BIG difference in oil color Duramax LBZ vs LMM...

[Ponch]

I noticed a HUGE difference in oil color between my duramax LBZ engine VS my father's LMM engine. I am surprised at how fast his LMM engine can darken oil with the larger EGR system verses my LBZ motor (with EGR disabled) in just a few thousand miles! I am not new to diesel engines, and I know that diesel engines turn oil dark very quickly by nature...BUT even before I disabled my EGR system...I do not recall my engine turning oil as dark as his very quickly. I also know that you cannot "judge oil by it's color"..BUT I think it would be safe to "assume" that any oil in my LBZ motor should last longer TBN and oxidation/nitration wise if I am not mistaken?? Is it safe to say that pre LMM engines can live longer oil life without the engine recirculating exhaust back into the engine? I am talking BLACK TAR SPRAY PAINT looking/nasty smelling oil after roughly 8,000 miles....and he still had about 25 percent "oil life" left according to his oil life monitor. He also was running rotella 15w40 CJ-4 oil..but I doubt that oil type would make a difference. I look forward to "dnewton3's" response to this..as he has the same type of vehicle/engine combo. -PONCHO

 

[Bambam]

By-pass the PCV system and keep even more gak from building up in your intake! Not sure if it'll keep the oil any cleaner,but your engine will thank you for it! It's about a 45 minute install!

 

[A_Harman]

Yep, the EGR really junks things up. That's why the CI4+ oil specification was created when EGR engines first came out. More dispersancy, higher TBN, more zddp; all necessary to deal with the effects of putting higher soot in the oil.

Ultra-low sulfur diesel has come along since then, reducing the need for 12+ levels of TBN, but dispersancy is still very important. EGR engines will turn the oil black quickly, but the high detergency is designed to keep the soot in suspension throughout the OCI. If you disable EGR, you could probably go past the OLM, but then you would need to do oil analyses to know when to change oil.