Hello, I have a curious issue that I cannot seem to find the answer to on the forums.

I turned on the heater in my 2004 MCS R53 for my girlfriend the other day and she started to complain that there was no hot air on her side. I thought it was weird because my side did have hot air. Now I would not have an issue if this case was the reverse because I am always hot, but she needs it.

I have tried closing my vents and only opening hers with the blower at full blast but I still get the same result no matter what I try. Even the defrost vents on the passenger blow cold air and the driver side blows lukewarm air.

I do not know if it is related but another issue is my coolant expansion tank bubbles through the cap sometimes. I have changed the cap but it only minimized the bubbling for a while and did not fix the fault.

I have seen a few posts about the thermostat and matrix causing issues. Should I start by looking at those components first?

Thanks in advance for the help.

 

Does it blow cold air when the car is still? I think the first thing I would try and check is the integrity of the ducting to the vent from the blower motor, like maybe it's got a hole in it and that's why cold air is getting in.

 

It blows cold at all times. For the first 30 seconds or so when the car is warm and I turn the dial to 1 or 2 lukewarm air will blow but after that the driver side goes a little warmer and the passenger side goes cold. Both sides blow at about the same speed on both sides.

 

I would check to see where the coolant level is and make sure it is circulating. Open the bleeder on the top radiator hose.

 

After I adjusted the coolant level and opened the bleeder valve like Rubidon suggested it put heat out on both sides for a few minutes then I messed with the blower dial position to find that the floor was blowing cold on both sides but the top vents would intermittently blow hot is I moved the position dial around.

I think the issue is simpler than I thought and it is just a combination of coolant level and the heat control unit being faulty. I may just pick another one up at the local wrecking yard and see if it fixes it. I thought about getting the auto control unit but then I researched what retrofitting it would take and it is more complicated that I am willing to do. Manual unit it is!

Thank you for the advice!

 

I replaced my water pump last saturday and I am still removing air from my system. I drive 100 miles a day to and from work. It might take a while to get it all out.

 

I would check the waterpump or see if you have a leak somewhere, to be warm under throttle then cool, shows air in the system.

 

I'd wait on replacing the heater control, as failures of that part are rare.

I'd suggest you properly drain and replace your coolant as follows:

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Coolant Replace/Topup:
​R53 coolant capacity is 6.0 L (6.3 qts) with the tank filled to MAX.
​
The following is from BMW Tech. Information System,
1982-2004, v6.3.1.23B, and addresses the Series R53, engine W/11 Cooper S.

Elevate the vehicle safely on jack stands.
Place tarp or plastic sheet under vehicle.
Carry out work on the cooling system after cool down.

1. Remove cap on expansion tank.
2. Remove the under body protection panel.
3. Disconnect the lower radiator hose, drain and catch the old coolant.
4. Crack upper plastic bleeder screw to facilitate draining.
5. When it stops flowing, reconnect the hose.
6. Loosen LOWER vent plug (10mm bolt) under thermostat housing.
7. You already loosened the UPPER vent plug in radiator hose.
8. Leave BOTH plugs loose so system vents during filling.
9. Slowly pour fresh coolant into expansion tank, watching vent screws.
10. When coolant emerges from vent screws (no bubbles), tighten them.
11. Fill expansion tank until coolant stays at the MAX line without dropping.
12. Place the heater control on HIGH and fan on LOW
13. Start the engine and allow to run at idle, slowly adding coolant if the level drops.
14. Continue idling until thermostat opens,​ cracking the TOP bleeder screw until air no longer escapes, then close it.
15. Make sure coolant stays at the MAX line without dropping.
16. If it drops, slowly add until it stays at MAX level.
17. Take car for a short drive, re-check when cool, and top off (to MAX line) if necessary.