MPG a bit low?

[snowathlete]

Filled up the car just before we went on the motorway today, spent about 40 minutes on the motorway having reset the average MPG computer. I understand the reading is generally optimistic and yet we only got about 45 MPG on the motorway driving at 70, most of it with cruise control on. Yes, it's DSG and 4x4 but 4 new tyres with proper alignment done, good rolling resistance, all the oils and filters new etc. From what I read on here we should be getting better than that?

 

Related to this, most of our normal driving is short distance, trips to school, 20 minute drives, etc. non-motorway, so we expect poorer MPG on those trips, but we only got 28 miles to the gallon on our first full tank, brim to brim, which even with those shorter journeys seemed low.

 

Do I have too high expectations or is the car coming up a bit short?

[pinkpanther]

I guess it might depend on the status of the DPF, given the short distances driven previously.

 

My (6 speed manual) 4x4 Yeti has the 140 BHP version of your engine and only manages mid 40's MPG. I guess the Superb might be a little more aerodynamic (??).

 

A family member previously ran a 177 BHP Audi A6 (similar size to your Superb) in mainly urban commuting and this averaged mid 20' s MPG, although returned 50's MPG on long motorway cruises.

 

I guess the other question is has your car had the EA189 update, as this is known to both increase the frequency of DPF regeneration and reduce fuel economy.

 

More here: 

https://www.honestjohn.co.uk/realmpg/skoda/superb-2008

 

and here: http://www.fuelly.com/car/skoda/superb/2014

Edited 5 February, 2018 by pinkpanther

[snowathlete]

Yes, previous owner had the "fix". Otherwise DPF is ok. But we intend to get it rolled back. Shark Performance too far away from us but found a couple of options closer who seem to know what they are talking about. Need to inquire about price and maybe see if there are any other places locally, but we'll be getting it done. It'll be interesting to see if it is a factor but thought it would be good to gauge opinion on whether my car is under performing or not and whether there might be something else wrong and what we can check.

 

Official combined figure for my model is I think 50mpg. Honest John Real MPG says it is 45.6 with real MPG being higher. I think it's higher because the official figure is wrong. Either way, we don't seem to be achieving anything close to that.  I know we won't achieve these top figures most of the time with the types of journeys we do, but the figures we're getting seem low.

 

[jafo]

I think it's pretty normal mpg for stock car. Fix is not helping either. 

 

You need to un-fix it asap and then re-map / chip it.

Edited 5 February, 2018 by jafo

[pinkpanther]

6 hours ago, snowathlete said:

Yes, previous owner had the "fix". Otherwise DPF is ok. But we intend to get it rolled back. Shark Performance too far away from us but found a couple of options closer who seem to know what they are talking about. Need to inquire about price and maybe see if there are any other places locally, but we'll be getting it done. It'll be interesting to see if it is a factor but thought it would be good to gauge opinion on whether my car is under performing or not and whether there might be something else wrong and what we can check.

 

Official combined figure for my model is I think 50mpg. Honest John Real MPG says it is 45.6 with real MPG being higher. I think it's higher because the official figure is wrong. Either way, we don't seem to be achieving anything close to that.  I know we won't achieve these top figures most of the time with the types of journeys we do, but the figures we're getting seem low.

 

My MPG fell around 12% post EA189 update. Following a stage 1 remap it recovered to pre-update levels. More here: https://www.briskoda.net/forums/topic/429970-ea189-emmisions-update-my-experience/

 

My aim with the remap was to reduce load on DPF / EGR etc, rather than simply improve MPG.

 

All things being considered (and assuming no physical faults with your car) I'd say your MPG is within the expected range, given it's both 4x4 and DSG.

 

Good luck with a resolution

 

 

[HughGabriel]

@snowathlete I managed the first brim-brim fill at the weekend too, 36mpg calculating it, 42mpg on the dash.  Our is 2wd 140.   For reference our previous 170 2wd Passat averaged mid-40s calculating it.

[PipH]

If you had reset the computer just before the motorway journey when the engine was already up to temperature, I think your MPG is a bit low.

I have a 2l 140 Passat Estate & would expect to see over 60mpg at 70.

Mine is not 4x4 so that will obviously take its toll. ( perhaps 10% )

The DSG should give better MPG on the motorway, higher top gear than manual box I belive.

 

Most common cause of poor consumption is the coolant thermostat either opening too early or stuck partially open.

If you've got a few spare minutes on a journey from cold, stop the car when the temp guage is starting to move up from 50c.

Choose a safe place & pop the bonnet, feel the top of the radiator.

It should be stone cold.

If it's warm then water is circulating when it shouldn't & loosing you MPG.

The DSG engine has 2 thermostats, one for the engine & one for the DSG.

It seems the DSG stat is a fairly common failure.

