Hello, good folks of briskoda. I need some help figuring out why my mk3 2015 Octavia TDI is giving me low fuel efficiency. I'm getting anywhere between 5-9 kmpl (11-21 mpg) in city driving and around 17-19 kmpl (39-45) on highways. The latter seems decent but the city numbers seem way below what my friends with Octavias and Jettas are getting.
In the city, I can almost feel a sluggish pull when I'm in lower gears. And when I've taken my foot off the accelerator, the engine braking seems too eager to slow the car down.
For background, the car has run 160k km (100k miles). I bought it around 5 months back secondhand. Changed the flywheel, engine mounts, wheel dents were removed, aligned and balanced, full service was done with engine oil,fuel filter, oil filter and air filter changes, gear box oil was inspected and topped up.
The previous owner mentioned that he had changed the timing belt and water pump roughly 70k km (50k mile) ago.

I met up with a friend last weekend and he ran a bit of vcds diagnostics. Turbo performance seems to be good. One thing that stood out was that the fuel pressure was lagging behind the ECU specified value. PFA graph.

When he cleared the short term fuel trims, on my drive back in the city, I was getting 12.5 Kmpl (29mpg). This was much higher than the usual and the car seemed eager to start moving in the lower gears as soon as my foot was off the brake. Not sure if this was just placebo. I didn't get a chance to check again since I was away for work for a week or so. Got back this week, driving around, back to square 1. 5-8 Kmpl in city (albeit start stop traffic) I got 17.5 on late night drive to airport, which compared to other people's cars on long drives, seems lower.

Occasionally, while driving, I get the error "only leave vehicle in position P, please visit workshop" but it comes on for a second and goes away. Not sure if this is doing anything.

Also, the timing belt stretch was measured at 3.98°.

Any ideas on where I should start looking for solves?

 

Considering doing a complete change of DSG oil, fuel pump change, timing belt and water pump but that's a big spend. 

Edited 8 October, 20241 yr by Octaviaboy

What's the engine size?

Hello, welcome to the forum. Have you checked for binding brakes?

2L TDI. 140 bhp, 320 Nm variant. 

14 hours ago, ords said:

What's the engine size?

2L TDI. 140 bhp, 320 Nm variant. 

13 hours ago, Warrior193 said:

Hello, welcome to the forum. Have you checked for binding brakes?

I haven't. But I had the pads changed when I bought it around 5 months back. 

20 hours ago, Octaviaboy said:

Changed the flywheel, engine mounts, wheel dents

Why, why. and what does "wheel dents" mean in English?

 

Personally I'd not expect "normal economy" from a diesel until it had done about 15 minutes or 15km driving from cold.

3 hours ago, Octaviaboy said:

I haven't. But I had the pads changed when I bought it around 5 months back. 

I suggest checking all wheel hubs for unusual heating after driving a few kilometres - preferably somewhere where hard braking is not required.

Is it doing many regens? Could be a DPF problem.

11 hours ago, Paws4Thot said:

Why, why. and what does "wheel dents" mean in English?

 

Personally I'd not expect "normal economy" from a diesel until it had done about 15 minutes or 15km driving from cold.

Flywheel was making a ticking noise. 

Engine mount was changed because I could feel the vibrations on the steering. 

Haha by wheel dents, I meant bent wheel from presumably jumping into potholes. I was feeling vibrations after 100 Kmph. Took it to wheel balancing, they mentioned that the alloy had bents from impact. Got that fixed. 

 

You make a good point about the distance/time. Thing is, my first 15 minutes is usually stuck in traffic traveling maybe 3 Km. I'll try an early morning run without traffic and see where I land. 

8 hours ago, Warrior193 said:

I suggest checking all wheel hubs for unusual heating after driving a few kilometres - preferably somewhere where hard braking is not required.

Oh, I'll do that. Will try an early morning run. I do feel during higher speeds, there's some running noise. Not sure if it's the tyres or bearings.

 

Also, the thing is, the sluggish feeling exists in gears 1-2, maybe 3. Like the instantaneous kmpl shows as low as 2.8-3.1 Kmpl (6.5-7.2 mpg) even when slow accelerating in gear 2. Once it's in 4, it feels super smooth, like the car doesn't engine break if my foot is off the accelerator. I'm wondering if it's a gear thing. The transmission fluid temperature showed 95°C after around half an hour of driving. 

What gearbox mode have you selected?

4 hours ago, ords said:

Is it doing many regens? Could be a DPF problem.

Do you know what I should be checking for on the VCDS for this? I do have a lot of short city drives usually. Long drives are a rarity.

3 minutes ago, ords said:

What gearbox mode have you selected?

Always in D, rarely in S. It's the 2015 Mk3 TDI so there's no Eco mode or such.

1 hour ago, Octaviaboy said:

Oh, I'll do that. Will try an early morning run. I do feel during higher speeds, there's some running noise. Not sure if it's the tyres or bearings.

 

Also, the thing is, the sluggish feeling exists in gears 1-2, maybe 3. Like the instantaneous kmpl shows as low as 2.8-3.1 Kmpl (6.5-7.2 mpg) even when slow accelerating in gear 2. Once it's in 4, it feels super smooth, like the car doesn't engine break if my foot is off the accelerator. I'm wondering if it's a gear thing. The transmission fluid temperature showed 95°C after around half an hour of driving. 

I'd suggest ignoring instantaneous fuel readings, try using the average ones for a more meaningful calculation.  

1 hour ago, Octaviaboy said:

 I do have a lot of short city drives usually. Long drives are a rarity.

 

 

This is a big contribution I think.

Also, a gearbox top up on DSG is not usual. There is a process to follow involving vcds to empty and refill the galleries. What determined the need top top it up.

49 minutes ago, Warrior193 said:

I'd suggest ignoring instantaneous fuel readings, try using the average ones for a more meaningful calculation.  

The average comes out to around 7 Kmpl for like a 10 Km ride. In the city with a lot of traffic lights. I'm concerned because my friends are getting twice that almost in similar conditions. 

18 minutes ago, MarkyG82 said:

 

This is a big contribution I think.

So I try to do a static dpf regen some time and check after that?

16 minutes ago, MarkyG82 said:

Also, a gearbox top up on DSG is not usual. There is a process to follow involving vcds to empty and refill the galleries. What determined the need top top it up.

The mechanic had checked it when the car was with him for the engine mount replacement. He had initially said he'd change the oil but later said that when he inspected it, found that a top up would suffice. 0.5L topped up, iirc. 

2 hours ago, Octaviaboy said:

Do you know what I should be checking for on the VCDS for this? I do have a lot of short city drives usually. Long drives are a rarity.

Always in D, rarely in S. It's the 2015 Mk3 TDI so there's no Eco mode or such.

Mine has Eco

Looks not ok. My '2016 2.0TDI 110kw is getting 47...35 UK mpg (6...8 L/100km) in the city. Disabled start-stop, manual gearbox, 225mm wide tyres, Auto Clima always on. On higway drive is steady 64 mpg (4.4 L/100km)

How sure are you of the high quality of the fuel in the car?