Question about Engine high temperature

My car is a Daihatsu Storia 1L Manual. Recently I found the temperature meter goes really high after I put more pressure on the gas at up hill road at lower gear such as 2 or 3. Then I found after driving 20-30km doesn't matter what kind of road even motorway, it goes to about 70-75% high of the temperature meter.

I have replaced the thermostat and coolant, it doesn't make any better. When the temperature goes high, I stop my car, found out the radiator is cool on the blade from the front (I can touch it by head), kind of hot on the top. I only can reduce the temperature by turn the air conditions on by using the heat from the engine, so warm air from the car. It can reduce the temperature really fast.

I am wondering apart from thermostat, anything else could cause the temperature problem?

Thanks a lot.

If you have a restricted radiator, either internally or due to debris in the fins, it could cause what you describe. If your water pump is worn and the impeller is not circulating coolant well, it could cause what you describe. Also, if your electric cooling fan is not working properly, it could explain why turning on the A/C seems to help cool things down. Also have your pressure cap tested to make sure it's pressurizing the system properly.

-Rod

If turning on the HEATER works to cool your car down, then yuor problem is cooling. Replace the rad.

If turning on the AC system works to cool your car down, then your problem is cooling fans. When the AC is on, your electric fans both turn on whenever your AC compressor is on. With AC off, run your car until it starts to heat up, or getting ready to overheat and check to see if your electric fan is ON. If not, this is your problem. Then you have to diagnose why the fan isnt working. This is only if you have elec fans on this car.

if the radiator is cold when it is overheating, then you have a flow issue. Could be a plugged radiator, bad/inop waterpump, or air in the system that is causing the t-stat to close. A blown headgasket can cause that.