[snowathlete]

Yes the engine was up to temp by then PipH. Overall I'd expect a loss of maybe up to 3-10% because of the 4x4, probably the lower end because a lot of the time it is not engaged much,I think on the motorway in particular it should be virtually disengaged the whole time. At any rate it seems to be much lower than it should be given most people's experience.

 

Really helpful tips for diagnosing what might be happening, thank you. I will try it. Will you get the same symptom at the radiator if the DSG stat fails, or just the main stat? 

[HughGabriel]

1 hour ago, PipH said:

DSG should give better MPG on the motorway, higher top gear than manual box I belive

 

I’m not sure about this, at 70mph our Superb is doing 2200rpm.  Our previous Passat (manual 170), and current Golf (manual 140) are both doing ~1750rpm at 70mph.  I’d have thought the lower revs would give better fuel economy.

 

Unless you are suggesting the Manual Superb is even lower geared and would be doing more than 2200rpm at 70???

 

Editted to say both Passat & Golf are Bluemotion Tech models.

Edited 5 February, 2018 by HughGabriel
Clarification

[cssuk]

just bought a 170  6 spd dsg but 2wd superb which has not had the fix on the way home from southampton at 80-85 on the mway it gave 44mpg previous passat 140 would do 47 at similar speeds so am happy with that.

[bigjohn]

18 hours ago, snowathlete said:

Yes, previous owner had the "fix". Otherwise DPF is ok. But we intend to get it rolled back. Shark Performance too far away from us but found a couple of options closer who seem to know what they are talking about. Need to inquire about price and maybe see if there are any other places locally, but we'll be getting it done. It'll be interesting to see if it is a factor but thought it would be good to gauge opinion on whether my car is under performing or not and whether there might be something else wrong and what we can check.

 

Official combined figure for my model is I think 50mpg. Honest John Real MPG says it is 45.6 with real MPG being higher. I think it's higher because the official figure is wrong. Either way, we don't seem to be achieving anything close to that.  I know we won't achieve these top figures most of the time with the types of journeys we do, but the figures we're getting seem low.

 

 

The official figures improved on the facelift model which I think yours is, which may explain the lower figure on HJ

 

There are many reports of worse fuel consumption after the dieselgate fix - so hopefully it will improve after you roll back the fix. I can't comment myself as mine drinks from the other pump!

 

PS keep an eye on the oil level - if the DPF regens are failing for whatever reason it may be "using" diesel on regens which can drop past the pistons/bores and dilute the sump oil with diesel

Edited 5 February, 2018 by bigjohn

[PipH]

4 hours ago, snowathlete said:

Yes the engine was up to temp by then PipH. Overall I'd expect a loss of maybe up to 3-10% because of the 4x4, probably the lower end because a lot of the time it is not engaged much,I think on the motorway in particular it should be virtually disengaged the whole time. At any rate it seems to be much lower than it should be given most people's experience.

 

Really helpful tips for diagnosing what might be happening, thank you. I will try it. Will you get the same symptom at the radiator if the DSG stat fails, or just the main stat? 

I didn't realise the 4x4 was part time.

So as you say, won't have as much impact on MPG.

I might be wrong re the gearing, I think my engine revs at about 2100 @ 70 on the spedo which equates to 70 on cruise, probably a true 67.

 

I havn't seen a cooling system diagram for a Superb, but heat from the DSG has to be dissipated so must go through the rad.

[TheRobinK]

4 hours ago, HughGabriel said:

I’m not sure about this, at 70mph our Superb is doing 2200rpm.

 

Doesn't sound quite right to me either - at 75mph, my 1.6 D manual would be doing  2000rpm in 6th. That's 75 on the cars speedo - if doing a true 75 measured with a satnav, its about 2100 rpm.

 

[bigjohn]

25 minutes ago, TheRobinK said:

 

Doesn't sound quite right to me either - at 75mph, my 1.6 D manual would be doing  2000rpm in 6th. That's 75 on the cars speedo - if doing a true 75 measured with a satnav, its about 2100 rpm.

 

 

Unless it's to do with the revised 6 speed manual gearbox on the facelift 1.6- pre facelift was a 5 speed box

 

 

[snowathlete]

2 hours ago, PipH said:

I didn't realise the 4x4 was part time.

So as you say, won't have as much impact on MPG.

I might be wrong re the gearing, I think my engine revs at about 2100 @ 70 on the spedo which equates to 70 on cruise, probably a true 67.

 

I havn't seen a cooling system diagram for a Superb, but heat from the DSG has to be dissipated so must go through the rad.

