1998 4runner overheating
I have a 1998 4runner V6 4wd. Last weekend, it overheated, so I replaced the thermostat and the coolant. I ran around town all week, with no issues and no over heating. Last night, trying to take a longer trip, the engine overheated, and when I pulled over, there was steam coming from underneath the passneger side in what looked like some metal tubes for the rear blower. I flushed out the radiator, and refilled it wiht coolant and let it run for about 20 minutes in the driveway. Everything seemed ok, so I went inside and coming back out, it was venting again out the side on the passneger area again. What could be causing this, and what is the fix? Is this a heater core issue and how can i test this? POR is this indicative of something like just weak lines or blocked lines that need to be replaced? thank you for any help you can give me on this matter.