As it got cold here in the last couple of months I noticed a weird issue. I have my climate control system set on auto at about 73* but I noticed that at times it would get cold inside the car after it has already warmed up. After some investigating I determined that when the car is moving everthing seems to work fine. Warm air is coming out of the vents and the temperature is stable. But when the car stops (at a light for example) cold air starts coming out of the vents. I had my hand by a vent and I felt the air go from warm to cold as I came to a stop at an intersection. Is that weird or what? Anybody have an idea what is causing this?

 

do you have any type of defrost mode on?

I drove around all winter last year with the mode on defrost and the arrow pointing down at the footwells. Found out later that anytime the defrost symbol is activated, the AC gets turned on. Now that I have it off defrost mode, my mpg is lower by 1L/100km

 

same here but when i set it on 75 it stays warm

 

Dude I have the same exact issue. 2007 IS250. I can put mine on 85 heat and as long as I'm driving its hot hot but if I stop at a light its like a/c cold. One the engine is completely warmed up its less noticeable but still happens some. I have even gone to the point of if my rpm is above 1000 its fine. Somebody has to know what this is. I'm worried something is going out.

 

I don't know if the Lexus cooling system is anything like the BMW that I just had. But that is a symptom of a cooling system that hasn't been bled properly on a BMW. Did you have any part of your cooling system worked on recently?

 

Nothing besides a brake job and oil changes done on the car in the past 10 months. The air bag light came on last winter and the dealer replaced some kind of wiring connector buried in the dash but I did not notice this issue last winter.

 

Sounds like the same issue here. I did some more investigating. When I'm stopped at a light and cold air is coming out of the vents, I put the car in neutral and rev the engine above 1000 RPM and warm air starts blowing. As soon as RPMs drop below 1000 air gets cold again.

Does anybody know what is causing this? I'm out of warranty so I would prefer not to take the car to the dealer as to avoid having to take out a second mortgate on my house.

 

Just a thermostat Not a Big deal, its not properly Regulating the temp of the motor it might be stuck slightly open

 

Mine did the same thing. Check your coolant level. I added fluid to it and its been fine every since

 

Low coolant level is not normal....... Leak somewhere.....

 

So all three of us have a leak somewhere? Lol. I doubt it. And besides I checked for leaks. And I'm sure MY coolant does get a lil low from time to time when I drive on the autobahn and hit 130MPH every now and then. After all coolant does contain water. lol. To the OP before you start buying thermostats and all this other crap. Check your coolant level. If the heater core is not getting enough coolant it will have the exact symptoms you described. No heat at idle. But when you are driving or revving it heats up. I mean which would you want to buy, a thermostat or a lil bit of coolant?
Could be. OP check for leaks too. Never hurts to look around the engine bay every now and then.

 

Looks like coolant is low. Of course the manual recommends the Toyota brand coolant. What kind/brand do people use for these cars?

 

go with the toyota brand coolant. Its lifetime, so you won't be replacing it anytime soon; and its bad to be mixing different brands of coolant.

Also, its like $20...thats not expensive at all

 

Make sure that the DUAL setting isn't on.

 

Good point, I have a Toyota dealership less than a mile from my house. It's actually $22 + tax.

No, that's not it.