Reposted from another thread:
your pressure gauge is the best indicator you have of the motors warm-up. High pressure is not a good thing, it tells you that the oil is very thick (cold) and resists flowing, not good for the motor...hence why it is believed that cold starts make for 80% of the wear of the motor. Upon warm-up, when the pressure finally reduces, oil becomes more useful as a lubricant. Unfortunately, temperature is the key parameter for lub properties, not pressure. The motor is designed to a specific viscosity, and it just happens that 15W-40 reaches that viscosity right around 200 degrees. Anything much lower or higher, and you get less than the intended lubrication.
On cold mornings, viscosity is so high, the oil won't run through the filter. One of the best longevity moves you can make is discipline to avoid cold starts, plug-in to keep the oil warm for that morning start. I also use and recommend a 5W-xx or 0W-xx oil. It makes a good difference.
The more sustained load you experience, the higher your oil temperature. Some year groups get hotter than others. The LLY has other issues that also make oil temp worse.
Ballpark: if you are driving hard enough to kick on your fan, oil is 240 minimum. If that load is sustained, oil rises above 300 F. That temp is the cause of your gauge pressure drop...decreased viscosity...decreased lubrication...you get the picture.
Unloaded vehicles are not subject to the same. Oil typically runs 20 degrees warmer than water, following a design spec.
