So, I commute about 100 miles daily, one way mostly down hill one way mostly uphill. My car runs fine until about 20 mins of driving on the free way. The temperature stays normal until I get it power to speed up or to pass somebody. then it will shoot to the 75% or 80% mark line (2 lines down from red). On the way home it does the same thing going up the hill. Now at first I found a crack in the expansion tank so I melted some nylon plastic over and around the area and it fixed the leak. The cooling system now holds pressure. The problem was still there so I replaced the thermostat. Still the same problem. sprayed out the radiator of bugs, same problem. I've ran the heater and bled the system. same problem. THere is no oil in the coolant and the oil looks perfect, no weird smoke coming from exhaust. I bought htis car 3 months ago from the dealer who did the water pump timing belt etc..

any ideas?

 

Check the coolant reservoir cap.
If the tank itself split, then the cap may need replacing too.

 

The cap looks fine. The dealer replaced it when before they sold it. They also told me they checked everything. I called them up and he suggested that it could be a clogged radiator. I mean this thing is 10 years old and had low miles on it. What I'm thinking happened was that the previous owner let it sit for a while and the coolant / water in the radiator corroded the cooling ducts within. IM going to remove the radiator today and put a garden hose in the top and see if it's doing its job correctly.

 

Lots of overheating issues on forum lately from several US members. (Various models)
I understand that your having very high temperatures over there currently.
Might account for it running a bit over normal?
If the dealer had checked everything they would surely notice a clogged radiator.
You might need a new radiator anyway if it looks corroded and tired.
Was their check prior to your purchase offer or afterwards?

 

Check the Low fan setting.
These cars have problem with the resistor for the low fan going out.

You can check this by taking out the low fan relay in the engine fuse box and shorting out the 12V power and the wire for low fan.