Good afternoon,

I have a 2005 XC70 with about 185K miles. The heater wasn't working, and my mechanic suggested that it might be the heater core. I swapped that out. There are no leaks or anything and both pipes into the heater core are hot once the car warms up. However, the heat does not seem to be as warm as it should be. What is my next stop on the journey? Not sure what to do. Thank you.

Both sides of the heater box have flimsy plastic arms that open and close the blend doors. Those arms are easily broken when replacing the heater core especially if they weren’t “parked” in the position that is out of the way of the heater core removal. Or the arms may have just been dislodged from where they connect to the blend door shafts. It’s worth a look-see.

Like the other folks I’m thinking stuck open thermostat or blender door not working correctly.
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Will I buy another Volvo??? We'll see....

Sounds complicated! Any ideas where I might find information for how to un-stick a stuck blender door? Is there a way to tell if the thermostat is working? I am thinking that I may not have needed to replace the heater core!

Couple of quick checks:
1. Is your engine's temp gauge showing normal operating temperature after the engine is warmed up? Dues it stay there? If not, chances are it’s your thermostat. They are cheap.
2. Try shutting all the other vents leaving just the floor vents open. Does that improve the heat?

I have never attempted to fix a blender door so I will leave that topic to someone else...:)

Matthews Volvo website is an excellent resource for FWD/AWD Volvos.
https://www.matthewsvolvosite.com/

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Will I buy another Volvo??? We'll see....

Robert DIY on YouTube has a recent video on thermostat replacement. He also has info on finding and correcting problems with a Diagnostic code reader. It would be a good idea to have your system read for fault codes rather than replace parts at random. I' wouldn't call the thermostat a random part. Buy the correct Volvo part and be careful when undoing the 2 screws as Robert shows.
Depending where you are he might be able to help you out as he travels far and wide. I think he may still be home in Alberquque at the moment but is I think going to go back up the east coast.

Thank you all. I appreciate all of the help and the quick response, as always.

To verify the thermostat is working, I usually let the engine idle for a few minutes and check the upper radiator hose with an IR thermometer and watch the temp climb.
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Keeping it running is better than buying new

Maybe your thermostat is stuck open?

My 1964 Beetle used to cook my right foot while the left one froze.

If your center dash vent is open to outside air (the air mix vent), it will cool the heated air in the center dash. Other than that, if both dials are set to 84F and the blower is on with the engine temp at normal operating temperature, you should have very warm air. Don't expect to toast marshmallows. The ECC will still mix cool air until the outside temps go below 40F.

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Keeping it running is better than buying new

Thank you Klaus. I don't believe there is an outside air vent on this car (like there was on my old V70). Maybe it's just not cold enough today for the heat to come on. I did crank it up, and warmer air was coming out than before the new heater core.

Thanks again!

Could the blend door's control motor be broken or otherwise defaulted to FULL OPEN?

In extreme scenarios like the those in old Popular Mechanics "car fix" stories, the specter of a stuck open thermostat would always loom. Maybe check your stat's operation.