If it's an older, raw cooled motor, scaling can be a problem, as for my olde Volvo MD17C.
Sometimes, whan scaled, the poor motor has trouble getting the coolant to reach those regions that would be cooled easily when new.
Though I have never used them, some owners recommend the use of de-scalants. make sure the motor is hot before you circulate them, or the thermostat will not let them into the motor coolant jacket.
The last rtesort is to take off the exhaust manifold and de-scale all that you can see.
In my humble opinion, I would not run an older motor that hard... 3100 rpm is pushing it a bit... that's 86% of max.