Sorry I can't Wiki oil as it has to be more than 3 letters
Since fitting a pressure gauge I now know that my oil is at 80 when cold then as it warms up it ticks over at 40 but as it gets hotter it drops to 30 on tick over and even 25
so would that be the type of oil or would it be the engine? The oil pump is new but the engine is not.
No it's called hot oil.
every and any oil will get thinner as it gets hotter.
this is a good thing as your engine will be able to pump the thinner oil much faster cooling the hot surfaces and coating them with fresh cool oil
the oil temperature will reflect your coolant temp, so if that isn't working right the oil will get too hot and too thin
Mine starts at 60 psi when cold at tickover then drops to just under 20 psi when warmed up.
an oil cooler will keep the oil slightly below the coolant temp and it will remain more viscous because of that, more viscous means more psi at lower engine speeds where damage is done
I don't know what normal is on a diesel
Mine is a petrol engine.
I just wanted to inform you that it's normal for oil pressure to drop when it gets hot.
if it was too low and likely to cause engine damage the oil light would come on when the low pressure oil switch was triggered.