Re:Pedestrian fatally crushed between two parked cars after ...
by joecool1029 on Friday December 13, 2019 @01:59AM
(#21779667)
This is mostly correct observation with an incorrect conclusion. Oil pressures under load will be higher until oil temps come up. This is due to decreasing viscosity that improves the fuel flow. It still remains though that slower moving pump moves less oil (the volume doesn't change with temperature, just how quickly it falls back to the pan) and less oil even with a higher pressure may not provide adequate lubrication.
The other major issue that specifically effects cold idling is that the ECM is going to increase the amount of fuel dumped into each cylinder, past what gets completely burned. This leads to problem called 'quench' that leaves gasoline behind on the walls of the cylinder after combustion. This will mix with the oil on these areas and actually dissolve it over time.
Anyways, don't take it just from me. No manufacturer specifies over 30 seconds of idle time for their vehicles: https://info.ornl.gov/sites/publications/files/Pub61263.pdf
I haven't seen this in practice. In fact, I see the opposite. My 2003 350z has an oil pressure gauge, and when it's idling while cold (say, < 40 degrees F), the pressure is actually higher than it is when cruising on the highway once it's warmed up.
I attribute this to the oil being "thicker" when cold.
On a really cold start, the pressure goes well beyond 60 PSI until the RPMs taper back down from around 1500 to the normal cold idle of ~1000, at which time it drops a bit.