Best way to drain heater core

[BigDave]

I want to drain my entire cooling system. How can I drain my heater core without having to disconnect the heater core hoses? Can I have the motor not running but the ignition turned on and the heater turned on? Will that open the heater core valve that will allow the heater core to drain along with the rest of the cooling system?

[Slideways]

I'm not sure about the heater core, but there is the plug to drain the block and that should get most of the coolant out of the system.

[Gt4]

If you disconnect the hoses from the recirculating pump under the intake elbow, that should drain heater core pretty much. Make sure to use a floor jack and lift passanger rear side to help coolant get out the heater core.

[BigDave]

If you disconnect the hoses from the recirculating pump under the intake elbow, that should drain heater core pretty much. Make sure to use a floor jack and lift passenger rear side to help coolant get out the heater core.

Our cars don't show a recirculating pump. What does BMW call this item? Do you have a part number in REALOEM? That way I can find it in the schematic.

[BigDave]

I'm not sure about the heater core, but there is the plug to drain the block and that should get most of the coolant out of the system.

Yes, the block drain which drains the Block but not the heater core. I am well acquainted with that. Thanks.

Heater core retains all its coolant when the rest of the system is drained. Because of a valve that by default is CLOSED and only OPENS when you run the heater in the car. That's how a heater works in most cars.

[bmwfnatic]

Our cars don't show a recirculating pump. What does BMW call this item? Do you have a part number in REALOEM? That way I can find it in the schematic.

https://www.realoem.com/bmw/enUS/showparts?id=BL91-EUR---E46-BMW-M3&diagId=64_0890

#2

[Casa de Mesa]

Having removed my motor recently, I'm not sure there any way to *completely* remove all of the coolant from various places in the motor without really getting into the car.

That said, what Gt4 suggested is probably the best approach. You could also use compressed air to help the process. I'd use around 20psi max if you do this. But if you want the best possible chance of removing as much coolant as you can from the heater core, try this.

First disconnect hose #2 (in the link bmwfnatic posted) from the auxiliary water pump, this will drain coolant from the right hand side (when viewed from front of car) of the heater core. Then, separate the quick-disconnect heater core hose from the rear of the motor that connects to the other side/left side of the heater core (part number 5 - here is a visual). You can use compressed air in the end of hose #5 to force the coolant through the heater core and out the end of hose #2 that used to be connected to the auxiliary water pump.

This picture is basically what I just described but the quick disconnect on hose #5 isn't yet disconnected (red arrow).

[tcp]

I want to drain my entire cooling system. How can I drain my heater core without having to disconnect the heater core hoses? Can I have the motor not running but the ignition turned on and the heater turned on? Will that open the heater core valve that will allow the heater core to drain along with the rest of the cooling system?

I turned on the heater, e.g. max temperature and lowest fan speed, with the key in position 2 after draining the block and more coolant came out. I've no idea if it drained the core completely, though.

[George Hill]

Remove the hoses from the firewall connections and blow compressed air in both of the fittings until dry, thats the closest you'll get to emptying it without pulling the heater case.

[Slideways]

When replacing the heater core, does the coolant from the two lines need to be drained?

I'm assuming that a burning smell (not oil) from the heater vents when the dial is turned to red is caused by a small leak in the heater core.

[bigjae46]

Just drain the coolant system, turn on the heater and blow air into the thermostat where the upper rad hose connects. The water pump will help evacuate the coolant. Should blow out the coolant in a few seconds.

When replacing the heater core, does the coolant from the two lines need to be drained?

I'm assuming that a burning smell (not oil) from the heater vents when the dial is turned to red is caused by a small leak in the heater core.

I'd think you'd need to evac the AC and drain the coolant to remove the heater core?

He might be OCD and has a strong desire to get out as much of the old coolant during a coolant fluid change. I can relate.

[Slideways]

Just drain the coolant system, turn on the heater and blow air into the thermostat where the upper rad hose connects. The water pump will help evacuate the coolant. Should blow out the coolant in a few seconds.



I'd think you'd need to evac the AC and drain the coolant to remove the heater core?

He might be OCD and has a strong desire to get out as much of the old coolant during a coolant fluid change. I can relate.

Removal seems pretty simple. This guy doesn't drain anything and just removes the heater core. There appears to be a plastic drain under it and I think this exits above the transmission -

It is the original unit, so I am guessing it has developed a leak which is causing the smell. Turning the dial to blue (fresh air) stops the odor.

[sapote]

I'm assuming that a burning smell (not oil) from the heater vents when the dial is turned to red is caused by a small leak in the heater core.

It should be obvious if you have to top off the coolant often, do you?

[heinzboehmer]

Removal seems pretty simple. This guy doesn't drain anything and just removes the heater core. There appears to be a plastic drain under it and I think this exits above the transmission -

It is the original unit, so I am guessing it has developed a leak which is causing the smell. Turning the dial to blue (fresh air) stops the odor.

Damn I had no idea you could service the heater core without removing the dash. That's good to know.

I'm surprised no coolant spills out when removing the core, siphon effect and all.

Edit: Ah wait the system is closed, so no atmospheric pressure on the other side of those lines. Similar idea to holding your finger on top of a straw and not having the fluid spill out.

[Slideways]

It should be obvious if you have to top off the coolant often, do you?

I checked earlier when the engine was completely cold and the level is a centimeter or two below full. I always thought that the system would lose a small amount due to evaporation, but I guess the heater core has a tiny leak.