Hemi oil weight, is it really that sensitive?

[The Critic]

That doesn't make sense to me. I would believe in gear at a stop light would be lower than idling in park since the engine RPM would be lower.

Yeah, those figures are impossible.

 

[Plawan]

That doesn't make sense to me. I would believe in gear at a stop light would be lower than idling in park since the engine RPM would be lower.

Yeah, those figures are impossible.

I look at it every time I drive the truck and it’s always higher in gear hot than in park hot.

 

[twX]

Not sure if oil pressure is correlated to HT/HS? I thought it was more aligned with kinematic viscosity.

Oil pressure correlates much better to HTHS than to kinematic viscosity. Here's a graph showing the correlation. It was taken from here. The original data is from a BITOG post somewhere.

The largest oil pressure drops are going to be across things like bearings, cam journals, and other restrictions where shear rates are going to be pretty high. As far as I can tell, kinematic viscosity isn't as relevant as HTHS to any aspect of engine lubrication.

 

[OVERKILL]

Yeah, those figures are impossible.

Yep, at the same oil temperature.

 

[OVERKILL]

Oil pressure correlates much better to HTHS than to kinematic viscosity. Here's a graph showing the correlation. It was taken from here. The original data is from a BITOG post somewhere.

The largest oil pressure drops are going to be across things like bearings, cam journals, and other restrictions where shear rates are going to be pretty high. As far as I can tell, kinematic viscosity isn't as relevant as HTHS to any aspect of engine lubrication.

View attachment 206444

Now that's a great graph!

 

[BornSlippy]

I wonder if this was an early attempt by Chrysler, going back to when they were owned by Mercedes.

https://360.lubrizol.com/2024/Understanding-0W-20

In the past, OEMs often specified multiple engine oil specifications and/or viscosity grades for use in vehicles. It was not uncommon for a new vehicle to leave the factory with a 0W-20 engine oil, only to have higher viscosity grades added during routine service for the remainder of the vehicle’s life. However, Europe is introducing “In-Use Verification” rules, which require that the vehicle’s CO2 and emissions performance must comply for the whole vehicle life. This means that OEMs have now transitioned to specifying a single engine oil specification and viscosity grade for servicing. This means that any new vehicles leaving the factory with a 0W-20 engine oil are much more likely to continue using 0W-20 engine oils for life.

 

[4WD]

My Pentastar has digital oil pressure read-out and it’s the same with 0W20 or 5W30 …