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.
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
Performance will still be worse and wear higher than a warm engine. But there’s no reason you can’t let it warm up on the way. Growing up in Canada it was always body rust not the engine that ultimately did the cars in anyways.
They also advance the timing when cold which increases emissions. I forgot to mention that as well.
> And multi viscosity oils ensure lubrication even when cold.
Improved, still not ideal.
For some reason that doesn’t sound so crazy for Germany though. I’m not sure why.
I didn't say illegal, I said bad.
1. Emissions, catalytic converters and such will not reach full operating temp, so it dumps a lot more emissions than when it's up to operating temp. Diesels were even worse in this regard cause the particulate filter plugs up when idling and then needs to trigger fuel wasting regen cycles.
2. Engine wear/damage. Oil pressures usually don't come up enough to properly lubricate components on the engine while cold idling for long periods of time. (Like, after the rpm's settle back down) This adds unnecessary wear. Should really only run an engine long enough to bring up initial oil pressure and then take it easy in it until it's up to full operating temp. (This is because parts expand at different rates, so pushing a cold engine hard will oftentimes blow seals)