I have a A6 C6 2005 with the 165kw 225hp BMK 3.0 TDI engine for almost 2 years now. A month ago with the colder winter temperatures I started to have the issue with getting a low oil pressure warning on the first morning startup. If i leave it it will go away after about 20-30 sec (Its the digital gauge and warning so I guess thats the minimum time for it, I do not have a bulb for the pressure) , and If i turn it off and crank up, there is no warning. I also had 2 times when I did some really agressive driving with a hot engine to get the low pressure warning for a few seconds, but as soon as I let off the throttle a bit it goes away.

I have since put brand new motul syntethic 5w40 oil and new filters just to make sure its not the oil or clogged filter. Still get the issue in to morning, and did not have the time to see what happens when i take it for a longer and more demanding drive.

Also i have the standard chain rattle on first start till it builds up pressure in the timing chain tensioner for 5-10 sec.

No other issue with the car, not burning oil, not overheating.

Should i worry about it or just be fine with it needing some time to build up pressure with the thicker oil in the winter ? My mechanic that does only VAG cars said he has a few with the same issue in winter and its fine for older cars ?

 

And I forgot to write in the first post, I have changed the oil pressure sensor on the oil filter housing with a brand new one, so its not the issue

 

I'd pull the owner's manual, or look it up online to see which VW oil spec rating is required for your TDI engine, as well as the recommended weight of oil for that particular engine under 'normal' climate conditions. If you find the standard fill is a 5W30 for your motor, verify the VW oil spec and be sure whatever oil you buy meets that oil spec, etc.

The emissions-TDI engines like I have generally run a synthetic 5W30 from factory, with alternative weights, such as 0W30 or 5W40 listed for use in more extreme climate zones, etc. In recent years, VW/Audi have begun selling the 0W30 synthetic rather than the 5W30. Tried it once and really didn't care for it; lots of noise. I buy the Liqui Moly 5W30 (Long-LIfe 4200; meeting VW oil spec 507...this oil spec is designed specifically for emission control systems equipped TDIs to prevent clogging up these expensive systems).

Today was very first time I've started my 2010 CATA engine, 3.0L TDI in 10 degree F ambient temps, and although a bit slow to crank at this low temp, it started fine. Not sure how it will fare as the temps continue to drop to -10 and -15 degrees F overnights and topping out at 0 or 3 degrees F in daytime hours (an Arctic, bomb-cyclone from Canada currently modifying our Winter temps by a considerable measure), but normally the 5W30 works best for the 'Goldilocks' climate range/region I'm located in...not too hot, and not too cold.

Definitely research what is correct for your engine.