Engine overheating

You might need to clean out your radiator fins so more air can pass through and flush the water cooling system to allow more water flow.

I already cleaned the radiator fins and combed them straight two months ago.

collapsed hose,, stuck thermostat,, clogged heater core, cooling fan in front of radiator not working.try back flushing the hole system. blown head gasket.

Flush the cooling system. If the antifreeze is old, the radiator may be clogged.
Does the engine overheat quickly? Or can you drive for awhile before it over heats?
It's possible your thermostat is stuck closed if it over heats quickly.

When was the thermostat last changed out. It could have failed in partially closed position.

It usually overheats when going up hill. Never had a problem last year in the eastern US but the problem started in May going and coming from the rally in North Carolina. The hill does not have to be very big. Can be long sloping.

What make of vehicle? Diesel or gas? How old is it? What does the engine oil look like? It is black or milky? Do you get white smoke when you're going up hill?

Your best bet is to go to a good shop and have them test the cooling system. They can do a pressure check on the cooling system and check the radiator cap. A bad radiator cap can cause overheating.

Radiators get clogged with rust and casting sand and won't flow enough coolant. If the thermostat sticks open the coolant doesn't stay in the radiator long enough to cool. Hoses can collapse and not flow coolant. Electric thermostats that control the fans can go out. There's a dozen possibilities.

For several years it seemed like I would not be able to solve my overheating problem. I went through the usual suspects (new thermostat, fan clutch, hoses..etc) still had the problem.

Sometimes it would overheat and other times it wouldn't under the same conditions.

It turned out the new fan clutch I had installed went bad. Since it was a new one, I didn't think to check it. Apparently, it was engaging sometimes but eventually failed completely. I found a heavy duty aftermarket unit and haven't had a heating problem since.

I also added a product from Royal Purple. It's called "Wetter Water". You can get it at most auto supply locations or online. As advertised it kept my engine temp at nearly 20 degrees lower than when I didn't use it. It really works... I've used it in three different vehicles.

If your radiator has never been professionally flushed, that would be the first thing that I would do (as mentioned already).

I doubt your's has an electric fan, but (as also has been mentioned) if it does it would be a prime candidate.

The fact that it heats up going up hills indicates that the cooling system just isn't up to par. A loaded vehicle going up a hill in warmer weather is the test for all cooling systems. That is about the only condition that makes the cooling fan come on in our Sprinter unless we are in really hot weather.

Diesel engines tend to heat up more than gas ones. If the hill is long and "sloping" it might increase by 20 degrees or so but not into red. Downshifting helps anyway on long, steep hills for all engines. I had a V10 which overheated on long hills.Certainly, a well maintained cooling system helps a lot. In my experience all/all engines heat up on long hills and even though people say NO, it happens. My 5 series BMW oil temp gauge(no water temp on them) goes up on the long and steep Cocquihalla highway to Kamloops BC.