About to top up your oil? STOP!! Read this first.
Use only FULLY synthetic oil and never EVER top it up with any other kind. - it is said by many oil experts that mixing of synthetic oil with any amount - even a trace - of mineral oil causes the synthetic oil to break down and form black sludge - and vice-versa.
Audi should put on bright red letters on the engine saying "FULLY SYNTHETIC OIL ONLY!!! USE OF ANY MINERAL OILS WHATSOEVER WILL CAUSE EXTENSIVE ENGINE DAMAGE!!!"
Most people eventually notice the oil is a bit low, and buy halfrauds or petrol station oil and dont know what kind it is, then top up the car and later it goes bang. It came from the factory filled with fully synthetic and must remain that way!
FULLY SYNTH ONLY AT ALL TIMES if you intend to top it up, or if you get a service / oil change done at an indy, make sure they know this too!
My indy dealer did an oil change using mineral oil, and the traces of synthetic in the system were enough to cause the start of sludging up, a flicker of the oil light occasionally and blackening of the oil showed this to be happening in just 3000 miles.
I poured wynn's engine flush in the motor, then when it was at operating temp I revved it at 2k rpm for 15 minutes (wynns recommendations for full cleaning) and then switched off and dumped the VERY hot oil into a steel container under the car, letting every drop escape before fitting a new oil filter and filling up with 4L of fully synthetic oil at £36 from a motor factor, It doesnt have to be dear, but it DOES have to be fully synthetic. Wear thick waterproof gloves! That old oil will be at about 200deg c. - it has to be dumped hot so it is thin enough to drain completely. I will flush and refill it again at the soonest opportunity so that it is clean and golden and the engine should last a long time.
If you top up or otherwise use normal oil of any other kind and keep running the car, you will get a blown engine in the end....its just a matter of time.
If you have the dreaded oil pressure light already, and your dipstick shows between min and max, then stop using it and get it flushed right away.
The full article I read was from industry experts in motor oil, and I could dig it up for you to read, but take it from me, it is serious.
Hope this helps.