CZDA engine increasing fuel consumption at higher speeds

[Balazs_HU]

Dear Forum members,

 

I have a peculiar problem with my 2015 Skoda Octavia Combi (CZDA 1.4 TSI engine, 150 hp). When I use it for my daily commute (about 20 km both ways) it returns a nice 5,5 liters/100 kilometers (around 44 mpg) on country roads, but when I go on the motorway, it's appalling to be honest. I remember when I bought it setting the cruise control to either 140 or 150 km/h and it returned around 6,2-6,4 liters/100 kilometers (36-37 mpg), but in recent memory that would go as low/high (depending if mpg or liters/100 kilometers) as 8,8-5 liters/100 kilometers (27-29mpg) and I have no idea why. It was in my experience a gradual process so I can't really tie it to any of the services done on the car. It has done 210k kilometers, the cambelt was changed 2 years ago, oil change services done in 10k intervals, there are no fault codes to read, and if I notice something unusual I go to get the car serviced, so I have no idea. Also the inlet valves were cleaned with walnut a year ago so it should be okay. Is there any more common issues I can try to ask my mechanic to check if it is the cause of the high fuel consumption?

 

Edit: all 4 glow plugs have been replaced in due time and I only fill the car with 100 octane petrol.

 

Thanks in advance!

 

Cheers,

 

Balázs

Edited 19 April by Balazs_HU

[ords]

28 minutes ago, Balazs_HU said:

Dear Forum members,

 

I have a peculiar problem with my 2015 Skoda Octavia Combi (CZDA 1.4 TSI engine, 150 hp). When I use it for my daily commute (about 20 km both ways) it returns a nice 5,5 liters/100 kilometers (around 44 mpg) on country roads, but when I go on the motorway, it's appalling to be honest. I remember when I bought it setting the cruise control to either 140 or 150 km/h and it returned around 6,2-6,4 liters/100 kilometers (36-37 mpg), but in recent memory that would go as low/high (depending if mpg or liters/100 kilometers) as 8,8-5 liters/100 kilometers (27-29mpg) and I have no idea why. It was in my experience a gradual process so I can't really tie it to any of the services done on the car. It has done 210k kilometers, the cambelt was changed 2 years ago, oil change services done in 10k intervals, there are no fault codes to read, and if I notice something unusual I go to get the car serviced, so I have no idea. Also the inlet valves were cleaned with walnut a year ago so it should be okay. Is there any more common issues I can try to ask my mechanic to check if it is the cause of the high fuel consumption?

 

Edit: all 4 glow plugs have been replaced in due time and I only fill the car with 100 octane petrol.

 

Thanks in advance!

 

Cheers,

 

Balázs

You mean spark plugs?

[Balazs_HU]

56 minutes ago, ords said:

You mean spark plugs?

Absolutely!

[Ootohere]

Do you really need to be changing the oil @ 10,000 km,  as 15,000 km / 9,400 miles would be fine with or annually without long life oil.

 

Is it VW502 00  5w 40 FS you use or VW 504 00 / 507 00, 5w 30 FS III ?

 

Is it E5 95 ron petrol you use, 

& is there a nice clean air filter fitted? 

[Gerrycan]

@Balazs_HU, fuel consumption variations are generally difficult to account for.

 

A minor point but I think you may have used the smaller USA gallons instead of the larger Imperial (British) gallon for your conversions so 5.5L/100 is 51 mpg, 6.2 - 6.4L/100 is 45 to 44 mpg and 8.0 - 8.5L/100 is 35 to 37 mpg.

 

I have a 2014 1.4tsi combi that has only done 105,000 km and there is no doubt in my mind that the engine is a really good, economical unit....however like most petrol engines it drinks noticeably more if you use the performance or if there are adverse road or environmental factors.

 

Based on some official VW issued consumption figures I have seen for early 1.4tsi engines and my own experience I find it hard to believe that your car would have consistently achieved your claimed displayed consumption of 6.2 to 6.4l/100 at real 140 to 150 kph speeds. A diesel could possibly do it or maybe even a mk4 1.5tsi with it's better aerodynamics and longer gearing but that is a moot point.

 

Most British drivers on their roads would not have the freedom to travel at those speeds for any distance without incurring punitive fines and the same here in most of Australia where I live. 

Quite honestly travelling at a true 130kph in good conditions and I am really happy to get 7L/100, which corresponds with VW claims. Obviously consumption increases with speed.

 

A headwind or stiff crosswind can adversely affect consumption by 1.0 to 1.5L/100 at 110kph in my experience. Equally a tailwind or travelling at speed in enforced reasonably close proximity to other traffic can benefit consumption by similar amounts.

 

If your car has a real consumption problem that is only manifesting itself at higher speeds then it probably has to do with the higher airflows.

