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Temporary Viscosity Loss #5418750 05/01/20 08:59 PM
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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.


Alpine Coach 40MDTS Cummins ISL 400hp
1972 MG Midget - Nissan A15 engine and Nissan 60 series 5-speed
Re: Temporary Viscosity Loss [Re: Koop] #5418770 05/01/20 09:24 PM
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Do you have an oil temp gauge?

Re: Temporary Viscosity Loss [Re: Koop] #5418775 05/01/20 09:37 PM
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Yep, the old stuff was thicker with a KV110C of around 15.6 and HTHS of 4.3-4.4 @ 150C. Many of the new 15W40s have lowered their KV100C to the mid 14s. Maybe it's a fuel economy thing.

I've been known to spike my 15W40s in hot weather with 20% SAE 50. History tells us that back in the day, 15W40 was a wildcat grade. Truckers mixed SAE 50 with 10W30 to get a thick multi-grade.

Re: Temporary Viscosity Loss [Re: ripcord] #5418800 05/01/20 10:19 PM
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Originally Posted by ripcord
Do you have an oil temp gauge?


Unfortunately, no.


Alpine Coach 40MDTS Cummins ISL 400hp
1972 MG Midget - Nissan A15 engine and Nissan 60 series 5-speed
Re: Temporary Viscosity Loss [Re: Koop] #5418898 05/02/20 05:20 AM
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I would go with Chevron Delo XLE 15W-40 - KV100 of 14.9 vs the standard Delo SDE 15W-40 KV of 14.2 (both CK-4)

The XLE is also regularly about the same price as the standard SDE. $12.53/gallon right now (actually cheaper than the SDE!)

https://www.walmart.com/ip/Chevron-...N-Advanced-Technology-1-Gallon/464559459

Re: Temporary Viscosity Loss [Re: Koop] #5418950 05/02/20 08:33 AM
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The Cummins is an expensive engine I would first contact Cummins rather than a use forums opinion.?


2015 F150 2.7
2018 F350 6.2
Re: Temporary Viscosity Loss [Re: Koop] #5420378 05/03/20 11:02 PM
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I doubt it's the oil. Delo SDE is pretty thick. By the way the oil pressure is determined by HTHS, not KV100.

Delo XLE has more VII than Delo SDE; therefore, it would perform worse. I would only use it if I was doing an extended an OCI.

Estimated base-oil viscosity (BO DV150) and VII content of selected oils


2020 Toyota Prius Prime XLE plug-in hybrid, 2ZR-FXE engine, ~ 65 mpg on regular gasoline, ~ 5,000 mi
TGMO 0W-16 SN/RC Japan
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Re: Temporary Viscosity Loss [Re: Koop] #5420836 05/04/20 02:05 PM
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I always thought that oil pressure followed the bulk oil (sump) viscosity. As the temperature rises, the oil pressure goes down.
On a cold winter morning, the oil pressure is off the chart.

Re: Temporary Viscosity Loss [Re: userfriendly] #5420927 05/04/20 03:51 PM
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Re: Temporary Viscosity Loss [Re: Koop] #5420988 05/04/20 04:57 PM
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OMG - the "CAPS" system! Cummins Accumulator Pump System. Cummins quickly got rid of that thing. Hope it is hanging in there for you. Don't know Delo oils, but sure seems to be a temp / vis thing with CAFE fuel economy. Have you checked the other major supplier's vis / temp data?


Elastohydrodynamic Lubrication makes the world go 'round!
2017 Ram 2500 - PUP 0W-40, Fram XG
2011 Chev Traverse - PUP 5W-30, Fram XG
2005 Chev Kodiak C5500 - PUP 10W-30, Fram XG
Re: Temporary Viscosity Loss [Re: LubricatusObsess] #5421112 05/04/20 07:35 PM
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Originally Posted by LubricatusObsess
OMG - the "CAPS" system! Cummins Accumulator Pump System. Cummins quickly got rid of that thing. Hope it is hanging in there for you. Don't know Delo oils, but sure seems to be a temp / vis thing with CAFE fuel economy. Have you checked the other major supplier's vis / temp data?


Yeah, the lift pump is definitely a weakness in CAPS, but otherwise the engine is solid. No EGR or other crap. Thanks guys for the responses, I'm still trying to get my head around HTHS and why this oil performs differently than the previous CJ-4 Delo 400 LE. I haven't been able to find a HTHS spec for the CJ-4.


Alpine Coach 40MDTS Cummins ISL 400hp
1972 MG Midget - Nissan A15 engine and Nissan 60 series 5-speed
Re: Temporary Viscosity Loss [Re: Koop] #5421205 05/04/20 09:20 PM
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Originally Posted by Koop
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.


I’ve also noticed a slight drop in oil pressure with the Series 60 Detroit in my Semi while I’m loaded heavy and pulling a grade. Once my engine is no longer pulling the grade, and the coolant temperature and the oil temperature cool back down to normal temperatures, my oil pressure gauge reads the same as it was reading before I pulled the grade. I’m guesstimating I see maybe a drop of 2 to 4 pounds on the gauge when pulling a grade.

I’ve seen this regularly using the following 15W40 motor oils: Mobil Delvac 1300 Super CJ4 and CK4, Chevron Delo 400 LE CJ4, Chevron Delo 400 SDE CK4, and Chevron Delo 400 XLE CK4. I’ve never been overly concerned about it, I’ve always assumed the slight oil pressure drop is in relation to the hotter engine oil temperature while the engine is working a bit harder, pulling a grade.

And for what it’s worth, I didn’t notice this change in oil pressure nearly as much when I used Phillips 66 Guardol ECT 15W40 in my engine. That oil really seemed to keep a consistent oil pressure, even when I was climbing a grade.

Re: Temporary Viscosity Loss [Re: userfriendly] #5421209 05/04/20 09:23 PM
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Originally Posted by userfriendly
I always thought that oil pressure followed the bulk oil (sump) viscosity. As the temperature rises, the oil pressure goes down.
On a cold winter morning, the oil pressure is off the chart.


I definitely see exactly what you describe in your post with my Series 60 Detroit. My oil pressure gauge regularly shows different readings in regards to different engine temperatures.

Re: Temporary Viscosity Loss [Re: Koop] #5421240 05/04/20 10:06 PM
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As the oil heats up is gets thinner.


2015 F150 2.7
2018 F350 6.2
Re: Temporary Viscosity Loss [Re: Koop] #5421606 05/05/20 12:06 PM
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Is this a debate between % viscosity loss between high temp and high shear? Both can be temporary and permanent. Temporary is self-explanatory (vis thins with temp, vis thins with stretching of VII additive in journal bearings).

Permanent shear down can be due to high temp volatility evaporation, shear breaking down the VII additive. Does the fact these users see return to normal temp & pressure mean both viscosity loss types are all temporary?


Elastohydrodynamic Lubrication makes the world go 'round!
2017 Ram 2500 - PUP 0W-40, Fram XG
2011 Chev Traverse - PUP 5W-30, Fram XG
2005 Chev Kodiak C5500 - PUP 10W-30, Fram XG
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