Mitsubishi Repair: Overheating, radiator cap, mitsubishi mirage

Question
1993 mitsubishi mirage ES, 1.5L, 4 cylinder automatic. My car keeps overheating. It doesn't over heat while I am driving at speeds of 35 or over. It seems to overheat at idle and while stopped at redlights or stop signs. I have replaced the thermostat and the radiator cap. I have drained the radiator and removed the lower hose from the radiator and ran water through the radiator. Water comes out of the lower hose and out of the radiator drain tube and the opening where I disconnected the lower hose. I do not see any water in the oil (it is not milky or anything). Oil looks normal. Radiator antifreeze looks normal. Replaced hose and filled radiator with 50/50 mix of water and antifreeze. While at idle, the care runs hot. The fan is working properly and the 2nd fan comes on when the air conditioner is turned on. I am lost. After running the vehicle, if I slowly loosen the radiator cap, the water boils over into the overflow resevoir. With the the radiator cap off and the engine idling a little the coolants bubbles out of the radiator cap opening.  Can you please give me an idea of what I should do next? Your help will be greatly appreciated.

Oscar  

Answer
Oscar,
It's possible your radiator is no longer working efficiently.  Remove your radiator fan and your A/C cooling fan from your car (there should only be a couple bolts and eletrical harnesses to remove).  With the fans out, you will be able to inspect your radiator much better.  Check the fins on the radiator and look for any damage.  You may even want to unbolt the radiator at the top and just push it forward so you can look at the front of the radiator.  You cannot see the front  of the radiator from the outside of the car since the A/C condenser is in the way.  There may be a lot of leaves between the condesner and the radiator, preventing your radiator from working properly.

It's also possible your water pump is starting to get weak, and is not moving your coolant around as quickly as it should while your car is idle.  If you have never had your water pump replaced, it would be a wise maintenace item to have replaced.  Water pumps are typically replaced when a timing belt is replaced, so if you have ever had your timing belt replaced, your water pump was most  likely replaced as well.

I had just replaced the radiator in my 1990 Eclipse because it had corroded badly and was not cooling my water efficiently enough while my engine was idling.  You should be able to find an aftermarket radiator for around a hundred bucks.  It should only take a couple hours to replaced as long as you don't have too many overly rusty bolts.
Good luck!