Colour of the engine oil is not the correct measure of its effectiveness, infact its holding combustion impurities well if your engine oil colour becomes brown its doing its job correctly. Engine oil flush not at all recommended even at 2 lak km. Change engine oil at regular intervals just before manufacturer specified time limit.
-suryaputhra
-suryaputhra
Like you said, the oil holds combustion impurities but also, fine mteal fragments from the liner & piston rings as well as the soot from its own degradation. When the oil is drained, some impurities are left behing in the passages & sump. If you refill without flush, these enter the new oil & reduce its capabilities to do its job. Thats why the suggest to flush. Basically, during flush, they put in some cheap oil & run the engine to let it pickup the residue. Then they drain this oil & put in new oil as per manufacturer standards & filter.
Based on the running of the car, engine flush needs to be done. My preowned WagonR did not have complete service history, so i flushed it at 40k service & the engine became appreciably smoother. In mt Swift, i did the flush at 10k but i hadn't used the car too much so didn't notice much difference. But my oil remained yellow till i sold the car 4 months later at 15k km
Ameyam