This could be a couple different issues so we need to start with checking the temp with a laser temperature meter on the hoses to find out if the thermostat is closed when cold and then opens when it heats up.
https://www.2carpros.com/articles/how-to-use-an-infrared-temperature-meter
https://youtu.be/SNRb6pSwYuU
https://www.2carpros.com/articles/replace-heater-core
If the thermostat is not closing then when the engine heats up all the hoses will be the same temp before and after the thermostat.
This will cause it to heat up slowly. However, it will not cause the heater to not perform well.
That sounds like a blend door issue or a heater core issue so we need to check the temp of the heater hoses in the engine bay going into the heater core when the engine is warm and heat is on. They should be pretty close to each other and about the same temp as the rest of the hoses.
If the temperature are different then the heater core is most likely restricted and not heating the air. If they are the same then we need to look at a blend door issue.
Let me know what questions you have. Thanks
Apr 24, 2021 at 2:49 PM
