Did you measure the radiator or the hoses close to the engine? I assume the engine was running (as it should be).

If there is only a 5 degree drop across the radiator you have a big problem. Did the radiator have a bunch of colder spots in it? If so, it needs to come out.

Even if you don't have a fan running there should be more than 5 degrees of temperature drop across an open radiator.

We are brothers and sisters doing time on the planet for better or worse. I'll take the better, if you don't mind.
- Stu Harmon