My 500hp carb motor in my new fountain. Is running just over 260deg on gauge. Temp sender is in block just above filter pad. I back flushed cooler (haven’t visually looked silent choice exhaust in way). Changed oil thermostat for shots and giggles. Drops when idling usually. Any ideas. Gonna change gauge because I’m updating dash anyway. But

Check with infrared gun to verify temp. What is water temperature? Do you run a t-stat?

When is it running over 260? Cruise? WOT? How long to get to 260+?

Is this freshened engine? What oil pump?what oil pressure you running at cruise and wide open? Suspect your relief valve in the pump.

What's your timing set at?

Sorry been dealing with fam stuff.
Engine completely stock
-water temp 140-150. Thermostated
-timing 34 deg full advance with wire grounded
​​​​​​—pretty much always in 260-270 oil my temp range on gauge slowly climbs as it warms up and then always above 260 on gauge
oil filter adapter on back of engine very hot
-oil psi 50-70 depending on rpm . 80-85 cold

seems sensor is in block just above filter pad on block

waiting for new gauge and sensor.

It would be worth checking that the oil cooler is plumbed correctly, the water should go in the same end that the oil comes OUT, and the water should come out the same side the oil goes IN. That countercurrent flow is necessary for proper heat transfer. And, even if you backflushed, you might need to pull the cooler to visually inspect that all the tubes are open and able to conduct flow.

Interesting, I need to check mine, could be why I run a bit hot as well.

Not at all disagreeing with the Dr that water and oil should flow against one another. I've run it both ways with negligible noticeable differences. Definitely worth looking at. Next, what size cooler do you have? Is this a new issue?