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Old 05-03-2017, 00:16   #1
lleiro
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Dissapointing MPG at speed limit....

I had my Altea 1.9 TDI (BXE) for a few weeks now and already put some 1500 miles on it.

I bought for the known reliability and good MPG of the VAG 1.9.

I am however getting about 39mpg both on the computer and doing the math brim to brim.

That is driving exclusively at 70mph (per satnav on the M4 with flowing traffic and with the ocassional 75mph fro overtaking.

I was hoping to be around 55! I can get 40 on any petrol one.

I have since tried a totally different driving style and drove with a feathered right feet and kept the speed at no more than 65 and roughly at 2200 and now I got about 52mpg average on the computer which proved to be very accurate before. The problem is that driving like this is demanding, particularly without a cruise control.

I asked around and people are getting 55-60mpg on their PD130 with the 6sp gearbox (mine is 5 sp) and the altea in only 50kg heavier than a golf mk5. Could this be just aerodynamics?

There is two questions I would like to throw in here:

How much PSI you put on the OEM 205/55/16. I have them at 32 but I read that if I pump them up I can get better MPG.

Also (and I don't know the name of the part) the beginning of the airbox (the rectangle that is attached to the radiator so to speak) and connects wit the air box is all crooked and poorly taped with duct tape. So is the engine undertray. Loosely put together with zip ties.

Could this be having an effect?

Not particularly interested in a remap ot a tuning box unless there is enough people swearing by an improved mpg and even then, the increase of the insurance premium plus the remap would not be too cost effective.

I really would like to drive at 70-75mph with decent gas mileage. I can take the granny style most days but I spent too much time on my car to be concerned about keeping constant RPMs with the right foot.

Any pointers will be much appreciated!
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Old 05-03-2017, 10:17   #2
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The tray you mention that is taped together I'm assuming is your problem.

You should be seeing 55mpg easy at those speeds, do you hear any hissing noises? Especially on boost you should notice it, the intercooler connects to the airbox and it that's taped on you'll be losing pressure and getting a completely wrong fuel/air mixture.

I had a 110tdo ahf golf which was ridiculously good on fuel, would see 600 miles a tank regardless of driving style.


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Old 05-03-2017, 10:47   #3
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Thanks Ray. Do you know the name of that tray? Is actually the plastic piece in between the radiator side and the airbox assembly. I should take some pics so I get to the bottom of this. Probably there should be a part number some where in there

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Old 05-03-2017, 11:57   #4
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Found it!

It is the AIR INTAKE DUCT PIPE Part No 1K0805962A.

Do you or anyone still think this could be fouling my gas mileage?

I will replace it none the less but for learning purposes I would love to know.

Thanks!
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Old 05-03-2017, 16:56   #5
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since you haven't had it long I would check/change the air filter and fuel filter (do it every 20K not by the book I know, and don't trust the "it's just been fully serviced sir" crap) also at speed the under tray is pro'bly not helping I would sort that and go for a gearbox oil change too and a cabin filter which never gets changed unless you do it yourself
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Old 05-03-2017, 17:35   #6
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thanks! I did a full super duper service. All filters and oils changed. (Dont think included the gearbox oil) Paid like £195 which I never would have paid because I do the service my self usually but as soon as I bough it I went straight to the shop and got that done. I wasn't feeling to well to do all that outside myself. I already ordered the intake tray off ebay and will get it done as soon as I get it. Fingers cross I see an improvement there. Will have to have more time to sort the under tray. They sell a kit with all the pins and bolts for 9 quid I think. I should probably go for it.

Last edited by lleiro; 05-03-2017 at 17:38.
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Old 05-03-2017, 22:28   #7
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If that's just taped in and leaking air then the engine will be sucking more air in than intended ruining your mixture so it's almost a certainty to be doing something.

I would still keep looking around, check all the connections and hoses (helps if someone can rev it up so you can listen for any hissing noises, or drive by a wall with the window down, reflects the sound nicely) but yea you should see a nice difference once that is fixed.

If you want to tinker with your car there is a guy on YouTube who removed the injectors from his old Jetta, cleaned them all and the carbs and the car ran like new. Depends if you want a run around or something to take care of. Good luck


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Old 06-03-2017, 00:03   #8
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Quote:
Originally Posted by ray View Post
If that's just taped in and leaking air then the engine will be sucking more air in than intended ruining your mixture so it's almost a certainty to be doing something.

