Are you sure the sending unit and the gauge match each other?
Oil gets thinner at high temperatures, so the lower pressure is normal. 1/2 bar sounds a bit kind of low, i don`t know the factory specs though.
As long as the oil pressure lamp does not start flickering at idle when the engine is hot, I think you are on the safe side. You can measure the oil pressure with a mechanical gauge, that should give you a precise readout. What you can also try is to wait till the oil is hot and then try to reduce the engine speed from idling and see when you reach the threshold for the oil lamp to turn on. You can do this if you switch to gear and slowly release the clutch while pressing the brake pedal. If you can`t make the lamp turn on without killing the engine, you are good. If the lamp starts flickering right away the engine speed drops, you have a problem.
If you want higher pressure at idle one possibility is to use oils that are designed for staying thicker at high temperatures. I use 10w-60 oil in old air cooled motorcyle engines that operate at higher temperatures and have high oil clearances, especially when they are worn.
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