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Cold Air Blows With Heater On Only At A Stop?!?!

21 posts in this topic

I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

Sounds like you might have a gas lock in the heater system, its the highest point in the cooling circuit and when you are idling the pump pressure is at its lowest. How is the fluid level in the coolant reservior?

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i have the same problem on my 96, after research i found out that its a firmware bug. thats what they said about second generation of LS.

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

Sounds like you might have a gas lock in the heater system, its the highest point in the cooling circuit and when you are idling the pump pressure is at its lowest. How is the fluid level in the coolant reservior?

Fluid level is at the top / full level. I've been monitoring it. The only thought I have is that there is a "bubble" somewhere in the system. Typically, does the system need to be purged?

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Are you saying that your temperature gauge goes to max and then returns back to normal operating range once you start driving again..?

I would check your thermostat first. Your engine can he hot while your thermostat will not open to allow flow into your heater core causing it to blow cooler air..

With Temperatures as cold as they are right now 0 degrees and below make sure your coolant is good for those temps as it can freeze and stick your thermostat...

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When you say "Temp is at Max and it will go away after driving again after a few minutes" are you refering to the climate control setting or your temp gauge? If you're getting normal heat when driving as you describe and no heat when idling, I would check your thermostat and test the coolant mix as scott has mentioned. If you've got old coolant and didn't use distilled water when last mixed, you might have deposit buildup partially blocking your thermostat or elsewhere in the system, including your heater core and pump. An air pocket is also a possibility.

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My SO's 01 LS does the same thing. Only thing different is that when the transmission is put into P, it blows warm again. This just started so we haven't diagnosed the problem yet.

I posed the qestion on the forum just now. Should have done a search first and found this thread. Sorry.

Rod

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

The OAT, Outside Air Temperature sensor, is located behind the front bumper just in front of the A/C condensor/radiator "stack". while stopped or moving slowly in heavy traffic it will often be heated via radiant heat from the condnesor radiator and that will sometimes result in coolish airflow from the system. Worse yet, it will sometimes premature "trigger" the climate control's automatic switch from heating mode, primarily footwell outflow, into cooling mode, footwell/dash combined outflow.

Brrrr....!!

Later models, mostly those that also use the OAT sensor for OAT indication to the driver, use a bit of digital signal processing so the HVAC system does not react to short term (false, temporary) temperature excursions.

I moved my '92's OAT sensor into the right front bumper area, well away from radiant effects of the condensor/radiator.

If you truly have the temperature setting at MAX, fully at MAX, then ignore all of the above and focus on a vapor lock in the coolant system.

With the temperature setting at MAX heat or MAX cool all sensor inputs are ignored.

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I just found this post. I too have a 96 LS400 with the same cold air blowing issue and wondered if the original poster fixed their problem - was it an vapor lock or sensor issue. I'm going to test tomorrow by setting my temp to MAX. I think I've done that in the past though, so I may be looking at a vapor lock.

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I just found this post. I too have a 96 LS400 with the same cold air blowing issue and wondered if the original poster fixed their problem - was it an vapor lock or sensor issue. I'm going to test tomorrow by setting my temp to MAX. I think I've done that in the past though, so I may be looking at a vapor lock.

There's a much more recently active thread which suggests checking the heater control valve for a stuck halfway open condition. That's what I'm checking on my 96 next, once I get time (and the New England cold subsides just a bit... btw, no way that sensor placement is playing a role when its 10F outside pre-windchill).

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i'd start by purging the air out of the cooling system. if problem persists, most likely thermostat and THEN heater valve.

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

I have a 1990 LS400 that developed the same problem - baffled me for months. It turned out to be a defective radiator.

These are aluminum radiators and have extremely small passages that are easily clogged if you inadvertently use or top off

with the wrong (i.e. non-Toyota) coolant. Some of these passages had become clogged in my radiator and it had to be replaced.

A new radiator solved the problem and is has never recurred.

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

I have a 1990 LS400 that developed the same problem - baffled me for months. It turned out to be a defective radiator.

These are aluminum radiators and have extremely small passages that are easily clogged if you inadvertently use or top off

with the wrong (i.e. non-Toyota) coolant. Some of these passages had become clogged in my radiator and it had to be replaced.

A new radiator solved the problem and is has never recurred.

I have exactly this same heater hot/cold issue with my '97 LS400. Thanks for the suggestions -- I'll check things out and let you know what I find.

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I have an intermittent problem with my 93 LS400. The heat works great but occassionaly when I stop at a light or in traffic, cold air blows out the heater. Temp is at Max and it will go away after driving again after a few minutes. Anyone else run into this? Ideas?? Thanks

I have a 1990 LS400 that developed the same problem - baffled me for months. It turned out to be a defective radiator.