I would still keep looking around, check all the connections and hoses (helps if someone can rev it up so you can listen for any hissing noises, or drive by a wall with the window down, reflects the sound nicely) but yea you should see a nice difference once that is fixed.

If you want to tinker with your car there is a guy on YouTube who removed the injectors from his old Jetta, cleaned them all and the carbs and the car ran like new. Depends if you want a run around or something to take care of. Good luck


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Thanks! I can ask my wife to rev it up and look for some hiss. Maybe one day I tackle the injector too!
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Old 06-03-2017, 08:29   #9
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Just make sure it's in neutral.

Good luck man


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Old 06-03-2017, 10:32   #10
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good call!

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Old 21-03-2017, 19:24   #11
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I figured I would post an update.

I just changed my driving style and I am getting a consistent 49mpg with mixed driving and not doing more than 64-64 mph on the m4.

Could not hear any hissing and I did replaced the intake duct pipe and did not seem to make much of a difference.

I will do the liqui moly diesel purge next just in case.

I did notice quite a diffefence depending on the wind factor so I guess the car's coefficient plays a big role in the Alteas fuel efficiency.

In exactly the same route and with the engine at 90° sometimes I struggle to pass 49mpg in the motorway if windy whereas other times I manage up to 61mpg with the same driving style.

I guess I should not complain much and as a bonus there is an added calmness that comes from coasting at 63mph vs fluctuating between 70mph and 75+ and I am welcoming that too.

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Old 22-03-2017, 14:57   #12
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MPG varies a lot with driving style, as you have found out. The Altea is a good slippery shape, but does have a larger frontal area than the equivalent Leon, which will increase the drag.

Having the undertray fixed on by zip ties seems to be commonplace - the fixed nuts that are attached to the plastic side panels seem to gum up very quickly and lose their grip when you try to take the undertray off, tearing themselves out. This never used to happen on my old Toledo, so either the design of the nut has changed or the plastic material is less tough.
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Old 07-05-2017, 05:01   #13
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I don't know if this will help, but I'll mention it anyway. I recently had a failure on my 2.0 TDI 140 that caused it to lose power and put out a lot of smoke. It was eventually traced to an intercooler failure, which had been missed by the independent VAG specialist that I have used for over 20 years now. My hearing is shot so I couldn't hear a hiss, but it was very faint in any case.

Replacement of intercooler and the associated pipe seals has had a major effect on mpg - 10% improvement in all conditions, and the power delivery is much better too. It could be well worth checking the pressure side of your induction system (turbo - intercooler - inlet) for leaks. The seals do wear after the sort of mileage you (and I ) have on our engines, and replacing them can help. Also, the intercooler can fill up with oil out of the crankcase ventilation system, which is fed into the air inlet for emission control purposes (spit).

Last edited by Muttley; 07-05-2017 at 05:01.
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Old 11-05-2017, 22:15   #14
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I too have a 58 plate 1.9 altea and at 70mph average low 50s mpg. With the mileage on your car have you tried cleaning the egr valve of all the carbon build up? Might be worth a try if you have not. Noticed your car has the larger mfd screen has this been modified? As my car has the smaller version!
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Old 11-05-2017, 22:40   #15
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Really don't know whats the deal. I think I just go lucky. It has the oem bluetooth for the phone and I believe that that option requires the big MFD. I will be cleaning the EGR soon. If I do 70mph (per gps) I get ~42 mpg

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Old 11-05-2017, 22:43   #16
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Quote:
Originally Posted by Muttley View Post
I don't know if this will help, but I'll mention it anyway. I recently had a failure on my 2.0 TDI 140 that caused it to lose power and put out a lot of smoke. It was eventually traced to an intercooler failure, which had been missed by the independent VAG specialist that I have used for over 20 years now. My hearing is shot so I couldn't hear a hiss, but it was very faint in any case.

Replacement of intercooler and the associated pipe seals has had a major effect on mpg - 10% improvement in all conditions, and the power delivery is much better too. It could be well worth checking the pressure side of your induction system (turbo - intercooler - inlet) for leaks. The seals do wear after the sort of mileage you (and I ) have on our engines, and replacing them can help. Also, the intercooler can fill up with oil out of the crankcase ventilation system, which is fed into the air inlet for emission control purposes (spit).
Is this a diy project or a garage only? Im interested in this...

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Old 13-05-2017, 17:42   #17
Muttley
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A bit of both. Son and I replaced the actuator, garage spotted the intercooler leak and replaced that, then tuned the actuator (mainly by setting the total rod length to match the original, which we had kept).
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