which oil pump (sealed power or melling)

Hi Timo,

so it seems that your engine does not need the hv pump because the pressure is ok.

Where do you measure the oil temp? did you back up this values with another gauge? Electric / mechanical gauges?

As far as i know a modern oil can handle the 270° temperature. I´d use a good synthetic one.

Try another thermostat, 160° for example. Maybe you can lower your overall operating temperature of the engine - and your oil temp.

Good luck!

Michael