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DIY: Flushing the E9x Heater Core (Caution Required!)
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03-31-2024, 02:31 AM | #1 |
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DIY: Flushing the E9x Heater Core (Caution Required!)
Have you found your heater growing cold, first on one side of the car and then on the other? As long as the heater core isn’t damaged or leaking, it can be flushed. BUT… BE CAREFUL! Many YouTubers recommend pressurizing the core with a garden hose or compressed air as the first step. That could easily burst the fragile aluminum core (especially if weakened by corrosion) or blow one of the rubber o-ring seals inside the dash.
If that happens, allow me to refer you to the DIY from hell… E90 Heater Core DIY. This DIY heater core replacement is incredibly well documented, but the work is difficult and takes days - or thousands of dollars to have this done by a dealer or mechanic. Last edited by GSB; 11-13-2024 at 06:20 PM.. |
03-31-2024, 02:32 AM | #2 |
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Important to Know:
For most BMW E9x models and options, coolant is circulating full-time through the heater core, while the blend doors/flaps inside the car direct hot or cold air into the cabin.
A gentler and more calculated approach to flushing sediment is especially important in this engine, because of the possibility of oil contamination in the coolant. The notoriously flimsy Oil Fiter Housing Gasket separates engine oil from coolant, both of which are pressurized in the engine. When that gasket fails (and it will), oil can leak into the cooling system, perhaps very slowly at first. When oil reacts with coolant, it forms gelatinous blobs of sludge that collect everywhere in the system. That sludge may be relatively colorless at first, and not easily detected, but it is highly corrosive to ALL of the plastic and rubber parts in the cooling system. It also blocks passages and is exceedingly difficult to remove. I discovered that radiator flush products will not budge it. The only thing that worked successfully, was filling the cooling system with a 50/50 mix of SuperClean degreaser and distilled water, then running the car up to operating temp before draining and repeating the process several times. Gobs of sludge came out each time. I've heard mechanics recommending dishwasher detergent tablets as an alternative to degreaser. Note that it is wise to replace all of the coolant after flushing a blocked core because contaminants may be circulating throughout the system. If oil sludge is found in the cooling system, it would be necessary to thoroughly flush the entire cooling system with degreaser first and replace any plastic parts, rubber seals or hoses affected by oil contamination. I found plastic connections so corroded that they just crumbled and fell apart, even turning into a brown, putty-like paste when rubbed between my fingers. Always monitor the health of your oil filter housing gaskets and replace them preemptively to avoid expensive repairs! The potential for oil in the coolant is highly relevant to the heater core flush procedure below. Several reputable mechanics recommend this method as the best procedure to treat any blocked heater core because it works first on oil/grease deposits (which bind the sediments in the core), then on corrosion/scale deposits. Only then, should the loose material be gently blasted out with controlled pressure. It worked wonders for my car and saved me a fortune. Last edited by GSB; 11-13-2024 at 06:52 PM.. |
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03-31-2024, 02:33 AM | #3 |
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Accessing the Heater Core:
Last edited by GSB; 11-13-2024 at 06:56 PM.. |
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johnnyorange66.00 |
03-31-2024, 02:36 AM | #4 |
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Preparing the Flush Procedure:
Last edited by GSB; 11-13-2024 at 08:36 PM.. |
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johnnyorange66.00 |
03-31-2024, 02:38 AM | #5 |
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Flushing Steps:
Last edited by GSB; 11-20-2024 at 02:49 AM.. |
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johnnyorange66.00 leif2033.50 |
03-31-2024, 02:41 AM | #6 |
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Replacing the Coolant and Bleeding the System:
Last edited by GSB; 11-14-2024 at 03:45 AM.. |
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johnnyorange66.00 leif2033.50 |
04-16-2024, 05:43 PM | #8 | |
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You're welcome. I hope the flush goes well for you! |
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06-20-2024, 01:42 PM | #9 |
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This is great. I am finding a little challenge while attempting this DIY. On my 2010 320i LCI, there’s a plastic ring under the metal clamp on the upper hose on the firewall of which I am not sure on how to remove.
