I apologize if this has been asked before but I’ve searched and searched and I’m still coming up empty. I have a 2010 ES350 and at idle, only cold air blows thru the vents even when the climate control temp is set to HI. Once the engine reaches 1500-2000 RPM the heat is on as it should be. Not fun in stop and go traffic in the winter. The engine temp is dead center of the gauge and doesn’t fluctuate, I’ve recently flushed the radiator with the proper fluid, and have no issues with fluid levels. My first thought was a blend door issue but I’m leaning more towards a water flow problem. I don’t think it’s the thermostat since the engine temp is consistent, possibly an air bubble in the heater core? I’m open to any and all suggestions and I truly appreciate this forum. It’s been a great resource. Thank you all.

 

Check those coolant levels again. Did you use the correct coolant type? You may have a bubble in the cooling system


Water pump could also be going south.

 

Correct fluid type yes, I flushed the system using the over filled funnel and line from the valve on top of the engine until there was a constant flow of fluid with no bubbles present. I thought about the water pump but the engine temp doesn’t fluctuate at all. I drive 30 minutes one way to work and it’s 90% highway speed so I would have thought there would be some change in engine temperature if it was the pump. It’s possible, the symptoms just don’t make sense to me. I appreciate your input, any other thought are welcome.

 

At this point I suspect blend door or heater core blockage

 

Is there are heater valve inline with coolant hoses somewhere, one that opens up to allow hot coolant into the heater core? Some BMW's have these and heater doesn't work if that valve doesn't open.

 

Have coolant system flushed. Residue in heater core probably restricting coolant flow if it takes awhile for heater to kick in.

 

The heater core is looking more and more likely, if the hot air didn’t stop when the RPM’s drop I would think blend door. I’ll probably tear it down so I can at least see if the blend door is functioning properly.

 

I’m confident in the flush I did, and debris in the core could be the culprit, it’s just weird that the hot air is dependent on the RPM’s, I like to start with the least expensive option first and work my way through. Thanks for the input.

 

Not that I’m aware of but I am not an expert, I’ll have to look into it for the Lexus. Thanks for the suggestion.

 

My experience is telling me that you have air bubbles in the system, or not enough coolant inside.

While you filled up the radiator, did you open the valve between the banks?
Did you have any of those problems before you flushed the system?

 

As near as I can remember it started towards the end of last winter, just all of a sudden it started blowing cold air, unless the rpm’s were above 1500.
During the flush I had the valve open and ran fluid thru with the engine running until there was a constant circulation of fluid with no air bubbles present, closed the valve, made sure the fluid was topped off and still have the issue.
I’ve been checking the fluid levels periodically and so far no loss. It does have 180k miles on it and no major issues, I change the oils every 5k and drive it.
Thanks for the input,

 

Did you ever change the water pump?

 

Well, I still believe it's a water flow issue. Low coolant doesn't always trigger high temp on gauge. Water pump issue would most likely show on gauge. Let us know the cure when you find it!

 

Yeah, I still think the core is empty and it fills up when high flow.

The car should be parked on a hill (the engine up) and to let it run 10-15 minutes, also it should be revved constanly. I that way it will fill the heater core.
Also, I am surprised why it is not pulling the coolant from the expansion tank.Maybe you should check the hose, it may be clogged or kinked.