 

My revs are the same at that speed. I don't know for sure the configuration is the same on the Golf CFGB engine as on the Superb CFGB but here is the diagram on the Golf. I don't fully understand the system, particularly with the DSG stat in there as well but would like to.

http://workshop-manuals.com/volkswagen/golf-mk5/heating_ventilation_air_conditioning_system/auxiliary_heater/aux._heater/heater_booster/connecting_auxiliary_heater_thermo_top_v_to_coolant_circuit/connection_diagram_for_coolant_hoses_in_vehicles_with_auxiliary_heating_engine_codes_cffa_cffb_cfgb/

 

[HughGabriel]

8 hours ago, TheRobinK said:

 

Doesn't sound quite right to me either - at 75mph, my 1.6 D manual would be doing  2000rpm in 6th. That's 75 on the cars speedo - if doing a true 75 measured with a satnav, its about 2100 rpm.

 

 

Got a long drive Saturday and Sunday so I’ll double check, but I’m fairly certain that’s what I remember from because I was surprised it was so high when we first got the car.  

[PipH]

11 hours ago, snowathlete said:

 

My revs are the same at that speed. I don't know for sure the configuration is the same on the Golf CFGB engine as on the Superb CFGB but here is the diagram on the Golf. I don't fully understand the system, particularly with the DSG stat in there as well but would like to.

http://workshop-manuals.com/volkswagen/golf-mk5/heating_ventilation_air_conditioning_system/auxiliary_heater/aux._heater/heater_booster/connecting_auxiliary_heater_thermo_top_v_to_coolant_circuit/connection_diagram_for_coolant_hoses_in_vehicles_with_auxiliary_heating_engine_codes_cffa_cffb_cfgb/

 

Thanks for the link to the diagram snowathlete, although it's not the correct car it's probably typical for this engine.

 

It doesn't show a DSG stat, but that must be in the pipe between 6 & 7.

 

So as I understand it, & I stand to be corrected by anyone who knows better, but the coolant flow would be as follows :-

 

The pump 2 circulates coolant around the block/cylinder head 3, heated coolant exits from the horizontal pipe at the right end of the block.

Assuming the engine is cold, coolant won't be able to pass the thermostat 10.

 

The first vertical pipe going down from the group of 4 at the right end of the block must be a small bore pipe going back to the thermostat located in 10. I assume this is to sense the coolant temp coming from the head so that the thermostat opens at the preset temperature of the stat.

 

The main coolant flow with the stat closed will be the extreem right pipe of the 4 coming from the head, this will go straight to the heater matrix 5, as most cars won't have 11 & 12 installed.

It looses its heat from the matrix & returns to the bottom of the engine via 10.

It circulates like that until the engine gets up to temperature when the thermostat in 10 opens.

 

When the stat opens coolant is alowed to circulate down the second vertical pipe of the 4, this will be a large bore pipe going to the top of the rad, through the radiator 9 & back to the bottom of the engine via 10.

Coolant is also still flowing through the heater matrix which is effectively in parallel with the main rad.

 

There is also another parallel coolant flow connected to that large bore pipe, this goes via the EGR cooler 4 & electric pump 8.

I think this pump only runs at certain times, certainly not during a regen, but that is just a guess.

 

The stat in 10 regulates the main flow depending on the temperature of the coolant being sensed.

 

If the DSG stat was open, coolant flows via that single central pipe at the bottom of the block, via 6, DSG stat & 7, back to the bottom of the engine, so short circuits the whole system.

So I was wrong in that it doesn't go directly via the rad as per my previous post, so it wont be easy to detect that it has failed open.

 

Checking the rad as I suggested will only be checking the main thermostat which rarely seem to go wrong.

 

If you look half way down this post there is a picture of the DSG stat & its location under the air filter.

https://www.pistonheads.com/gassing/topic.asp?h=0&f=66&t=1610899

 

You would have to expose these pipes then start the engine from cold.

These pipes should remain cold while the engine warms up, but a bit of a faf to check.

 

 

[lichfielddriver]

blimey, now im worried

 

my 1.6 Superb did 64mpg on a run, 50mpg round town and 54mpg overall

 

my E250 estate does 45mpg overall

 

seriously looking at a 2ltr Superb but not DSG or 4wd, is the octavia more economical?

[TasMan]

On ‎05‎/‎02‎/‎2018 at 17:28, HughGabriel said:

 

I’m not sure about this, at 70mph our Superb is doing 2200rpm.  Our previous Passat (manual 170), and current Golf (manual 140) are both doing ~1750rpm at 70mph.  I’d have thought the lower revs would give better fuel economy.

 

Unless you are suggesting the Manual Superb is even lower geared and would be doing more than 2200rpm at 70???

 

Checked mine this morning, 6 speed manual 4x4......In 6th gear at 60 MPH its sitting at 1700 RPM, at 70 MPH its 2000 RPM.

I am sure I read somewhere the manual 4x4 is slightly lower geared, not sure if that helps at all ?

Cheers

[snowathlete]

On 06/02/2018 at 12:35, PipH said:

Thanks for the link to the diagram snowathlete, although it's not the correct car it's probably typical for this engine.

