Originally Posted By: BMWTurboDzl
Originally Posted By: dbrowne1
People do commonly use non-spec oils in German cars. How much damage that actually does, if any, really depends on the particular engine, oil, and driving conditions.
For example, I ran M1 0W-40 and M1 5W-30 back to back one summer in a modified VW 1.8T and had both analyzed at 5K miles. Car saw probably 70-80 percent highway miles. Both oils did fine, very low wear metals across the board, no real differences. Certainly nothing to suggest that the non-spec, lower HTHS 5W-30 was causing any problems or excessive wear.
On the other hand, people who have used conventional or blend oils in the longitudinal 1.8T and followed what was at one time the recommended OCI of 10K miles, have had issues with engine sludge.
So I guess in the end, the safest route is to use a spec oil, but you can get away with doing otherwise if you have or gather enough information and perhaps do some testing.
The problem is that a UOA, esp a single pass, doesn't tell you whether or not the oil is "ok" for your engine. Even 5k miles UOA's.
My attitude is that the OEM's spec is designed for most of the markets in which they'll sell their cars and it meets the intended OCI based upon typical usage.
It actually tells you quite a bit, or at least it did in my case. The main concern with running a synthetic oil (that is otherwise a good product) that's below the specified viscosity and HTHS in an engine like the 1.8T is that it won't maintain a sufficient lubrication barrier when heated up and put under stress by areas like the turbo bearings and rod bearings.
So if a modified one shows wear metals that are indistinguishable from the same low numbers seen with "spec" 0W-40, while using the "non-spec" 5W-30, that tells me that there is no excessive wear in any of those areas as a result of using the 5W-30.
Change the test conditions and obviously that could change, but this car saw about as hard a life as one could create for such an engine without ending up in jail in North America.