fountain 10 meter oil temp please help
 

i have a 1986 fountain 10 meter 454 with around the 500 hp range 61.9 hours on motors problem is oil temp is getting way to high and only under load above 4500 rpm or wot oil temp 260 + sb motor
slow back down or come to idle temp will come back down . if i stay under 3000 rpm it will run 230 240 all day. motors have remote filters and i do not have a circulation pump i have the crossover tube no thermostats on water water temp here in indiana is still cold so i dont have much water temp some where around 100 to 130 i have read that the remote filters have t stats in them ??? if so where at where can i buy them please help thanks
things i have done
backed flushed coolers
new oil filters with merc full syn oil

Borrow a non - contact temp gun , my oil gauge reads that also , but after hitting with the non- contact temp gun ,
my actual temps were about 25 - 30 degrees lower .Point the gun right at the same location the sender is installed .