I used the search function but didnt find any info. 2009 RX 350 V6, no heat from vents unless RPMS are up.

I know the heater core is not plugged as I removed the hoses and used low pressure air to verify flow. I have bled the cooling system and still one heater hose is hot and the other is not. I have worked on cars for 40+ yrs but this one has me stumped. Im open to any and all suggestions. Thank you in advance

ADDED INFO: So i took it around the block and tried to bleed it again, got no air just coolant. BOTH hoses at t he heater core are hot now, Sound like the bend door actuator?

 

Do you still have no heat until the engine revs go up?

 

https://www.clublexus.com/forums/rx-...t-problem.html
https://www.clublexus.com/forums/rx-...-cold-air.html

 

How old is the thermostat? If it's been replaced, is it OEM?

 

Thermostat is factory original afaik. I can change it, since I have a new one with gasket on the work bench. The new one has the bleed hole 180*.

 

I'd swap it out if its the original t-stat......I'd also get a gallon of Zerex asian red as well.....

 

Will do. I am using the Asian red coolant. Won’t get to it til Friday, will report back. Thank you.

 

I have the exact same issue with my 2007 RX350, no heat from the vents at idle, I have bled the system numerous times, and I flushed out the system which was very clean already,if I rev the engine just a little bit I get very Hot air from the vents, it's not a clogged heater core, not a blend door or actuator, it's something under the hood
I have noticed that in park my idle seems low (600)RPM, it's so low that my Oil light flickers,if I barely press on the gas pedal the Oil light stops flickering and I get heat, maybe a dirty throttle plate and or IAC motor?Can a low idle affect the water pump to not circulate the coolant fast enough therefore not letting the heater get hot?,, I have never had this issue before and I have owned quite a few different Vehicles, I even pressure tested the system and it holds 15 psi and No leaks,a new Radiator Cap didn't help either, I don't want to start throwing New parts at it but I am at a loss what to do next

 

While I can't guarantee this is the fix, if you have it, swap it, it's due anyways.

It's possible but I doubt it, a warm engine idles between 600-800 depending on where you are, 600 is low but I haven't heard of it giving idling issues, 500 and under and we got issues. WP is dependent on RPM for both belt and chain models. I believe with electronic throttle body there is no more IAC like it was in my old Highlander but your TB is worth cleaning and so is the MAF (with proper MAF cleaner).

As I asked OP, how old is your tstat? OEM? Is the jiggle valve in the in 12 o'clock position?

 

I have only had the vehicle for a little over a year now, so I'm not sure about the age of the thermostat, but it must be opening up fully because it's not overheated and if I push the gas pedal down it gets very hot, but 5 minutes later at idle it blows cold air instead of heat, could it be a faulty or aging thermostat?
In the past on other vehicles I've replaced the thermostat because no matter if I hold down on the gas pedal it would still be cold and I knew that the thermostat was stuck closed, but this time I'm really stumped 🤔 also I did clean the MAF sensor with the appropriate spray

 

What do the heater hoses feel like at temp? What I notice is it takes awhile to get the engine to temp, even left in a heated garage.

 

+1
I would check if hoses to/from heater radiator are hot when engine is warmed up

 

When the vehicle is at curb idle and at operating temperature I have cold air coming out of the vents, and one heater hose is hot, the other heater hose is cold,if I rev the engine I get heat from vents and Both heater core hoses are equally Hot, I pressure tested the Cooling system at 15 psi and it holds pressure, don't see any coolant leaks, I'm going to replace the 2 foot overflow tank hose that runs from the overflow tank to the radiator and put a small clamp on each end because when I pressure tested the Cooling system it did not include the overflow tank, maybe I will get lucky and it's not a hard or expensive repair to replace the overflow hose

 

both hoses should be hot if the heater is on. there could be air in the heater radiator ("idle engine" can't push the coolant through)
PS: heater radiator hoses:

 

I agree, somehow air is getting into the Cooling system, I have bled the system several times, I'm going to do a more extensive pressure test, taking off anything obstructing the radiator, the cover underneath the car, and replacing the overflow tank hose, hopefully I will see something the next time, I'm preying it's not a Head gasket issue, I have never had a vehicle with a blown head gasket and I hope that's not the case