A8OneDay

What is the best brand and weight oil for the engine, gas mileage and horsepower for a 2002 A4? Also, do any of those additives to the gas or to lube the engine really help? Is it worth consistently buying those products?

S4_Cinci (I S'edTFA)

engine and are willing to spend the $, go synthetic for sure. I have used nothing else on my vehicles since '95. Look at the ratings on the oil container, specifically looking for the ACEA specs it meets: A1 is for fuel economy, while A3 is for engine wear protection.

5w-20 or 30 and 0w-20 or 30 give the best fuel economy, but something like a 0w-40 provides for better wear protection at the expense of some fuel economy. The reality is maybe 0.5 mpg difference, but for CAFE purposes if you are a manufacturer, the trade-off is worth it.

If you are looking to save $, then dino oils are pretty good these days, but I would only use dino oil in an older car that is high mileage, e.g. a "beater". If you use quality oil, additives are not necessary. I still use fule injector cleaner every 6 months or so, but in reality, that likely doesn't provide any big benefit.

Oil brands I like are Mobil 1 (for a good value) or Valvoline Synthetic; for more $ you can go Amsoil or Motul or Elf. Castrol Syntec is OK as well, but there used to be German made varieties of this sold here, but that has stopped and the consensus is the US made stuff is not as good. In general, the US oil specs are not as stringent as the european ones. I also like to change the synth at least every 5k miles - I value protection over economy to the point of likely wasting some $, but oil is cheap compared to gasoline. Follow the owner's manual and you can't go wrong for weights, but I always have a 0w-40 in my 2.7t engine during winter, for sure.

Chalfont

but change it regularly
<img src="http://pictureposter.audiworld.com/60660/imgp0885.jpg">
almost every 2,000 - 3000 days !

JmuRiz

Where's the best place to get Mann oil filters?

S4_Cinci (I S'edTFA)

there are also some decent parts places that will sell the Mann filters (I also like the Mahle ones as well) - I've used carmadillo.com with good results, also thepartsbin.com

There are also Audi/vw dealers that sell them on the web - a decnt price is $9-10 ea; less if you buy a mult-pak. Some places will ship for free if you order over $50 in merchandise - and that's easy to hit for these cars!

GeoW97

...works great for me; light in the cold but holds up climbing the 5200 feet to my house in 100 degree weather. As to your question about oil additives, I have to pitch Auto-RX, which is a 3,500 mile engine-cleaning regimen that worked wonders on my '99 A6. You put it in for 1,500 miles (it's actually a form of metal polish) in regular dino oil, then do a 2,000 mile "rinse cycle", again with dino oil, and it took my somewhat sluggish and creaky engine and gave it back its *****...