As @Rooted says check your air-filter is clean as a first step but it gets more difficult from there.

Other possibilities may be turbo related or maybe the variable valve timing is not performing as it should? I imagine the only way to disprove either is to put the car on a dynamometer and see if peak outputs are below par?

 

Personally I think your current consumptions at both low and high speeds are quite realistic.

Edited 20 April by Gerrycan

[Balazs_HU]

On 19/04/2024 at 20:02, Rooted said:

Do you really need to be changing the oil @ 10,000 km,  as 15,000 km / 9,400 miles would be fine with or annually without long life oil.

 

Is it VW502 00  5w 40 FS you use or VW 504 00 / 507 00, 5w 30 FS III ?

 

Is it E5 95 ron petrol you use, 

& is there a nice clean air filter fitted? 

I use 100 octane petrol and 5W30 oil. The air filter is replaced with every oil change at around every 10-13000 kilometers. I like to  be sure with my oil changes to be honest. I understand that this might be too often but I'd like to be on the safe side (had a few lemons before that really loved oil so maybe that's why I'd like to take care of my car as best as possible).

On 20/04/2024 at 03:00, Gerrycan said:

@Balazs_HU, fuel consumption variations are generally difficult to account for.

 

A minor point but I think you may have used the smaller USA gallons instead of the larger Imperial (British) gallon for your conversions so 5.5L/100 is 51 mpg, 6.2 - 6.4L/100 is 45 to 44 mpg and 8.0 - 8.5L/100 is 35 to 37 mpg.

 

I have a 2014 1.4tsi combi that has only done 105,000 km and there is no doubt in my mind that the engine is a really good, economical unit....however like most petrol engines it drinks noticeably more if you use the performance or if there are adverse road or environmental factors.

 

Based on some official VW issued consumption figures I have seen for early 1.4tsi engines and my own experience I find it hard to believe that your car would have consistently achieved your claimed displayed consumption of 6.2 to 6.4l/100 at real 140 to 150 kph speeds. A diesel could possibly do it or maybe even a mk4 1.5tsi with it's better aerodynamics and longer gearing but that is a moot point.

 

Most British drivers on their roads would not have the freedom to travel at those speeds for any distance without incurring punitive fines and the same here in most of Australia where I live. 

Quite honestly travelling at a true 130kph in good conditions and I am really happy to get 7L/100, which corresponds with VW claims. Obviously consumption increases with speed.

 

A headwind or stiff crosswind can adversely affect consumption by 1.0 to 1.5L/100 at 110kph in my experience. Equally a tailwind or travelling at speed in enforced reasonably close proximity to other traffic can benefit consumption by similar amounts.

 

If your car has a real consumption problem that is only manifesting itself at higher speeds then it probably has to do with the higher airflows.

As @Rooted says check your air-filter is clean as a first step but it gets more difficult from there.

Other possibilities may be turbo related or maybe the variable valve timing is not performing as it should? I imagine the only way to disprove either is to put the car on a dynamometer and see if peak outputs are below par?

 

Personally I think your current consumptions at both low and high speeds are quite realistic.

Thanks for the feedback! I did not know the difference between the gallons, I've used the converter on google.

 

I understand that your evaluation might be the correct one but for some reason I remember the car having better fuel economy a year or two ago. Or maybe I am just overreacting because the ****ty cars we had before the Octy just broke down (An old Citroen C5 with the 2.0 HDi lost compression and a Fiat Stilo with the infamous 1.8 petrol excessively consuming oil after an enginge rebuild only to stop this habit when we sold it) after us using them for 70,000 kilometers and I am getting nervous out of habit

 

Indeed I like the engine a lot,  it can be quite economical while having more than enough power for me at least.

 

Nevertheless, I am still curious if there are some more common issues leading to higher fuel consumption at higher speeds just to be sure I can check them and be happy with the car.

 

[Ootohere]

My step daughters husband in Hungary runs a 2.0 TDI Mk3 Octavia Estate and has had nothing but bother with it.

They just got a newer 2nd car and he is now using it rather than the Octavia. A Renault Capture. 

[Balazs_HU]

1 minute ago, Rooted said:

My step daughters husband in Hungary runs a 2.0 TDI Mk3 Octavia Estate and has had nothing but bother with it.

They just got a newer 2nd car and he is now using it rather than the Octavia. A Renault Capture. 

There always will be lemons. The main reason we bought a Skoda was the lack of posts related to issues with the car in Facebook groups. I only had a few issues (the famous TSi fuel rail screw thing got me), but nothing major. Compared to what we were used to the car is really reliable. I don't know much about diesels, but with proper maintenance they are said to be reliable too.

