[e90yyc]

2007 328xi – ~400,000 km (250k miles)

Chasing weak heat and a significant driver/passenger temp imbalance.

I’ve flushed/back-flushed the heater core twice:

• Garden hose method
• Transfer pump with TSP + water

Heat output improved, but passenger side is still ~6 °C cooler than driver’s. On very cold days (Canadian winter cold), overall performance still isn’t where it should be. I’d like to properly address it.

Given the labor involved—and the fact I’ll need to evacuate/recharge the A/C—I’m wondering what else makes sense to tackle while I’m in there.

Other context:

1. Evaporator replaced by dealer in 2015 (~200k km). I know these commonly fail. Was the updated part actually revised, or are they still prone to leaking? No signs of leakage currently.
2. A/C compressor is noisy when engaged (groan that changes with RPM). Silent with A/C off. I have a replacement bearing, but not convinced it’s actually the bearing.
3. With recirc on and negative cabin pressure (usually sunroof vented), there’s a noticeable whistle from the HVAC box. Not mirrors. Possible fresh air intake seal issue?

What would you address while the dash is apart?

[kkasson]

Originally Posted by e90yyc

[*]A/C compressor is noisy when engaged (groan that changes with RPM). Silent with A/C off. I have a replacement bearing, but not convinced it’s actually the bearing.

Are you hearing this in the engine bay or through the vents? There's a known problem where you get this slight groaning noise through the vents if the AC system is slightly low on charge. I've used a can of pure R-134a (no additives) and I give mine a tiny bit of gas every couple years to get rid of the noise.

Regarding the heat - have you confirmed the temperature differential between the inlet and outlet hoses? I'd want to be absolutely sure it's the heater core before tearing it all apart.

[KClemente]

I can only comment on the heater core replacement, but if you're clever enough, you can sneak the heater core out without having to touch the evaporator. All I had to do was drop the steering column from its support brace and gently bend the heater core coolant pipes out of the way.

It's not by the book but it saves a ton of time and money

[tlow98]

Have you tried flushing The heater core first? You never know the type of coolant that was used before your ownership. It’s an easy process that has helped many people in your situation.

[GSB]

Originally Posted by e90yyc

2007 328xi – ~400,000 km (250k miles)

Chasing weak heat and a significant driver/passenger temp imbalance.

I’ve flushed/back-flushed the heater core twice:

• Garden hose method
• Transfer pump with TSP + water

Heat output improved, but passenger side is still ~6 °C cooler than driver’s. On very cold days (Canadian winter cold), overall performance still isn’t where it should be. I’d like to properly address it.

Given the labor involved—and the fact I’ll need to evacuate/recharge the A/C—I’m wondering what else makes sense to tackle while I’m in there.

Other context:

1. Evaporator replaced by dealer in 2015 (~200k km). I know these commonly fail. Was the updated part actually revised, or are they still prone to leaking? No signs of leakage currently.
2. A/C compressor is noisy when engaged (groan that changes with RPM). Silent with A/C off. I have a replacement bearing, but not convinced it’s actually the bearing.
3. With recirc on and negative cabin pressure (usually sunroof vented), there’s a noticeable whistle from the HVAC box. Not mirrors. Possible fresh air intake seal issue?

What would you address while the dash is apart?

You'll be taking on a massive job with dash disassembly and reassembly. If you've resigned yourself to tackling this job anyway, you have nothing to lose by attempting a more thorough heater-core flush first, before ripping into the dash. I know that you've tried a flush, but you've only done 2 of 3 vital steps. Your first step was to run TSP, a strong alkali degreaser through the core. Perfect! That will dissolve oils and greasy substances that bind the sludge in the core, but now you need to run a mild acid through the core in both directions to loosen the metallic scale before pressurizing with a garden hose. Circulate vinegar (5-10% strength) through the core overnight, in both directions, before gradually pressurizing the core again. The sequence, the technique, and the direction of pressurization, is important because that scale in the core is heavy, like wet sand, and it takes quite a blast to get it out (but only after properly loosening the scale so you don't burst the core).

I know you've checked in with the following thread, but for reference, I'll post it here for others... DIY: Flushing the E9x Heater Core (Caution Required!)

[fastboatster]

Originally Posted by KClemente

I can only comment on the heater core replacement, but if you're clever enough, you can sneak the heater core out without having to touch the evaporator. All I had to do was drop the steering column from its support brace and gently bend the heater core coolant pipes out of the way.

