Passat Heater Not Working: 2000 1.9PD Fix

I have a radiator that's not heating up, and I thought it was probably the heating element.
I then tried to verschandeln it with a radiator cleaner. I drove with the cleaner in the system for a day, and then oil started leaking out through the expansion tank.

Okay, so I replaced the oil cooler and added another cleaning agent, but the oil is no longer getting into the water, but it's still not heating up. I then checked the temperature control valve actuator, and it seems to be working. I also disconnected the linkage and manually set it to the "hot" position, but the heating still doesn't work.

I then measured the temperature of the radiator hoses leading to the heater core using an infrared thermometer. I got approximately 75°C on both hoses, but the outlet temperature at the vents was not even lukewarm, but rather cold.

Okay, so I disconnected the small hose on the expansion tank. Only water comes out when I hold it down for a bit, but I tried the same thing on another Passat and it's the same. The water pump was replaced only 5000 km ago.

The only thing that seems strange to me is that when I open the expansion tank and press on the radiator hoses, I don't hear any gurgling. However, I did fill the cooling system under vacuum.

I know that the radiator coolers tend to accumulate scale, but if that's the case, shouldn't the hoses be at different temperatures?

Hello,

Can't you disconnect the hoses to the heat exchanger from the engine compartment and blow or flush the heat exchanger to check the flow?

Best regards,

Replaced the heating cooler today, and the heating is working again.