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Valve noise and oil/filters

In my '87 5000CSQ, I had slight valve noise at cold start-up as others
have mentioned. It reduced considerably when I switched to synthetic oil
(Mobil1, 15W-50) and was audible only the first few seconds after a
cold-start. At this juncture I was using a Fram oil filter. The last
oil change, I decided to try the genuine Audi filter ($14). For the
87-on turbos, Audi got rid of the main-filter + separate-turbo-filter
combination and has only one special turbo filter. According to the
dealer's parts person, this filter is the same size as the main filter
but has "different valving". I found something interesting when I
installed this filter. Usually, I fill the filter with oil before
installing on the car so as to avoid oil starvation on start-up. 
When I tried to fill this Audi turbo filter with oil (through the
large threaded hole in the center), no more than a couple ounces
went through before it filled up! I guess it was the anti-drain-back
valve preventing the oil from going in. I had never witnessed this
phenomenon in other filters (AC-Delco, Fram, Mitsubishi, etc) that I
have used. Have any of you seen this before? Of course, I filled the
filter with oil through the smaller holes on the periphery of the
filter and installed it.

	Since I have installed this Audi filter, I don't recall hearing
any valve clatter on cold start-ups. But I wasn't looking out for it
either - so I might be mistaken. I will watch out for the valve noise
and report my findings. But an oil filter with an anti-drain-back valve
has to be better than one without since it prevents the oil in the
passage-ways above the filter from draining back into the filter and
so the oil has a lesser distance to travel on start-ups. I also
noticed when I removed the oil filter from the car, that a considerable
amount of oil flowed out of the vertical tube (that the filter threads into)
after I unscrewed the filter off the last thread. This implies that,
even after I had half removed the filter, exposing the gasket, the oil
didn't flow through the filter, out the small holes in the periphery.
The anti-drain-valve was holding the oil up in the vertical passage-way.

	Previously, I had presumed that anit-drain-back valves were
useful only in applications where the filter was horizontally mounted
so as to prevent oil from flowing out of the filter into the crankcase
pan. But my experience shows that it helps even in vertically mounted
applications (as in the Audi). Any thoughts on this? 

Zafer Mehmood