Cause of poor mpg

[A4donkey]

Just want your inputs , so that we can have a check list to follow;
Assume the driving habit remain unchange.
1) Aged engine oil
2) Flat tyres
3) Dirty air filter
4) Heavy loading
5) Ambient temperature
6) Faulty PCV ( Some said so, but not sure!!)
7)
8)
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[Pr0n]

heavy foot.
switching gears later in the RPM band.

[Affinitive]

Far too often, "dragging" or faulty brakes are overlooked or dismissed as a possible and/or actual issue . But yes, poor maintenance in general is also a common issue.

There was another guy on the forum here who's being blown off by his dealer with poor mileage concerns. Just something to consider and also check, here it goes - I fairly commonly see 1.8T's where the water pump impellar shaft will start walking itself into the pump housing. For some reason, some dimwhit engineer thought it great to use a spring on the pump shaft. I guess the idea is to always maintain a bearing "preload" on the pump bearings as the bearings develop wear and tear as age and mileage take their toll. What happens is the pump pulley will start to rub on the pump housing and as crazy as it sounds, it gets to a point where it even affects staring quality and overall mpg since the pump will put too much "load" on the engine. I see it mainly on 02 - 04 1.8T's in cars. I think it has something to do with the particular bearings supplied for the pumps produced during this production range. I always replace the pump with metal impellar aftermarket pumps which do not have the stupid srpings. Though in general, I have seen similar issues in the past where belt driven components were failing putting too much load on the engine.
Essentially what it boils down to is to monitor engine load calculations on the engine when the car is not actually being driven, i.e. -idle and cruising rpm. Unfortunately, load calculations are not exactly the same on all equivilant cars with identical equipment options. Far too many variables to consider but in general, the load calc's should be fairly even from one car to the next with all the same equipment options.

Sooooo, I guess what i'm saying/adding to the list is : mechanical issues.

Alright, let the thrashing begin...............LOL

C

[scorneil]

boost leak
faulty oxygen sensor

[diztek]

worn suspension. fuel filter. spark plugs. coilpacks.

[G Men 08]

deffinatley coil packs spark plugs and air filters.. i jumped 5 mpgs when i replaced those.. just replaced my fuel filter so hopefully that will help too!! 3.0 gettin about 24 mpgs before the fuel filter change FTW!!

[Splattj]

Dirty Mass Airflow Meter (MAF)

[pondside36]

Affinitive... I haven't examined our water pumps but I do know that a very common mechanical seal for water pumps of varying size use a spring to keep pressure on the rotating seal (often carbon) and stationary seal. Is this the spring you are speaking of? If so this shouldn't have any affect on bearings shifting.. that would be more of just a bearing failing, say for the pully. Just my .02 cents..

[Affinitive]

I think I know what you mean and no, I believe we're talking about two different springs. The spring I mention can be seen when you take out an OE pump and look at the plastic impellar. Behind it, I should say, is a fairly big coil spring which will apply pressure on the pump shaft pushing it inward into the block. I don't know if it's just the bearing developing play or if it's the whole bearing that's not pressed into the pump housing tightly enough and in turn slowly moves over time.
I wish I could post some pics.
The spring you mention on seals, inside the inner portion of the seal lip. That wouldn't apply any lateral pressure on the pump shaft.

C

[pondside36]

^^^ oh ok.. now I know what you are saying.. I was just trying to get my head around your description of the water pump... I just slapped the new metal impeler one in on my TB job and called it a day.. I'm going to check it out this weekend when another guy does his...

[woofster]

I just changed my spark plugs (at the scheduled maintenance interval) and immediately I noticed my fuel consumption decreased dramatically as a result. The old spark plugs did look pretty tired but they were changed according to the owner's manual. Goes to show, sometimes you need to do your own assessment beyond simply following the manual's recommendations!

[A4TL]

right vertical pedal
ethanol content
heat
crap gas (check CF's!)

if you think otherwise, put your car on cruise @62mph for about 4 hours and be amazed at how high your mpg is (engine steady state low load) mostly flatlands area.

[DZA]

It was rather boring that week, but I went a full tank without shifting higher than 2000 rpms. I don't remember the math but I managed 50+ additional miles on the tank.