Heater

[raymond123]

I turned on my heater this morning and got nothing but cold air , outside is 18 degree and inside about the same . Do I have a broken thermostat ? I drive a 96 Ls 400 -never had this problem before .

Ray

[raymond123]

I turned on my heater this morning and got nothing but cold air , outside is 18 degree and inside about the same . Do I have a broken thermostat ? I drive a 96 Ls 400 -never had this problem before .

Ray

[4howard]

welcome to the club. i have never been able to resolve this. spent $2k at the dealer, worked for a bit, then zip. Had the coolant changed, system bled, burped, dont even remember what else. still cold except when traveling at consistent highway speeds. wish i had the answer...

[dpellet]

There are lots of us with late models having the same troubles. I have finally after months think I resolved the issue.

In all while I tried to fix this I wound up changing: Radiator, Thermostat (twice, finally went with OEM), water pump(failed). The last thing I did was replace the o-ring in the coolant reservoir and tighten it down. This spot would regularly weep and you could see it get wet around the top.

Once the system was sealed and the OEM thermostat installed I burped it and have had no troubles with it for about 6 weeks now, just happens that the last 6 weeks have been pretty cold and heat has not been an issue at idle.

Hope this helps!

[RDM]

My car does this too, and I've found a slight leak around the front coolant 'bridge' somewhere, just haven't attacked it yet. It seems the cooling system on these cars is designed to divert flow from the heater core in case of low coolant level, to avoid engine overheating. When my tank is full there's always heat, but as soon as it gets to a low enough point there's only heat when driving above 3k rpm. The temperature gauge never moves though during these times, confirming that the coolant isn't getting any hotter even when down a little. An air leak would also do the same thing as coolant leaking out means air is coming in, causing an air pocket somewhere that moves through the system when really pumping, but stays put at idle.

Check for leaks and refill the system to the proper level, that's the first and most effective step.

[curiousB]

My car does this too, and I've found a slight leak around the front coolant 'bridge' somewhere, just haven't attacked it yet. It seems the cooling system on these cars is designed to divert flow from the heater core in case of low coolant level, to avoid engine overheating. When my tank is full there's always heat, but as soon as it gets to a low enough point there's only heat when driving above 3k rpm. The temperature guage never moves though during these times, confirming that the coolant isn't getting any hotter even when down a little. An air leak would also do the same thing as coolant leaking out means air is coming in, causing an air pocket somewhere that moves through the system when really pumping, but stays put at idle.

Check for leaks and refill the system to the proper level, that's the first and most effective step.

A stuck open thermostat would greatly delay engine warm up on cold days. It should show up on temp guage in dash too. If engine shows cold for extended warm up time then go ahead a get a new thermostat. If the engine seems to warm up but the heater is cold then fluid flow into heater core is either blocked or slowed. That could be corrosion plugging the heater core or the diverter valve just head of the heater core is stuck and not routing fluid through the heater core. Could also be an air lock there is a procedure to filling coolant to avoid such air locks.

[90LS400Lexus]

Not sure.... I have heard of alot of heating woes on the 1995-97 models. Sorry about your misfortune in this cold air blast.

Thats one thing good I can say about my 1991.... my gosh the heat gets so hot on maximum setting. It dont take long either.

[RDM]

A stuck open thermostat would greatly delay engine warm up on cold days. It should show up on temp guage in dash too. If engine shows cold for extended warm up time then go ahead a get a new thermostat. If the engine seems to warm up but the heater is cold then fluid flow into heater core is either blocked or slowed. That could be corrosion plugging the heater core or the diverter valve just head of the heater core is stuck and not routing fluid through the heater core. Could also be an air lock there is a procedure to filling coolant to avoid such air locks.

True, but my car heats up fine and the gauge is always accurate. And as I said, at speed there's plenty of heat, it's only at idle that it goes cold. A thermostat would not have that effect.

[raymond123]

Not sure.... I have heard of alot of heating woes on the 1995-97 models. Sorry about your misfortune in this cold air blast.

Thats one thing good I can say about my 1991.... my gosh the heat gets so hot on maximum setting. It dont take long either.

[curiousB]

A stuck open thermostat would greatly delay engine warm up on cold days. It should show up on temp guage in dash too. If engine shows cold for extended warm up time then go ahead a get a new thermostat. If the engine seems to warm up but the heater is cold then fluid flow into heater core is either blocked or slowed. That could be corrosion plugging the heater core or the diverter valve just head of the heater core is stuck and not routing fluid through the heater core. Could also be an air lock there is a procedure to filling coolant to avoid such air locks.

True, but my car heats up fine and the gauge is always accurate. And as I said, at speed there's plenty of heat, it's only at idle that it goes cold. A thermostat would not have that effect.

Another thought. Someone complained a while back of cold air and found a diverter plate/door inside the air box had disconnected from the actuator and was unable to move to the position required for heat. Unfortunately it’s buried in a tough spot behind the dash so maybe a little ugly to diagnose.

[curiousB]

Another thought. Someone complained a while back of cold air and found a diverter plate/door inside the air box had disconnected from the actuator and was unable to move to the position required for heat. Unfortunately it’s buried in a tough spot behind the dash so maybe a little ugly to diagnose.

Another thought^2. Recall seeing someone saying before water pump impellers can get so corroded that they don't pump fluid well so at low RPMs (i.e. idle) coolant flow is low and heater core doesn't get enough flow. At higher RPMs flow returns and heat magically reappears. I think it was a post by billydpowell if memory serves.