 

But for reference, the 2.0 HDi is also said to be very reliable, yet we had all kinds of issues with ours. Suprisingly, the electronics worked will in that Citroen, as they worked well in the Fiat as well. 

 

I think to you need luck to some degree when buying a car, because you are not going to be able to foresee all mechanical failures.  

[Gerrycan]

@Balazs_HU, other than the expense there is obviously no harm in servicing earlier than required, may even be necessary if doing track work, but it doesn't necessarily guarantee greater reliability either.

Changing the intake air filter as regularly as you do also seems a bit of an overkill but are you sure they are actually replacing it? 

 

The only other thing I can suggest checking is the accuracy of the displayed consumption. The only way really is to look at the 'since refuel' consumption display and compare it with the calculated consumption when you refuel the car. Try to use the same refuel procedure each time.

 

When my car was brand new the displayed consumption was actually worse than I was really achieving by about 0.2L/100, then by about 40,000 km it changed to being absolutely accurate then by 80, 000 km the display had changed to being about 0.2L better than I was actually getting. Now it has swung back to being truer again. These are small variations for me but maybe yours are greater?

 

Other things to look for that may affect high speed consumption are:

Whether the undertray is still in place (significantly worse aerodynamics at speed), after all the thing would have been taken off a number of times with the number of services the vehicle has had, maybe it got damaged and not replaced by the mechanic?

Whether the consumption change is related to a tyre size change (unlikely to affect it by that much though). I presume if you are travelling at those speeds they are at an appropriate pressure and checked regularly.

 

I'm clearly running out of ideas now

 

Edited 22 April by Gerrycan

[varaderoguy]

My thoughts are that maybe you have a sticking caliper that is potentially causing issues. Octavia and Golfs are notorious for binding brakes.

[Gerrycan]

21 hours ago, varaderoguy said:

My thoughts are that maybe you have a sticking caliper that is potentially causing issues. Octavia and Golfs are notorious for binding brakes.

Should be checked for sure but I would have thought the affects would be across the speed spectrum and his lower speed consumption is still pretty good.

At 150kph sticking brakes would glow in the dark  

[Balazs_HU]

22 hours ago, Gerrycan said:

@Balazs_HU, other than the expense there is obviously no harm in servicing earlier than required, may even be necessary if doing track work, but it doesn't necessarily guarantee greater reliability either.

Changing the intake air filter as regularly as you do also seems a bit of an overkill but are you sure they are actually replacing it? 

 

The only other thing I can suggest checking is the accuracy of the displayed consumption. The only way really is to look at the 'since refuel' consumption display and compare it with the calculated consumption when you refuel the car. Try to use the same refuel procedure each time.

 

When my car was brand new the displayed consumption was actually worse than I was really achieving by about 0.2L/100, then by about 40,000 km it changed to being absolutely accurate then by 80, 000 km the display had changed to being about 0.2L better than I was actually getting. Now it has swung back to being truer again. These are small variations for me but maybe yours are greater?

 

Other things to look for that may affect high speed consumption are:

Whether the undertray is still in place (significantly worse aerodynamics at speed), after all the thing would have been taken off a number of times with the number of services the vehicle has had, maybe it got damaged and not replaced by the mechanic?

Whether the consumption change is related to a tyre size change (unlikely to affect it by that much though). I presume if you are travelling at those speeds they are at an appropriate pressure and checked regularly.

 

I'm clearly running out of ideas now

 

I am quite sure they replace everything because they leave the stuff they replace so I can check it. Accuracy is 0,2L/100 better on the computer than in real life, I tried that. I haven't checked the undertray, but it seems in place to be honest. Also I was suspecting tyre pressure first for higher consumption, but not, that was also good. 

 

Me too, I also run out of ideas. I suspect the problem is either technical of psychological in nature

21 hours ago, varaderoguy said:

My thoughts are that maybe you have a sticking caliper that is potentially causing issues. Octavia and Golfs are notorious for binding brakes.

I checked that too, the rims are not at all warm after a longer trip, or not warmer than everything else. Good point though!

Just now, Gerrycan said:

Should be checked for sure but I would have thought the affects would be across the speed spectrum and his lower speed consumption is still pretty good.

At 150kph sticking brakes would glow in the dark  

Yeah, that is strange part, lower speed consumption is quite okay. Last tank was only country road driving, on average it was 5,3L/100km real consumption.

[Gerrycan]

I have found the VW consumption information I referenced in an earlier post on a backup of my old computer.

As I said it is for the old 90kw 1.4tsi manual in a Golf but the reference points upto 130kph are almost identical on my 103kw manual version so I would not expect too much difference with your 110kw output version.

 

It confirms my theory that your original consumption displays at speed were quite unusually good.

 

 

 

Edited 23 April by Gerrycan