Ran UV dye through the cooling system. Trying to figure out exactly where the small leak is coming from. I am preparing for a radiator replacement, but want to perform some diagnostic work before spending that money. Plan on renting a pressure tester tomorrow and bringing the cooling system up to pressure while investigating with a uv leak dye light. Any other tips or advice? Oh, I plan on testing the radiator cap as well if I can.

 

Year, mileage, specific engine type (4.0 OHV or 4.0 SOHC) always helps.
The dye you used requires a light to view it, no? If so try looking tonight before you do the pressure test as dye may have oozed out the leak enough to see.
Keep things quiet when you pressurize the system as you may get lucky and hear it hiss.
Is there any "frosty" looking residue? That'd be dried coolant.

Get some clean cardboard (fridge box) and put it under the vehicle to help locate the source of the leak.

 

Its a 1997 ford ranger, 132,000 miles, and it is a 4.0 liter OHV.
The dye that I use is UV ray activated and is a bright green hue under UV light. Night time helped a little. I was lucky enough to be able to rent a loaner coolant pressure tester this morning and utilize it while it was still quiet out. I heard the stream of a leak of coolant as I brought it up to 16psi (1.1bar). Come to find out I just needed to tighten 2 of my replacement hose clamps from when I replaced the upper and lower radiator hoses from when I winterized it.

 

Always nice when it's something simple, and even better when the fix is free.