Question, is it a electrical sender unit or mechanical?
The reason I'm asking the electrical sender may be reading wrong since you said it hasn't boiled over, 240 is pretty warm.
I had one that was off by almost 30 degrees (autometer), compared to a mechanical unit.
Running straight water will make it run quite a bit cooler, also using some of that water wetter stuff will help. Redline makes some $10 a bottle.
Using straight water and water wetter should drop it around 20 degrees and also do like dparker suggested - fully enclose the raditor with a fitted shroud.
You just might need a bigger radiator with that intercooler in front of it those things emit off alot of heat.
Goodluck and let us know what helps.
Cp