Rotella T6 is not recommended for the 3.0 EcoDiesel due to issues with turbo coking. It's a general caution against using heavy-duty diesel oil in a light-duty diesel engine.
Initially, the EcoDiesel was filled with Shell ECT C3 5W-30 (PP Euro L 5W-30) straight from the factory. However, installing an engine designed in the pre-DPF era for GM sedans intended for the European market into a full-size pickup truck led to several problems. For instance, under heavy loads, the first generation EcoDiesel experienced crankshaft flexing. Moreover, the EGR system was clogging the intake with soot, while the DPF was creating excessive backpressure.
FCA (Fiat Chrysler Automobiles) was quick to address these issues, with motor oil being the apparent low-hanging fruit. Unfortunately, Rotella T6 proved ineffective within the engine’s tiny, overheating turbocharger. It also failed to manage the substantial soot levels, which polished the bearings to the color visible in the pictures posted by
@RDY4WAR. Ultimately, FCA settled on recommending a full-SAPS European motor oil with strict OEM approvals, thereby creating their somewhat redundant MS specification - 12991. This specification includes oils such as QS/PP Euro 5W-40, Castrol EDGE 5W-40 (SP), and similar products. Indeed, FCA’s situation with the EcoDiesel was desperate, leading to the recommendation of a full-SAPS Euro oil for diesel engines equipped with DPF and SCR systems.
Mobil, on their part, has provided guidelines on how to use their full SAPS 5W-40 (Mobil 1 FS 5W-40):
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FCA is presumably hoping that by the time the oil starts contaminating the aftertreatment system, the vehicle will have surpassed its warranty period.
Moreover, viewing a 3.0 EcoDiesel without its engine cover reveals a rather chaotic scene, a testament to its initial design in the early 2000s by VM Motori and the subsequent passing of the project between various engineering teams.
If Stellantis hadn’t already terminated 400 engineers in the US, with plans to lay off another 3200 soon with the intention of relocating those jobs to India and Mexico, perhaps we could seek further insights into the EcoDiesel’s development. Nevertheless, it seems the EcoDiesel will be revisited by a new "elite team" based in Mumbai.
We've managed to run a D60 for 1.5 million miles using Rotella T4 before switching to Delvac 1 Extreme. While Rotella may not be the pinnacle of engine oils, many criticisms leveled against it may be unwarranted.