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.

 

maybe the water pump is broken? Before you start the 4Runner in the morning (or when the engine is cool) take the radiator cap off then start the engine. Look into the radiator and you should be able to see the coolant moving, if its not then I would guess it a water pump or maybe some blockage.

 

bypass the heatercore. Youll know where it is you will see two rubber hoses about 6 inches apart. Disconnect the hoses (not at the core you may damage the ends) and connect them to eachother. Let it run if it doesnt over heat your core is bad.

 

x2 use a 90 connecter the same size as the heater core tubes, t connect the hoses. to replace the core you must pull the dash apart can leave it like till you really want heat.

I used to do this on my nova in the summer to stop the heat from killing me never shut off!