These are aluminum radiators and have extremely small passages that are easily clogged if you inadvertently use or top off

with the wrong (i.e. non-Toyota) coolant. Some of these passages had become clogged in my radiator and it had to be replaced.

A new radiator solved the problem and is has never recurred.

I have exactly this same heater hot/cold issue with my '97 LS400. Thanks for the suggestions -- I'll check things out and let you know what I find.

Here is the answer, most likely for all Lexus owners. I have a 1994 SC400. No heat. I found a web posting at http://en.allexperts.com/q/Lexus-Repair-818/f_4590148.htm

Follow their directions. This fixed my heater. I think there is a fundamental flaw in the Lexus design. When the fluid level gets low you get a gas pocket that lives in the heater core. This keeps the fluid from flowing through the heater core. I loosened the 17 mm bolt at the top of the thermostat and ran the car at 2500 rpm. At the same time, have the coolant cap off and top off the coolant over and over until the coolant level is finally full. You will get heat after this. Retighten the 17 mm bolt, secure the coolant cap and be happy!

If this works, please pass it on. This will save a lot of Lexus owners a lot of grief and money. It took a total of five minutes to fix!! Yeah internet!!!!

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Vandal, good suggestion.

Except for removing the water inlet bolt, that's basically the instructions for purging air from the cooling system. There should be instructions on how to do it posted on a label on the reservoir. I added to it and came up with this:

1) Remove the tank cap

2) Set heater temp on high (85)

3) Let engine warm up to normal operating temp (to open the thermostat)

4) Rev engine between 2000 and 2500 RPM for 5 minutes (at some point you may see some fluid "blurp" (technical term) out as the air escapes)

5) Turn off engine and let engine cool

6) Add fluid to the tank as coolant is drawn back into radiator (don't let tank get empty)

7) When engine is totally cool, add fluid to full level

8) Replace cap

which I posted previously in this thread:

http://us.lexusownersclub.com/forums/index...showtopic=53882

As for the inlet bolt, I'm told the 98-00 models don't have them.

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I initially posted to this topic in Jan '09 with my '97 LS400 not blowing heat at idle.

I tried to test the issue by first putting the heat to MAX but that didn't change anything.

I then tried the simple approach to topping off, but it didn't need much and that didn't fix it.

Last weekend i finally got around to topping off the correct way as described in this topic and on top of the reservoir, but I don't know where that 17mm bolt is and if it is necessary to fixing the issue. Anyway, that didn't fix it either, but did create one additional question. The directions on the reservoir say something like 'fill up to the bottom of the neck' but that is almost an inch higher than the FILL line on the side of the tank. I stopped at the FILL line, should I have gone higher? If not, should I move on to the thermostat, then the heater valve as described in another post or does anyone else have another suggestions before i get into that??

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It is a basic air bubble in the heater core.

You have to fill the coolant level up , with the heater on max heat and rev to 2500 rpm , then recap the coolant res.

It solved my issue after draining it.

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It is a basic air bubble in the heater core.

You have to fill the coolant level up , with the heater on max heat and rev to 2500 rpm , then recap the coolant res.

It solved my issue after draining it.

My issue is that I did run the car at 2500 RPM for 5 with the heat on MAX and topped it off to the fill line and still have the issue. Are you recommending I try it again? I thought for sure it would fix the issue given everyone else's success, but no dice for me. I wonder if draining it as you did would help.

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I have a 95 LS400 ... and this winter I started having the same problem everyone else here is talking about ..... my problem only started to happen to me after the car had been sitting for most of the winter in the garage not being started at all or driven .....

I thought I should fire it up cuz it had been sitting so long ..... so when I did, the heater did not work, as per what everyone else has said here .... exactly the same thing. At idle, it starts to blow cold, even though the engine is at normal operating temp. Then as I start moving and come up to about 35 mph, the heater starts to give me hot air ....

in my case, my coolant reservoir is perhaps too full .... I have been thinking about lowering the fluid level just about an inch ..... I also got a new fluid reservoir coolant cap, thinking perhaps the old cap (original and never changed before) is not working correctly?

it is interesting to see that other owners have also been having the same issue .....

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try it again , as well as a good highway strech for 30 minutes.

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Problem finally sovled. The car was in the shop to have the starter replaced so I had them flush the cooling system (among other things) and that got the air pocket out so I now have heat when idling. I was unable to resolve it using the method that others have suggested with running the motor with that cap off.

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