 12 valve diesels, and people wrote articles (that were printed in magazines back then) about turning up the fueling in your Mercedes diesel.
It still holds true that more fuel is necessary. But increasing fuel is much more sophisticated now. Tunes have multiple “maps” for fueling, injectors have multiple injection events that can be managed throughout the compression stroke, and fueling can be coordinated with boost and timing to keep heat and emissions down while maximizing power output.
So fuel is still a path, it’s just not the only one.
Conclusion
There are other myths out there, and you may have experienced some of them yourself. These are just a few.