Nick12684

New to the forums and having a heating issue with my '06 RX400h. When the car is stopped/idle and the engine is off (running on the battery/electric motors) it won't blow hot air out of the vents, but it will blow (cooler) air. Starting up from a cold engine to get up to temp and when I'm driving around (engine is running) I have no issue with the heat, but as soon as that engine shuts off and runs off the battery I start to lose heat. I've had it for a year and don't think it has done this until now, but it would make sense that you'll have a loss of heat if the engine isn't running to pump coolant through the heater core. I've checked Advance auto and Autozone to see if my car might have a electric water pump to get the water through the heater core when the engine is off, but it doesn't look like it. I almost always use the floor heat setting, so the maybe it's normal and I'm just now noticing that I only have heat when the engine is running? Seems like kind of a flaw, especially when it's January and you are stuck in traffic or something. Expansion tank is full, but coolant in the radiator is not "topped off" (meaning you don't see any if you take the cap off) and there are no signs of leaks. So I don't know what is going on here and looking for some insight from you guys.
Thanks!
-Nick

Nick12684

So I'll reply to myself, because there is no one else here.
I believe I've solved it. Even though the expansion tank was full, I tried adding to the radiator itself and it took a 1/2 gallon of coolant and I didn't even burp the system. After that, I had no issue with heat when the engine was off and running on battery. I suspect I had enough to cool the engine and just a little left over (ore maybe even not enough) for the heater core so the only time when the heater core saw hot coolant was when it was being forced through it, otherwise it was being used to cool the engine. Addition of coolant directly into the system allowed for it to sit in the heater core for the blower to send the hot air into the cabin, until the engine kicked back on and cycled it through the system to keep (enough) hot water in your heater core.

So if you are having a similar issue, check your coolant levels......you may have air pockets and/or really be down water. A gallon of 50/50 is a whole lot cheaper and easier than spending the time to replace a T-stat or taking it somewhere and wasting (lots of) your money.

alex1372

Had same exact issue with mine and it seems that it's resolved by adding more coolant (1/3 of a gallon in my case)