Oil Consumption + pressure ['90 100Q]

[brooks@fortnet.org (Brooks Ellis)]

	I have been noticing, that lately my car has been consuming more than it's fair share of Oil. It will take about a half of a quart in about 500 miles, although sometimes less.
	It will generally, not drink any oil for the first 1000 miles after an oil change, ( ie the oil is up to the top of the textured part of the dipstick ) but after that, it will drink oil, and if I keep adding it, it will keep drinking it unless I let it stay at about half of the textured area. It will then hardly touch the oil.
	Could this be something to do with the synthetic 5w50 Penziol ( or sometimes 5w50 castrol syntec ) that I am running? It is a really wierd phenomina. I used to run dino oil, and it would hardly touch the stuff. Now, if I top it off, it will keep drinking it.. very odd. 
	Could this be due to the non-OEM filter? ( I am sure that soon, the Audi gods will cause me much pain and anguish for going to Jiffy Lube.. Sorry audi-gods!!! Take my first born son as a sacrifice to appease your anger! ) I know that it may not function exactly as the stock one.. Thus when my car sits there, the oil looks right, but may be over filled? Thus, too much pressure, and it would suck a little oil until it is at the right point.
	I try not to push my car very hard at all - I hardly press it until the oil temp and engine temp are about 1/2 way to normal, then I will not press it hard until the Oil and engine temp are all the way up there. Every so often, I may pull out into traffic when it is cold, and have to punch it to not get hit.. Yet this doesn't seem to have an effect on it, at least not in the short term.
	I live at the top of some hills on the front range of colorado, and do not need to use the gas too much to get to the highway a few miles down the way. If I take my foot off the gas to let the engine brake me when it is cold, is it possible that the vaccum and cold engine together will let oil be sucked into the combusion chamber, thus causing it to burn oil? 
	I have never _seen_ it burn oil, meaning that the exhaust looks perfectly clear. could hot temps by racing ( rally style!! true to the Audi name! ) up my dirt road cause anything like this? I do not notice any oil on the floor of my garage, and this is why I am assuming that it must be burning it.

	<geez, this is turning out to be a long post!!>
	On a related note (?), I notice that after an oil change, I get 4.5-5 bar oil pressure constantly, and about 2 or 3 under idle conditions. Over time, even though the oil is kept full, the pressure will slowly decrease to about 4 bar, and sometimes even less. Now, it is usially about 3.7 - 4. ( under full throtte, it will increase of course, enough to cover the RPMs I run ) 
	Why does this happen? Does it happen to anyone else? I think it is super wierd. My car is finiky about the oil it runs also, if I run 10w30 or 5w30 it will sometimes have super low oil pressure (2-3 bar..!!). 
	
So what do you guys (and gals? Never noticed any quattro-ladies, but I might as well be politically correct.. yuck) think about this situation? It is something to worry about? Should I have a compression check done to make sure the cylinders are not leaking? Should I use a heavier or lighter weight oil? ( the 5w50's will naturally act more like a 50 weight oil than a 5.. ) 
do I have an oil leak that only happens under high pressure? I have hit some pretty good sized rocks in my time, and I don't think they caused any damage, but you never know - maybe a small, small leak that only manefests itself when the oil is thin, and/or under high pressure.. due to heat, old oil, etc..

brooks   '  My messages are always super long. I should be more concise '