 

It doesn't show a DSG stat, but that must be in the pipe between 6 & 7.

 

So as I understand it, & I stand to be corrected by anyone who knows better, but the coolant flow would be as follows :-

 

The pump 2 circulates coolant around the block/cylinder head 3, heated coolant exits from the horizontal pipe at the right end of the block.

Assuming the engine is cold, coolant won't be able to pass the thermostat 10.

 

The first vertical pipe going down from the group of 4 at the right end of the block must be a small bore pipe going back to the thermostat located in 10. I assume this is to sense the coolant temp coming from the head so that the thermostat opens at the preset temperature of the stat.

 

The main coolant flow with the stat closed will be the extreem right pipe of the 4 coming from the head, this will go straight to the heater matrix 5, as most cars won't have 11 & 12 installed.

It looses its heat from the matrix & returns to the bottom of the engine via 10.

It circulates like that until the engine gets up to temperature when the thermostat in 10 opens.

 

When the stat opens coolant is alowed to circulate down the second vertical pipe of the 4, this will be a large bore pipe going to the top of the rad, through the radiator 9 & back to the bottom of the engine via 10.

Coolant is also still flowing through the heater matrix which is effectively in parallel with the main rad.

 

There is also another parallel coolant flow connected to that large bore pipe, this goes via the EGR cooler 4 & electric pump 8.

I think this pump only runs at certain times, certainly not during a regen, but that is just a guess.

 

The stat in 10 regulates the main flow depending on the temperature of the coolant being sensed.

 

If the DSG stat was open, coolant flows via that single central pipe at the bottom of the block, via 6, DSG stat & 7, back to the bottom of the engine, so short circuits the whole system.

So I was wrong in that it doesn't go directly via the rad as per my previous post, so it wont be easy to detect that it has failed open.

 

Checking the rad as I suggested will only be checking the main thermostat which rarely seem to go wrong.

 

If you look half way down this post there is a picture of the DSG stat & its location under the air filter.

https://www.pistonheads.com/gassing/topic.asp?h=0&f=66&t=1610899

 

You would have to expose these pipes then start the engine from cold.

These pipes should remain cold while the engine warms up, but a bit of a faf to check.

 

 

 

Thanks for taking the time to explain that, it makes sense now that you've pointed it all out to me. So the DSG has it's own stat so that it gets up to temp as quick as possible, along with the engine. Then it opens up to the oil cooler to stop it getting too hot. Makes sense.

 

I like to know how these things work when I'm trying to figure out a problem with them. I've suddenly got a more serious than the MPG issue, but I suppose it could be related to it; I have a coolant leak, but this is recent. I started a new thread about that, but this will help me a little to figure out where the leak is, whether it's isolated to the cold circuit or the whole system.

 

Once that's sorted, this understanding of the system is useful because I want to fit a coolant pre-heater. Defa produce some but none validated for this engine on the Superb, they say that is because of the stat between 6 and 7 for the DSG. This doesn't make sense to me though because you could install a pre-heater in the system in the position like the Webasto shown in this diagram is and heat up the cold circuit part of the system (exchanger - not that it'll do much without the fans blowing, and back to engine and the DSG. Defa said the problem was the stat doesn't open until it reaches 75C and there heater only goes up to a peak of 70C. Okay, so the DSG stat won't open until the engine runs it a little hotter still, but surely 70 at engine, exchanger and DSG and cold elsewhere is better than cold everywhere... I don't see the problem, but if you do then please let me know! Appreciate your help so far and very interesting (does that make me sad? Perhaps I need to get out more).

Edited 7 February, 2018 by snowathlete

[Ootohere]

?

Are you fitting the replacement water pump, and will you be fitting the pre-heater, or is it some technician with the gear and more than just an idea?

 

They might be best placed to advise you if you are using a VW Group trained technician to do the work.

[snowathlete]

1 minute ago, AwaoffSki said:

?

Are you fitting the replacement water pump, and will you be fitting the pre-heater, or is it some technician with the gear and more than just an idea?

 

They might be best placed to advise you if you are using a VW Group trained technician to do the work.

I don't know it's the water pump, that's just one suggested idea. It might be a damaged hose or something. Have to see. Won't do a big job like the water pump myself though.

 

The pre-heater we'd probably fit ourselves, it's not a hard job. But no rush because this will be for next winter now really.

[Ootohere]

You must have some skills then.

 

Not being cheeky i hope, but how long do you need to find out where the coolant leak is, and how are you going about doing it?

It really is not rocket science, or that difficult to  identify the cause. 

[snowathlete]

You must have great night vision Awaoffski, myself, I'll have to wait until the sun is up.

[Ootohere]

Sorry, thought you knew on Sunday and now Wednesday. 

No hurry then, the sun will come up tomorrow.