Heat Only Blowing When Accelerating?cold Air Blowing When Sitting At I

[david1walker]

Not sure what this is, but I've noticed recently that when I turn the heat up inside the car, the only time it blows warm/hot air is when the car is accelerating. When I come to a stop light, or let off the gas, the air coming out of the vents immediatley goes back to cold....even when the temp is turned all the way to 'hot'. What does this sound like??????

[billydpowell]

Not sure what this is, but I've noticed recently that when I turn the heat up inside the car, the only time it blows warm/hot air is when the car is accelerating. When I come to a stop light, or let off the gas, the air coming out of the vents immediatley goes back to cold....even when the temp is turned all the way to 'hot'. What does this sound like??????

This has been covered many many times, do a search or check this link

http://us.lexusownersclub.com/forums/index.php?showtopic=67323

[david1walker]

As always Billy, thanks for the help. For some reason when I did a search, I couldn't find that thread. Thanks! I will have my thermostat checked, as it was replaced in the summer. My guess is that I got a bad one.

[kevin4747]

Search the website for this, same thing has been occurring with my SC400, only I have to deal with the engine overheating as well. Search for 'heater blowing cold air; heater control valve; cooolant; thermostat'- there are many threads as it seems the V8 has a common issue with the entire coolant system. If this is your only issue, hopefully you're just low on coolant or air got into the system, and with the heater core (the heat element of the HVAC system) being at a high point in the loop, it doesn't get hot coolant flowing through, but I can't say for sure the exact way to top off coolant or bleed out air, b/c I'm not a firsthand expert, and I've found about a dozen different opinions on how to work on the coolant system. Hopefully this helps and you could just pay a mechanic an hr of labor to top off fluids correctly without needing new parts. Other than that it seems like there can be issues with the coolant resorvoir (leaking and/or not maintaining pressure), leaks in the radiator or associated plumbing, bad thermostat, or a faulty valve where heated coolant enters the HVAC system. I can tell you if you're determined to top off the coolant level, only take the cap off after engine has cooled, and get the pink Toyota coolant, which seems like it should already be mixed to the proper 50% coolant/50% distilled water solution, and I found a procedure that sounds straightforward to bleed air out where you start the engine,loosen the thermostat (but the forum doesn't show you how to do this) and take the cap off the coolant resorvoir, gas the engine to about 2500rpm, and fill resorvoir with coolant to proper level (though I can't find instructions on what the right level is), and the air will bleed out as you do this for about 3 minutes, stop the engine and when it is cooled top off coolant again, (but I can't find exact instructions- when do you close the thermostat?, and it sounds like there is a gasket in place to seal the thermostat correctly). Sorry if I can't help, but please, someone give us some definitive and detailed advice on how to maintain the coolant- after all isn't the best insurance for a car to keep its fluids topped off?

[AzHotLS]

I found a procedure that sounds straightforward to bleed air out where you start the engine' date='loosen the thermostat[/quote']Loosen the thermostat? What? Not needed and not a good thing to do regardless.

Instructions for bleeding the air are in the link that billy posted.

Another possible, but less likely, problem is the heater control valve is stuck or not opening to let hot water in the heater core.

[steve2006]

I found a procedure that sounds straightforward to bleed air out where you start the engine' date='loosen the thermostat[/quote']Loosen the thermostat? What? Not needed and not a good thing to do regardless.

Instructions for bleeding the air are in the link that billy posted.

Another possible, but less likely, problem is the heater control valve is stuck or not opening to let hot water in the heater core.

Agree don't loosen the thermostat there is a nut you can remove on the housing,also agree on the heater valve easy to check put the heat on full and feel both pipes are hot and see if the thing operates mechanically.

[Zett123]

Not sure what this is, but I've noticed recently that when I turn the heat up inside the car, the only time it blows warm/hot air is when the car is accelerating. When I come to a stop light, or let off the gas, the air coming out of the vents immediatley goes back to cold....even when the temp is turned all the way to 'hot'. What does this sound like??????

Just had the exact same thing happen to my 2001 LS430, it was low coolant level. I topped it off and took care of the problem right away. Problem is, it happened again so I got a leak someplace in the system. It must be a small one because I can smell the anti-freeze but there are no visual signs of it on the ground as of yet. I would look for a leak someplace if you fill it up and then it happens again over a few weeks time. Your fluid is going someplace.

jz

[landar]

Just had the exact same thing happen to my 2001 LS430, it was low coolant level. I topped it off and took care of the problem right away. Problem is, it happened again so I got a leak someplace in the system. It must be a small one because I can smell the anti-freeze but there are no visual signs of it on the ground as of yet. I would look for a leak someplace if you fill it up and then it happens again over a few weeks time. Your fluid is going someplace.

jz

If you still have your under-engine cover installed, take that off carefully, looking for evidence of a leak dripping from above. The cover could prevent you from seeing anything on the ground depending upon the severity of the leak (hopefully, its external to the engine).

[Zett123]

Just had the exact same thing happen to my 2001 LS430, it was low coolant level. I topped it off and took care of the problem right away. Problem is, it happened again so I got a leak someplace in the system. It must be a small one because I can smell the anti-freeze but there are no visual signs of it on the ground as of yet. I would look for a leak someplace if you fill it up and then it happens again over a few weeks time. Your fluid is going someplace.

jz

If you still have your under-engine cover installed, take that off carefully, looking for evidence of a leak dripping from above. The cover could prevent you from seeing anything on the ground depending upon the severity of the leak (hopefully, its external to the engine).

Landar.. Thanks, I forgot that thing was on there. It is 17 degrees out and I will check it when it get into the 30's.

JZ

[JBK642]

I just fixed this problem last week on my '96 LS400. The cold air blowing at low RPM's is caused by air in the line that gets trapped at the high point, which is where the heater control valve is located. When your LS400 is cold, start it and run it for 5-7 minutes at 2500 RPM's... adding coolant as necessary. You should see some air bubbles escaping from the coolant tank. Once you run for 5-7 minutes, shut off vehicle and continue to add coolant to system as it cools (the coolant will be sucked into the engine coolant system for several minutes). You may need to repeat this process once or twice (1 or 2 days apart) to ensure you get all the air out.

[VBdenny]

Classic symptoms for low coolant level. Top off and go. Loosen the thermostat?

[curiousB]

Could be air lock on wax cup side of thermostat. Make sure "jiggle valve" (yes thats what they call it as odd as it sounds) is situated in the highest possible point. Then follow air bleeding instructions as your refill or top up coolant.