LaCrosse heater malfunction

[tommybuoy]

My 2008 lacrosse heater malfunctions. Heat will drift out of the vents with the fan on low but on high it blows cold. Thermostat is working properly and coolant temperature is at *215°, the AC works fine. What is the most likely culprit? Mechanics in the shop where I work are baffled.



*Will double check this number but the mechanic says is in the proper range.

 

[Smith1000]

I would first check to make sure the coolant level is not low and top it off if low. Next I would check the heater hose temps with my hands when the vehicle is warmed up. With the heat temp set high, are both hoses hot, indicating the coolant is flowing to and from the heater core. If one is cool, there would be a lack of circulation through the heater core.

 

[BuickGirlFromMars]

My 2008 lacrosse heater malfunctions. Heat will drift out of the vents with the fan on low but on high it blows cold. Thermostat is working properly and coolant temperature is at *215°, the AC works fine. What is the most likely culprit? Mechanics in the shop where I work are baffled.



*Will double check this number but the mechanic says is in the proper range.

Heater core blockage. common on these cars. Also, there is a chance the HVAC needs calibration but i owuld try flushing your heater core

 

[tommybuoy]

Heater core blockage. common on these cars. Also, there is a chance the HVAC needs calibration but i owuld try flushing your heater core

OK, I didn't suspect the heater core because both hoses going to and from the core are hot, however I guess the flow could be inadequate. I'll try flushing. Would there be any advantage to trying the calibration first? If that works it would save me a messy time, I appreciate the reply.

 

[BuickGirlFromMars]

OK, I didn't suspect the heater core because both hoses going to and from the core are hot, however I guess the flow could be inadequate. I'll try flushing. Would there be any advantage to trying the calibration first? If that works it would save me a messy time, I appreciate the reply.

No idea how to do it without a scan tool(I had a scan tool)

 

[tommybuoy]

No idea how to do it without a scan tool(I had a scan tool)

👍🏼

 

[richardnewton]

Are the temperature regulation dial/actuator door working properly?

Any air in the coolant- try bleeding again.

If you have a dirty cabin airfilter that would restrict flow but I don't think it should change the heat. I suppose some critters could have blocked up some of the airducting so worth a quick look.

 

[tommybuoy]

Are the temperature regulation dial/actuator door working properly?

Any air in the coolant- try bleeding again.

If you have a dirty cabin airfilter that would restrict flow but I don't think it should change the heat. I suppose some critters could have blocked up some of the airducting so worth a quick look.

The climate control unit seems to respond as it should. I'm not sure if all the actuator doors open when they should, but the vent air does respond to selecting buttons. As mentioned previously, warm air does drift out the vents when the fan is on low but turns cool when fan speed is increased--making me suspicious that a door somewhere doesn't move properly.

I'll flush the core and recheck for air in coolant when I'm able to get back on it...thx!

 

[oldcarowner]

If your car is equipped with auto climate control you can re-calibrate all the actuator doors in the dash. To do this 1. Turn the ignition off. 2. remove the HVAC fuse for ten seconds then reinstall. 3. Start the car and let it run for at least 40 seconds with out touching any of the controls.
This is the non scan tool process for my '08 Lacrosse.

 

[tommybuoy]

If your car is equipped with auto climate control you can re-calibrate all the actuator doors in the dash. To do this 1. Turn the ignition off. 2. remove the HVAC fuse for ten seconds then reinstall. 3. Start the car and let it run for at least 40 seconds with out touching any of the controls.
This is the non scan tool process for my '08 Lacrosse.

thx for the knowledge! The core flush worked magic but I had been looking around for this process and will do it just to optimize the system.

 

[tommybuoy]

No idea how to do it without a scan tool(I had a scan tool)

Well I finally got the time to do a heater core flush (actually, flushed the block and radiator also) and it did solve the 'blowing cool air' problem I had been having. Also swapped out the Dextron antifreeze for universal type, and replaced the thermostat while the hoses were off. I very much appreciate the input from this forum!

 

[BuickGirlFromMars]

Well I finally got the time to do a heater core flush (actually, flushed the block and radiator also) and it did solve the 'blowing cool air' problem I had been having. Also swapped out the Dextron antifreeze for universal type, and replaced the thermostat while the hoses were off. I very much appreciate the input from this forum!

The universal (Yellow?) stuff may be fundamentally similar to dexcool (Dextron isnt a thing, but its common to say that so dont feel bad)

The flush, regardless of coolant, was probably long overdo. What did the stuff coming out look like?

 

[tommybuoy]

thx, yes, silly Dextron malaprop. The stuff coming out looked rusty red, but fairly benign. I was fortuitous enough to purchase this nugget from the original owner (53,000mi.), living in a retirement community--seems to be well serviced over the years.✌️

 

[G-781955]

Well I finally got the time to do a heater core flush (actually, flushed the block and radiator also) and it did solve the 'blowing cool air' problem I had been having. Also swapped out the Dextron antifreeze for universal type, and replaced the thermostat while the hoses were off. I very much appreciate the input from this forum!

11/18/25....same car same problem...I will try the flush first...