Originally Posted by fredk
Now this is what can go wrong, the radiator can become clogged, it will get cold spots in it that can be found with your hand,
Wow. I know you mean well, but that is really, really dangerous advice. I think what you probably mean is that you can hold your hand OVER the radiator from the front and feel that it is cold, but I could very easily see someone taking your advice literally and touching the radiator, which can seriously burn you (especially if the car is overheating). Even worse, someone might try to touch the radiator from the inside of the engine bay while the electric fans are not running, and have the fans turn on while their hand is in there.
A more appropriate solution would be to use a laser thermometer to detect for hot/cold spots.
As for the original overheating problem...
If you are overheating while climbing a hill, there are a few places to look to narrow your problem down.
Does it overheat at stoplights? When you are going up a hill, are you talking about hills on the highway, or do you typically loose speed as you go up them?
There are two things off the top of my head that I can think of to test to find your problem.
First, you can remove the thermostat temporarily. This will let you know if the Tstat is sticking closed, or if it there is another problem. Don't leave it out though.
The second thing I would check is the temperature of the front of the radiator when the car is overheating. Compare it to the temperature of the upper and lower hoses. Do this with a laser thermometer. I can't remember them being expensive when I got mine.
These will give you an idea if the problem is in the flow of coolant or the effectiveness of the radiator.