Volkswagen’s turbocharged direct injection (TDI) clean diesel engine offers high mileage between fill-ups and more than 50% better fuel economy than similarly sized petrol engines. With a potential 43 highway miles per gallon, you can get up to 795 miles per tank, in a car that emits lower CO2 commissions than 93% of other vehicles. TDI is available in newer Volkswagen cars such as the Passat, Golf, Jetta sedan and Sport Wagon, Beetle and Beetle Convertible, and Toureg.
To keep your TDI running at peak performance, it’s important to understand how it works and how to maintain it.
What makes a TDI engine different
The secret to TDI’s success lies in the engineering. Replacing the indirect injection of older diesel models, the new models use a fuel injection system that sprays atomized fuel directly into the main combustion chambers and not the pre-combustion chambers. This process is combined with forced induction with the turbocharger which increases the amount of air passed into the engine’s cylinders and an intercooler to reduce the temperature and density of the turbo charge air.
The result for you, the buyer? More fuel is injected and burned, so you’ll notice increased engine efficiency and increased power, along with more torque and lower emissions.
Fuel Requirements for TDI
The Volkswagen TDI engine runs on diesel fuel (petro diesel) or certain types of biodiesel fuels. The downside of the engine’s technical prowess is that it’s picky about the kind of fuel it needs. In the US, VW recommends No. 2 diesel fuel, which has a higher cetane number than No. 1 fuel and a lower viscosity. Proper fuel straight from the pump is common in Europe, but some American drivers must use additives or premium diesel to ensure correct cetane levels.
“Misfeeding” your TDI engine with regular gasoline instead of diesel can be a costly mistake. Some older VW models were more forgiving, but putting the wrong fuel in a modern TDI engine will damage the fuel pump and ruin the engine when the fuel goes through the fuel system. That system on 2013 vehicles has been redesigned with a fuel tank flap to prevent you from inserting a gas nozzle instead of a diesel nozzle into the tank.
The cost of an accidental incorrect refueling can range from $100 or so to pump the wrong fuel and replace the filters to over $8,000 to replace the entire fuel system. Most of these repairs are not covered under warranty.
What can you diagnose yourself?
Your local VW dealer has a great service department that can keep your TDI engine running strong. Regular maintenance costs are similar to professional service for a gas-powered VW. However, if you’re a competent backyard mechanic who enjoys doing your own car repairs, there are a few situations unique to a TDI that you can diagnose yourself:
- If you hear noises, are they “normal” for your TDI engine? Most drivers notice a clicking noise from the steering column, a clicking noise from the EGR and pressure control valves, and a clicking noise from the shoulder valve when shutting off the engine. These noises indicate proper performance, not a problem, but as a new TDI owner, you need to learn what to ignore and what to pay attention to.
- Engine won’t start or won’t start? While the car is in neutral, turn the ignition to the run position to see if you get a check engine warning or glow plug lights. If not, you may need a new battery as the motor is not receiving power.
- Does the engine start? If you see check engine or glow plug lights on the dash, but the car makes noise when you try to start, it may be low on fuel, corroded cables leading to the battery, or loose connections.
- Do you get a “relay 109” fault? If the check engine light or glow plug goes on and off, you may have a relay 109 fault that requires replacing the relay. If that doesn’t work? You may have a faulty ignition switch or security system. You may also see the glow plug light if you have a burned out brake light.
- Does your engine smoke when fully revved after a fill up? You may have received a poor quality fuel tank.
A Volkswagen TDI engine offers the best in performance and efficiency, but they are particular engines that require very specific maintenance and repairs. Always remember to replace faulty parts with genuine Volkswagen replacement parts, or choose your local VW service department for professional service from experienced, certified mechanics.