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06-25-2024, 01:38 AM | #10 | |
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Mr Mohlake0.00 |
08-01-2024, 04:15 AM | #11 |
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Thank you for the response. I’m not referring to this one you just shared. I’ll try get a picture of the one that I am referring to. It’s basically on the top hose which has the metal fastener. So it sits under the metal fastener and it doesn’t have any kind of screw on it or a place to loosen it.
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08-05-2024, 11:45 PM | #12 | |
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11-11-2024, 09:19 AM | #13 |
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GSB
On page 1, do the red and blue arrows refer to the hot and cold lines? As far as I am aware, the hot line is actually from the bottom of the heat exchanger (the one you put the blue arrow for).
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Reverend_Wrong18.00 |
11-12-2024, 01:13 AM | #14 | |
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Your "hot/cold" diagram is actually slightly inaccurate. The entire length of pipe 23, returns HOT coolant, both from the heater core and from the expansion tank, to the thermostat. Pipe 18 is on the "cold" side of the cooling system. But you are correct, flow direction is IN at the bottom of the heater core, and OUT at the top of the heater core. Last edited by GSB; 11-12-2024 at 03:18 AM.. |
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11-12-2024, 03:12 AM | #15 |
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Here's a more accurate coolant-temp plus flow-direction diagram for the N54 manual-shift engine. The basic N52 coolant flow is the same. Note that electrical operation of the pump and thermostat will determine the temperature of pipes #1, #3 and #7, depicted in purple...
Last edited by GSB; 11-12-2024 at 04:58 PM.. |
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11-12-2024, 12:43 PM | #16 |
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Thanks OP!
I just wanted to drop a quick note to say this method of clearing the heater core worked great for me but I did do a few things differently.
I did buy an amazon fountain/aquarium pump and found that 5/8 OD vinyl tubing fit perfectly in the ID of the heater core hoses and sealed perfectly with a few wraps of masking tape on the OD of the vinyl hose. 1/2" barbed hose fittings on the pump were perfect for the vinyl tube. My pump came with three different size barbed hose fitting and the smallest was 1/2". One thing I also did differently was zip tie a funnel to the wire handle of the bucket I used to submerge the pump. I put a harbor freight disposable paper/mesh paint filter inside the funnel and always placed the vinyl tube with the water exiting the heater core into the funnel/filter. This way you catch all the particulates coming out and can monitor your process as you catch less and less. Depending on how fast I was running the pump, it did look like the pump was pulling some of the sandy particulate I had flushed out and recirculating it into the heater core again so the paint filter funnel system eliminated that risk and gave me a way to see when the particulate seemed to be clearing up. I used CLR instead of vinegar so my process was: 1. Water on low pressure back and forth for maybe ten minutes 2. 50/50 water/degreaser back and forth for ten minutes 3. CLR back and forth for two hours 4. Water back and forth for ten minutes 5. Coolant back and forth for five minutes 6. Reassemble, refill and enjoy the warm heater! Again, thanks OP for the process! I hope my additions make things easier for people doing this in the future. |
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leif2033.50 |
11-12-2024, 02:57 PM | #17 | |
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Last edited by GSB; 11-12-2024 at 03:03 PM.. |
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11-13-2024, 08:54 AM | #18 |
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Thanks for the additional information GSB and sepling!
I hope to do this on the weekend. Info about the fish pump would be helpful - what GPH, variable speed, etc?
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11-13-2024, 05:50 PM | #19 | |
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11-17-2024, 01:28 PM | #20 | |
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11-17-2024, 11:47 PM | #21 | |
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Did you connect a garden hose nozzle and gradually increase the pressure until it was running fully open? When the core is truly clear, it should be able support the full flow of a garden hose (within reason... don't over-pressurize). It took a higher pressure than the pump could provide to blast the heavy sediment out of my core. Pressurize the top of the core first before reversing the flow from the bottom. Last edited by GSB; 11-17-2024 at 11:59 PM.. |
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11-18-2024, 10:20 AM | #22 | |
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I might speed up the process and repeat. Given i've already done it once, I don't think I need to run vinegar again for 2 hours. Maybe CLR for an hour. How much should I open the hose? I do have a regulator at the barb so i can carefully control the flow there.
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