Technician Inside Info: SEAT Leon 2.0 TDI (2018)

A technician's honest look at the 2018 Leon 2.0 TDI — and why oil consumption and repeated DPF regenerations are so often two sides of the same problem.

Technician Overview

The 2018 SEAT Leon 2.0 TDI can be a very good all-round car. It is quick enough, economical on a run and shares a lot of its mechanical parts with other Volkswagen Group cars, so parts and specialist knowledge are widely available.

From a technician's point of view, the two concerns we would pay particular attention to are oil consumption and cars that seem to regenerate the diesel particulate filter too often.

That does not mean every Leon 2.0 TDI will suffer from these problems. Maintenance, mileage and the type of journeys the car has done make a massive difference. The important thing is recognising the warning signs before buying rather than assuming a warning light just needs clearing.

Oil Consumption or Burning Oil

Some 2.0 TDI Leons can use oil between services. A small amount of oil use is not automatically a fault, but regular top-ups, visible smoke or an owner carrying oil in the boot need investigating properly.

The first job is to establish where the oil is going. Oil loss can come from an external leak, the turbocharger, the crankcase-breather system or internal engine wear. A light coating of oil inside diesel boost pipes is normal; a large quantity collecting in the pipework or intercooler is not.

Warning Signs

• The oil level is below minimum or barely touching the dipstick.
• The seller says it “uses a bit” but cannot tell you how much.
• Bottles of engine oil are stored in the boot.
• Blue smoke appears on cold start, after idling or under acceleration.
• There is a burning-oil smell after the road test.
• Oil is leaking around the engine, turbocharger or undertray.
• The service history shows long gaps or the wrong oil specification.

Oil consumption matters on a diesel with a DPF because burned engine oil leaves ash behind. Unlike soot, that ash cannot simply be removed during a regeneration. Over time, it reduces the DPF's usable capacity and can cause regenerations to become more frequent.

Repeated DPF Regenerations

The DPF traps soot from the exhaust. When the calculated soot level reaches a set point, the engine management system raises exhaust temperature and burns that soot away. This is an active regeneration.

Regeneration itself is normal. The concern is when the vehicle seems to be regenerating repeatedly, struggles to complete one or brings on the DPF or engine-management warning light.

Short journeys are a common cause, but they are not the only cause. A DPF that keeps loading up can also be the result of an underlying engine or sensor problem.

Possible Causes of Repeated Regeneration

• Regular short journeys and interrupted regeneration cycles.
• Excessive oil consumption adding non-combustible ash to the DPF.
• An inaccurate DPF differential-pressure sensor or restricted sensor pipes.
• Faulty exhaust-gas temperature sensors.
• EGR-system faults affecting combustion and soot production.
• A thermostat fault preventing the engine from reaching the correct operating temperature.
• Injector or air-intake faults causing the engine to produce excessive soot.
• A DPF with high ash loading due to age and mileage.

Signs the Car May Be Regenerating

• Idle speed sits higher than normal.
• The cooling fans continue running after the engine is switched off.
• Stop-start becomes temporarily unavailable.
• Fuel economy drops.
• The exhaust smells hotter or stronger than usual.
• The engine note changes slightly and the car feels different at low speed.

One regeneration during a test drive does not prove there is a fault. However, evidence of very short intervals between regenerations needs further investigation.

Ask Directly About Oil Top-Ups

Do not just ask whether the car burns oil. Ask how much oil has been added between services and how often. A clear answer is useful; “they all do that” is not.

Check the Oil Level Correctly

Check it on level ground and follow the correct procedure for the vehicle. A low level can indicate consumption or leakage. An oil level above maximum can indicate diesel dilution from repeated or interrupted DPF regenerations.

If the oil level is rising rather than falling, do not assume the engine has somehow made oil. Diesel may be entering the sump during unsuccessful regeneration attempts, thinning the engine oil and reducing its ability to protect the engine.

Start the Engine From Cold

A warm engine can hide smoke, difficult starting and unusual noises. Ask the seller not to start the car before you arrive. Watch the exhaust on start-up and again after the engine has idled.

Check the Servicing Properly

Look for invoices, dates and recorded mileages rather than relying on the words “full service history” in the advert. Confirm that the correct low-ash oil approval has been used for the engine. On many of these cars that will be VW 507 00, but it should still be confirmed against the vehicle's handbook or VIN.

Carry Out a Full Diagnostic Scan

The scan should go further than checking for a current warning light. Useful DPF information includes:

• Calculated and measured soot loading
• Ash loading
• Differential pressure at idle and under load
• Distance or time since the last regeneration
• Aborted or unsuccessful regenerations
• Exhaust-temperature sensor readings
• Engine coolant temperature
• EGR and injector-related fault codes

A forced regeneration is not a repair if another fault is causing the DPF to load up.

Complete a Proper Road Test

The engine should reach normal operating temperature and pull cleanly without hesitation, smoke or limp mode. Check whether the cooling fans run excessively and whether any warning messages appear after the car is worked properly.

Check the Rest of the Drivetrain

If it has a DSG gearbox, look for evidence that it has been serviced at the correct intervals for the gearbox fitted. Check for hesitation, shuddering and harsh engagement when cold. On a manual, check the clutch and dual-mass flywheel for slip, vibration, judder or rattling.

Timing-belt and water-pump history should also be confirmed rather than assumed.

Questions to Ask the Seller

• How much oil does it use between services?
• When was the oil last topped up?
• Has the DPF warning light ever come on?
• Has it ever needed a forced regeneration or DPF clean?
• What type of journeys has the car mainly completed?
• Have the EGR valve, DPF sensors, turbocharger or injectors ever been replaced?
• Is there diagnostic evidence showing the current DPF soot and ash levels?
• Has the correct engine oil been used?
• When were the timing belt and water pump last replaced?
• If it is DSG, when was the gearbox last serviced?

Technician's Inside Tip

Oil consumption and DPF trouble can also feed into each other. Oil burned by the engine creates ash that a regeneration cannot remove. The DPF's usable capacity falls, regeneration frequency increases and more interrupted regenerations can then contaminate the engine oil with diesel.

This is why simply forcing a regeneration or clearing the warning light is not enough. The reason the DPF is loading up needs finding first.

Alfie Hill

Founder & Lead Advisor

Alfie has over 11 years of experience in the motor trade and founded Alfa Prestige to give buyers the insider knowledge that was previously only available to professionals.