Restoring my 220 D - Page 2 - Mercedes-Benz Forum

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post #11 of 23 (permalink) Old 10-08-2016, 07:10 AM Thread Starter
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Hello,

That line "circled" goes from the water pump, through the firewall, and into the heater core. There are two lines that exit from the heater core near the dual heater control valve on the upper left side of the firewall. From the dual heater control valve, the coolant goes back to the engine.

Best Regards,

Brian
Hmm, so you mean this is the water going to the engine, not the water coming back to the engine? I was a bit confused because I have a book where they explain that the other hose, which goes from the heater core (at least I believe it's the heater core) to the engine block is actually the water going to the heater. So I supposed the one I circled on the picture is the water returning? But the book may be wrong too. Sadly it doesn't say anything about this line.
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post #12 of 23 (permalink) Old 10-08-2016, 07:18 AM
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Originally Posted by Winegarden View Post
Hmm, so you mean this is the water going to the engine, not the water coming back to the engine? I was a bit confused because I have a book where they explain that the other hose, which goes from the heater core (at least I believe it's the heater core) to the engine block is actually the water going to the heater. So I supposed the one I circled on the picture is the water returning? But the book may be wrong too. Sadly it doesn't say anything about this line.

Hello,

My belief is that the circled line is a supply line to the heater core as it comes out of the water pump and goes to the heater core. So this is water going from the engine to the heater core. It's backwards from what you would expect.

Best Regards,

Brian
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post #13 of 23 (permalink) Old 10-08-2016, 07:45 AM Thread Starter
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Originally Posted by reifsnyderb View Post
Hello,

My belief is that the circled line is a supply line to the heater core as it comes out of the water pump and goes to the heater core. So this is water going from the engine to the heater core. It's backwards from what you would expect.

Best Regards,

Brian
Yes, I see what you mean. I think my book may be wrong. Someone else also told me that this is the water going from the engine to the heater core, and not the other way around. I always need to know what is what exactly, because I write down everything and need to know what to actually write! Thanks for your input.
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post #14 of 23 (permalink) Old 10-08-2016, 08:11 AM
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The metal pipe is indeed the return line.

The coolant is supplied from the lower radiator outlet, enters the system through the lower hose housing, flows into the water pump cavity where the impeller (it's not actually a pump as it doesn't compress anything) creates the flow through the coolant passages and exits via the top radiator hose. The thermostat, located in the housing connected to the upper radiator hose, controls the flow by opening or closing.

The heated water is supplied by an outlet from the intake manifold. This is the valve located on the firewall operated by cabling connected to the heater valve controls in the dash (the "sliders"). The water enters the valve through the center formed hose. The position of the valves determines if and how much heated water passes through the heater cores (there are two within the actual heater core unit, driver's and passenger's sides) and exits through the return pipe. Minimal flow, if any, occurs through the return line when the heat valves are in the "off" condition.

The coolant system pressure is created by the expansion of the heated coolant and not the "pump".

Heater core. The line on the LHS of the picture is the return.
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Last edited by Mike D; 10-08-2016 at 09:02 AM.
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post #15 of 23 (permalink) Old 10-08-2016, 04:21 PM Thread Starter
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The metal pipe is indeed the return line.

The coolant is supplied from the lower radiator outlet, enters the system through the lower hose housing, flows into the water pump cavity where the impeller (it's not actually a pump as it doesn't compress anything) creates the flow through the coolant passages and exits via the top radiator hose. The thermostat, located in the housing connected to the upper radiator hose, controls the flow by opening or closing.

The heated water is supplied by an outlet from the intake manifold. This is the valve located on the firewall operated by cabling connected to the heater valve controls in the dash (the "sliders"). The water enters the valve through the center formed hose. The position of the valves determines if and how much heated water passes through the heater cores (there are two within the actual heater core unit, driver's and passenger's sides) and exits through the return pipe. Minimal flow, if any, occurs through the return line when the heat valves are in the "off" condition.

The coolant system pressure is created by the expansion of the heated coolant and not the "pump".

Heater core. The line on the LHS of the picture is the return.
Thanks! I haven't occupied myself a lot with the heater yet, just moved some knobs so far and saw some things opening & closing. When I see it in real together with your message I'll be able to picture how it works and write it down in my "book" before remove it all. :
Sadly my daily car has some problems now, so I have to quickly fix that first… argh.
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post #16 of 23 (permalink) Old 10-08-2016, 10:54 PM
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I concur, the upper single line on the heater core is the inlet. The two lower pipes are the outlets. Inlet is up by the driver side of the firewall, and the dual pipes exit the firewall just above the hump at the midline on the passenger side. DO a citric acid flush after you run a hot soapy solution through the core. This will teach you where and how the heated water flows through and illuminate how the adjustments work. Best to clean the heater core before install, as there is a bunch of gunk that seemed to build up in mine.
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post #17 of 23 (permalink) Old 10-09-2016, 08:41 AM Thread Starter
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I concur, the upper single line on the heater core is the inlet. The two lower pipes are the outlets. Inlet is up by the driver side of the firewall, and the dual pipes exit the firewall just above the hump at the midline on the passenger side. DO a citric acid flush after you run a hot soapy solution through the core. This will teach you where and how the heated water flows through and illuminate how the adjustments work. Best to clean the heater core before install, as there is a bunch of gunk that seemed to build up in mine.
Yes, I'll definitely be doing that! Everything needs to shine, even on the inside.
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post #18 of 23 (permalink) Old 10-10-2016, 07:35 AM Thread Starter
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BTW, what happens with the water that goes back to the engine block? Is it just making "rounds" then, like going to the heater and back, to the heater and back, etc. etc.? Or does it go somewhere else also?
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post #19 of 23 (permalink) Old 10-10-2016, 07:54 AM
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Yes. It mixes with the water being drawn through the lower water inlet, though the coolant passages in the block and exits via the top hose to begin the journey all over again.

With the heater control valves in the closed position the flow is interrupted and it becomes a dead loop. Because of the chances of sediment build up, it is a good practice to have one of the heat selection sliders to be just barely in the heat position to ensure you have at least a partial flow though the heater core.
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post #20 of 23 (permalink) Old 10-10-2016, 03:07 PM Thread Starter
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Yes, that's pretty smart. But I guess sediments would only build up if you never use the heater at all, like if the slider has been on 0/off for years? But It's a great tip anyway.
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