I have a CAPS era Cummins ISL 8.9L in my motorhome. It's pushing 35,000 - 36,000 pounds down the road. I ran Chevron Delo 400 LE 15-40 before but now I'm using Chevron Delo 15-40 SDE. This is a CK4 oil. I haven't done anything else different. What I'm noticing is that under high load - i.e. pulling a long, steep grade - the oil pressure falls below what I previously experience before using CK4. It seems to be a temporary viscosity loss as the oil pressure rises again after the engine load decreases and operating temperature drops.
Yesterday in 100 degree ambient temperature going up grades to Payson, Arizona my coolant temperature reached 205 degrees and the oil pressure at 1,500 RPM dropped to 30 - 35 PSI. At the top of a long grade at a stop light the pressure fell below 10 PSI at idle. When the coolant was at the normal operating temperature of around 182 degrees, the oil pressure at 1,500 RPM was back to 40 - 45 PSI and at idle it was 14 - 15 PSI. Is this normal? The older LE formula never dropped this low. It has happened since changing to CK4 two oil changes ago and has happened repeatedly with CK4.
Yesterday in 100 degree ambient temperature going up grades to Payson, Arizona my coolant temperature reached 205 degrees and the oil pressure at 1,500 RPM dropped to 30 - 35 PSI. At the top of a long grade at a stop light the pressure fell below 10 PSI at idle. When the coolant was at the normal operating temperature of around 182 degrees, the oil pressure at 1,500 RPM was back to 40 - 45 PSI and at idle it was 14 - 15 PSI. Is this normal? The older LE formula never dropped this low. It has happened since changing to CK4 two oil changes ago and has happened repeatedly with CK4.