For past a year and half, I have been chasing this driver's side having no heat (on and off since I have a multiple cars).

Summary to work done
- 185k miles, timing belt and water pump/thermostat done (all lexus parts)
-212k miles, water pump gasket replacement and had genuine lexus thermostat done as well.
-236k miles, all new servos replaced due to some noises from old servos failing. (all genuine parts)
-237k miles, dealership coolant flush
-238k miles, a brand new radiator replaced and coolant flush

Every time I do coolant flush and have the nose up high in the air, I would get some heat back to driver's side but as soon as I put nose down to ground level, it slowly disappear. I put my hands on both of heater hoses by rear engine/firewall and they are hot/same temp. Is it heater core problem? I did notice old radiator was somewhat clogged and never caused any overheating issues. My coolant reservoir was very dirty and had black gritty looking sediments sitting on bottom. I had to clean out the reservoir before I installed it back on.

This is very very frustrating and I can't figure out why I do not have heat on driver's side. Please help me solve this stupid issue.

 

When you say you have no driver's heat, do you get heat on the passenger side? If so then it sounds like a servo issue or more rare the climate controller itself has issues.

If you thermostat is good and you notice that both of your heater hoses going to the heater core are a similar hot temperature, then you should have good coolant flow through your heater core.

 

Propably you have a blocked heater core. If your old radiator and reservoir were dirty, then this is where the residual dirt will be.

 

Its going to be a servo issue if one side gets heat and the other does not. There is only one heater core for both driver and passenger