Valve Cover Replacement and better mileage?

[tractoman]

My kid was home from college for a couple weeks and I have been suspicious of his valve cover leading to oil consumption.
Car is a2008 A4 quattro, 2.0 FSI with 206K miles on the clock. I replaced his valve cover and gasket and replaced the pcv gasket, cam follower and did an oil change.
On his way back to LA the other day he tells me he got way better mileage. He would normally drive 330 miles on a tank and stop for gas at the same place each trip. The DIS would say he had 15 miles to go to empty. He's done this drive about 6 times before. Same experience each trip.
This trip, he drove 345 miles and when he stopped for gas, the DIS said he had 90+ miles to empty.
Is this even possible?
He filled up at the gas stop and it took about 12-13 gallons so he was definately not on empty.
Could the new valve cover increase mileage? I've done the follower and oil changes before and did not get this mileage increase.
It's like his car has gone from 20 or so mpg to almost 28mpg.
I cannot think of a good reason the valve cover could cause this outcome.
Glad to get the increase though and hope it's not a fluke.

[Theiceman]

well lets see how repeated reading look.

[wangerang]

Potentially the fuel level sensor is giving funky readings? Mine likes to give different readings on miles til empty almost every drive.


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[Jay-Bee]

Valve cover and PCV gaskets can cause some large air leaks, sounds right if it's been leaking a while. Fuel trims are now where they should be.

[tractoman]

Valve cover and PCV gaskets can cause some large air leaks, sounds right if it's been leaking a while. Fuel trims are now where they should be.

No CEL for a couple years on his car though but it always seemed to get crappy mileage for a 2.0.

[tractoman]

Potentially the fuel level sensor is giving funky readings? Mine likes to give different readings on miles til empty almost every drive.


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But when he filled up, the amount of fuel it took supported the DIS reading. I think these cars hold about 16 gallons correct? He filled up with about 12.5 gallons.

[Jayz691]

330-340 mile per tank is really low. I get around 400 with a k04, and using a little e85. Stock should be 420-440/tank. If ya had some leaks prior, that was throwing your fuel trims/correction off, could have been killing your milage.

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[tractoman]

330-340 mile per tank is really low. I get around 400 with a k04, and using a little e85. Stock should be 420-440/tank. If ya had some leaks prior, that was throwing your fuel trims/correction off, could have been killing your milage.

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Could it run OK and pass smog and no CEL with these sort of leaks?

[Theiceman]

Who knows what oil laden air does to combustion mixture... If you had a cracked cover you were injesting way more oil vapour than designed. Could even been fouling plugs somewhat, giving poor gas mileage.

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[Jayz691]

This[emoji115] is kinda what I was thinking, and air leak in the internal chambers. I believe I read somewhere the affects that oil vapor has on octane rating of fuel. Could have been a sales pitch, idk. But If its not running optimal, its gonna have poorer gas milage.

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[Brillo]

Oil mist (and small amounts of diesel fuel contamination for that matter) can dramatically lower the octane rating and cause timing to be pulled which will gas milage. Minor air leaks can have the same effect. You might monitor your oil consumption to see if it is lower with the new VC. The new cam follower should have no gas milage effect unless the one replaced was significantly damaged.

[80sGuy]

Mine usually show 450-500+ miles on a full tank whenever I drive to and from Vegas. I can go on with one fill from L.A. to SF vice/versa.

https://live.staticflickr.com/1914/43824686350_43caab0563_c.jpg

[Jayz691]

Mine usually show 450-500+ miles on a full tank whenever I drive to and from Vegas. I can go on with one fill from L.A. to SF vice/versa.

https://live.staticflickr.com/1914/43824686350_43caab0563_c.jpgDamm ! I've never had higher than like 440mi. But I don't drive very easy, even when it was stock, lol.

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[PhireSideZA]

Gosh, this thread is making me feel like my car is way off. I think my best tank has been 450 kilometers/ 280mi[confused]

[Jayz691]

Gosh, this thread is making me feel like my car is way off. I think my best tank has been 450 kilometers/ 280mi[confused]Yeah, thats pretty bad.. I average around 350-380 now, k04 with a few gallons of e85, which lowers mpg. You are using premium, right?

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[PhireSideZA]

Yeah, thats pretty bad.. I average around 350-380 now, k04 with a few gallons of e85, which lowers mpg. You are using premium, right?

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My car is a basket case so I expect the usage to be a little on the rough side. We only get 95 octane here in South Africa, not that our fuel is what I would consider to be good quality, but I digress.

Besides that it is stock - the only thing different on mine is that when I got it, it was missing an entire SMIC which was just bypassed with a piece of metal pipe. But other than that, no tunes, stock K03 turbo, stock HPFP, oh and I had the car decatted and had a test pipe fitted.

[Charles.waite]

I get between 17-19 city mileage, really depends on how much highway driving I do. My best ever mileage (according to my Fuelly logs) is 29.5.

Mileage can vary a TON based on type of driving you do and the topography. Seattle is super hilly, and I live in the city so lots of stop signs, traffic lights, crossing busy streets (you have to really give it the beans sometimes to shoot across 4 busy lanes going 35-45mph...). My wife's old Q5 2.0t didn't get much better mileage. Our current Q7 3.0t gets far worse. Tracking MPG over time gives you a decent picture of mileage and can help point towards thins being off, but in general you can't really compare mileage between different drivers in different cars in different places.

I'm pretty sure most people here don't cruise at 75-85 on the highway and pass fairly aggressively like I do, so personal driving style plays a big factor. Not my fault Seattle drivers are mostly braindead, camp in the left lane, incapable of thinking more than one car ahead of themselves, and absolutely terrified of passing in general.