Well, prototype complete and working well. I think it would be pretty easy to make two versions of this.
One would use one temp sensor. Depending on the weather, you could set the temp you would like the spray to turn on. Of course this is needed because while a 100 degree IC isn't bad in the middle of the summer, that's really bad in the winter. You need a way to tell the sensor how hot is hot.
The second version can use two sensors to determine the ambient temp and then you would set the difference. For instance, if you want the spray to come on when the IC is 30 degrees higher than ambient, you'd make that adjustment and then it will take care of the rest, regardless of outside temp. 30 out, spray at 60. 100 out, spray at 130.
Here's a few pics. Not pretty, but I need to get a real board made now that I know it works.
Here is the two sensor model. At this point, IC and ambient are the same temps, so the spray is off (light off).
And here, when I apply heat to the IC sensor, the spray comes on (light on)
I'll let everyone know when I get a 'pretty' version together and of course if it really works on a turbo w/ IC car.