I have something that has been bothering me for some time and that is the oil level on the dip stick. The dip stick is the code red so it is the correct one for my engine. There are no oil level markings on the dip stick. At least none that I recognize as such. There is a portion of the dip stick about an inch long that is "indented" not too far above the end. When I change oil, 6.5L, with a filter change, the oil level is way above the "indented" part. Does the top of the indentation mean add oil and the bottom mean you are in big trouble? What is the right oil level?

 

this car should take about 6 quarts of oil. check oil level and fill to the high mark. it should have two mark on the dipstick, one low and one high level. they are about 2 quarts different

 

Well, according to my owners manual the sump holds 5L (5.3QT), the oil filter 1L (1.05QT), and the oil cooler 0.7L (0.75QT) for at total capacity of 6.7L (7.1QT) or a nominal refill capacity of 6.5L (6.7QT). The dip stick has no marks on it that say "min" or "max". Only the flat indentation about an inch long and an inch or or so above the end. After draining the coil from the sump and the filter and refilling with 6.75QT, the oil level on the dip stick is over 1 inch above the top of the flat indentation. If I could post a picture, I suppose it would be more clear what I mean by a flat indentation. Anyway what is the correct level on the dip stick? I have to assume it is where the level is after I drain the sump and filter and add 6.75QT. To keep the discussion going, I use 5W-40 synthetic oil, Quaker State, and one bottle of STP for an oil change. I don't like the way the oil pressure drops with the engine at full operating temperature and the A/C running. the engine has approximately 200K miles on it. Yes, the oil pressure stays above the minimum without the STP, but just barely. I found out years ago from racing Alfa Romeo's that STP will lower the oil temperature when the engine is at a full operating temperature. We found about a 25 degree oil temperature drop under that condition. With the STP is have about 25psi at idle and A/C running. I live in Coastal West Central Florida and we almost never have temperatures below 32 degrees.

 

I was in error when I said that I was using Quaker State synthetic oil. That is in my Dodge van. I am using Shell Rotella synthetic in the 240D. I guess I read in another thread that Rotella is not really a synthetic.

STP is a polybutene which is routinely used by oil manufacturers as a viscosity index improver. I guess I need an explanation why adding STP would be harmful to the engine.

Does the oil cooler drain when I change oil or is that just trapped in there unless I open the oil filter drain plug?