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Rear Radiator Clogged, How To Unclog?

999 Views 13 Replies 6 Participants Last post by  BillG
I have a 2007 Sienna XLE. The heat runs in the front seat but in the rear, it blows out only cold/cool air. After troubleshooting it over the phone with a mechanic friend, it seems that the rear radiator (maybe "radiator" is not the correct term but part that the radiator fluid flows into in the rear behind the passenger side back panel) is clogged. He said that the only way to unclog it was to either remove it completely or hook up the hose pipe to it and flush it out (which could make a mess). I called the Auto Parts Store and the person I spoke to said that it could be flushed from the engine. So, I am looking for advice on what options might exist to flush out the clog. (Trying to find the method that will avoid radiator fluid flowing all over the back seat). Also, I checked the servo motor in the back and that seems to be working okay. My mechanic friend thinks it is clogged because of the two pipes running into it the top one gets warm but the bottom one stays cool.
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It could be clogged or it could be "clogged" (with air). The only way it could actually be clogged is if you (or someone else) put something (i.e. stop leak) into the cooling system or you have another problem where something got into the cooling system (i.e. trans fluid or oil) and congealed in the rear heater core. The system is a closed system. What typically happens isn't a clog, but a bubble of air will get stuck in the rear heater core. The only fix for that is to get the air out by bleeding the system and hope you don't have a leak somewhere.
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I believe the '07 has a 1-year cooling system which a was a transition from the '06 to the '08. So, you may have the radiator with the filler back near the firewall or you may have the one with the fill neck on the radiator itself. If your coolant is low enough to starve the rear heater core, it's probably too low to find the leak with a pressure tester. To fill it, you get yourself a spill-proof funnel and fill it with the proper 50/50 mix of coolant and then run the car with all heaters on, blowers on full and let it come up to temp. Every so often, you squeeze the fat radiator hose (unless it's too hot to touch). As it draws in coolant from the funnel, you have to keep topping it off. It'll probably take 20-30 minutes of running to get most of the air out. Once the system is full, make sure the overflow tank is at the correct "full" level because, as it cools off, it should draw coolant from the overflow tank. After that, you will probably see the wetness/dripping of coolant. There are a few cases where you won't, though. It can leak in the front, between the condenser and the radiator. It can leak into the transmission (which can be fatal) and it can leak into the combustion chamber (from a definitely fatal head gasket leak). I know the '04-'06 can leak into the valley, but I don't know if that affects the '07. The heater cores can also leak, although, that's uncommon. The rear one leaking should be visible from under the van. The front one would cause the front passenger carpet to get wet. If you can't spot the leak with a visual check, you'll need to do the pressure test to verify if it happened to just be low. You can loose a drop or two every so often, and that can add up over the years to make it low. Still good to verify though.
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