Originally Posted By: The Critic
I would recommend doing a complete cooling system rebuild. New hoses, thermostat, water pump and radiator, since the system is over ten years old.
I disagree with replacing the majority of your cooling system without doing a little homework first.
I'd agree that the bottom hose should be replaced since the top one is bulging, cheap enough. Instead of buying the generic hoses from your local auto parts store see if you can find the OEM hoses for cheaper online. Thermostat and water pump should be CAREFULLY inspected (and reused if your Mitsu is low millage). If your Mitsu is higher millage then thermostats are cheap. Maybe your erratic temps are coming from a thermostat that's gone bad. Water pumps can be pricey, so of course inspect for bad bearings, leaks, shredded fins, etc. Check the radiator fins for leaks or rusty spots. After a couple of flushes the water should come out clear. If you're getting chunks then maybe your radiator is too far gone.
Flush the system using WalMart (or other cheap) distilled water. By flush I mean drain, replace hoses, refill with distilled water, drive for 15 min, come home, drain, refill with distilled water, etc. Finally refill with appropriate anti-freeze/coolant.
I'm not suggesting using bad or suspect parts or half-baked anything. But throwing new parts at an undiagnosed problem seems wasteful to me.