A question was asked about dark colored oil on a G35 board and this was one of the responses:
quote:I've never read this type of feedback over here and wanted to know what bob's regulars think. Is there validity in his explanation? His response mentions crankshaft bearings being the first to suffer from dirty oil.. and I've had relatively high lead wear in my G35, so I was thinking that this statement would apply in my case... Should I believe it?
Q45tech (Registered) 06/12/04 10:10 AM Depends on the sizes of the dirt particles. Oil analysis doesn't measure particles as to size. Experiment just change the filter if the oil cleans up some in 50 miles you know! The G35 filters are tiny and have a limited hold capacity, this is the limiting factor not the oil stability. Why Nissan warns for longest engine life change every 90 days. What they are saying is if you want the engine to perform well at 200,000 miles follow this interval. Those that are leasing or care nothing for future owners can get by with 6 month  changes. "A cold start can also be a dirty start, because of the oil pressure-release valve in your oil filter. If the oil pressure is too high (say, if the oil filter is clogged up, or you have thick oil), this valve opens, and unfiltered oil enters the oil circuit of your engine. The crankshaft bearings usually get their oil directly from the filter, and so they usually suffer first. " http://www.baldwinfilter.com/engineer/pdf/89-5r.pdf http://www.websorcerer.com/GeekOut/ http://www.baldwinfilter.com/engineer/95_11.html A 25 micron filter will only filter 0.001" and the G35 bearing clearances mean you need to filter to 8-10 microns or better. Compared to some domestic which may have 50-60 micron bearing clearances. http://www.shoclub.com/lubrication-oil/lubrication-oilpart6.htm Every time you exceed 3,000 rpm the oil pressure rises to the bypass point and unfiltered oil get circulated, as the filter gets dirty the rpm bypass point gets lower and lower. People that do lots of high rpm cruising, run into this problem in coolish temperatures.