OM366LA Oil Pressure

Joe. Possibly, Although 3000m isnt considered too high here.

I went to that height a few weeks ago but overcthe course of a day and the pressure remained normal. My tempreture on thiscoccasion also remained normal as it it was a very gradual ascent.

I think it has to be related to tempreture not altitude and this would tie in with the pressure returning to normal after idling the engine for 10 minutes at the top and the temp dropping back down.

There has to be a connection there.

I have some passes of over near 5000m meters coming up soon so I will watch it closely.

Interestingly even at 2500 m you can feel a difference in engine performance.

Starting from cold takes a lot longer andcthe exhaust smoke is more visible.

Absolutely engine temperature effects oil pressure! Higher RPM's also effect pressure. All oil will thin out once the engine gets up to normal operating temperature...that's what it's supposed to do. I would be more concerned with low pressure. It being a diesel and driving it on a long uphill grade will always run alittle warmer then normal but from what you have stated I don't think there is anything wrong. Stick with the 15w40...10w30 is too thin for that motor and it's from the "old" design so I don't recommend synthetics either. Good luck!
Certain motor oils are designed to be thinner (less viscous) when cold and more viscous (thicker) when hot. For instance, multi-grade or multi-viscosity motor oils show a low viscosity at low temperatures and high viscosity at high temperatures.

The idea is to provide thin oil when the motor is started and to provide an oil of the right thickness at the operating temperature.

These multi-grade or multi-viscosity oils can be identified by designations such as 10-30W.

These numbers refer to specifications developed by the Society of Automotive Engineers (SAE).

The "10W" in this example corresponds to the lower oil viscosity when the engine is cold and not running. The "30" refers to the higher oil viscosity when the engine is hot and running normally.