It's not by the book but it saves a ton of time and money

does that include dash and dash support brace removal? I saw some posts indicating that one of the dash support brace bars gets in a way, and I think these were pre-LCI cars. Is that the case for LCI cars or any e90s at all?

[KClemente]

Originally Posted by fastboatster

does that include dash and dash support brace removal? I saw some posts indicating that one of the dash support brace bars gets in a way, and I think these were pre-LCI cars. Is that the case for LCI cars or any e90s at all?

Here is a picture of when i did mine. I just moved the brace a little out of the way

[e90yyc]

Originally Posted by kkasson

Are you hearing this in the engine bay or through the vents? There's a known problem where you get this slight groaning noise through the vents if the AC system is slightly low on charge. I've used a can of pure R-134a (no additives) and I give mine a tiny bit of gas every couple years to get rid of the noise.

Regarding the heat - have you confirmed the temperature differential between the inlet and outlet hoses? I'd want to be absolutely sure it's the heater core before tearing it all apart.

Regarding the noise: Both. I think the system is a little low on charge, but sadly it is no longer possible to purchase R134a in Canada without a license. (It’s not sold in non-refillable containers anymore either.) Would like to give this a try though. Maybe I can find a can of black market R134a just to see if the system is low. That’s the logical starting point. Wish I could just buy it from a store…

Not a significant temp difference between inlet and outlet. See thermal image below.

Originally Posted by KClemente

I can only comment on the heater core replacement, but if you're clever enough, you can sneak the heater core out without having to touch the evaporator. All I had to do was drop the steering column from its support brace and gently bend the heater core coolant pipes out of the way.

It's not by the book but it saves a ton of time and money

Thank you!! And thanks for the pic! That changes the calculus for me for sure. Not that I particularly want to pull my dash off, but not having to decide if I want to drop an extra $1000+ CAD on AC system parts makes the decision easier.

Originally Posted by tlow98

Have you tried flushing The heater core first? You never know the type of coolant that was used before your ownership. It’s an easy process that has helped many people in your situation.

Twice now, yeah. Might try a third time with CLR, despite it being ill advised.

Originally Posted by GSB

You'll be taking on a massive job with dash disassembly and reassembly. If you've resigned yourself to tackling this job anyway, you have nothing to lose by attempting a more thorough heater-core flush first, before ripping into the dash. I know that you've tried a flush, but you've only done 2 of 3 vital steps. Your first step was to run TCP, a strong alkali degreaser through the core. Perfect! That will dissolve oils and greasy substances that bind the sludge in the core, but now you need to run a mild acid through the core in both directions to loosen the metallic scale before pressurizing with a garden hose. Circulate vinegar (5-10% strength) through the core overnight, in both directions, before gradually pressurizing the core again. The sequence, the technique, and the direction of pressurization, is important because that scale in the core is heavy, like wet sand, and it takes quite a blast to get it out (but only after properly loosening the scale so you don't burst the core).

I know you've checked in with the following thread, but for reference, I'll post it here for others... DIY: Flushing the E9x Heater Core (Caution Required!)

Thanks! Not stoked on the idea of dash removal, but I also am tired of dicking around with flushing. I had been toying with using an acid to flush for the same reasons you describe, though I was thinking CLR. I know it’s not compatible with aluminum, but considering the alternative is dash removal, I can accept the risk.

I wish my flushing setup was better. I generally try to buy stuff of decent quality, but I opted for some chintzy Amazon transfer pump on the basis that I’d just resell it after. It refused to prime despite the head being well within its spec, so I had to set it and the pail of TSP solution in the engine bay which was super awkward, especially when the fitting blew off and blasted TSP water everywhere.

All that to say, the probability of me trusting this thing for an overnight job is slim to none. I’d rather nuke my core with pure CLR for five minutes. I wish I could trust the setup overnight…

[fastboatster]

Originally Posted by KClemente

Here is a picture of when i did mine. I just moved the brace a little out of the way

thanks! this makes sense, it's much less of a hassle, like e90yyc, this way I won't feel obliged to get a new evaporator and condenser, andi go through the hassle of discharging and recharging the AC system, that's at least $250 to $300

[e90yyc]

Originally Posted by KClemente

Here is a picture of when i did mine. I just moved the brace a little out of the way

Forgot to ask:

How long did this job take you?

[tlow98]

Seems like you've covered your bases!

[KClemente]

Originally Posted by e90yyc

Forgot to ask:

How long did this job take you?

Looking at photo timestamps, it looks like it took me around 5-6 hours - with a lunch break in between.

As you can see in my photo, I never fully removed the dash brace. Just unbolted it and tilted it downwards as much as I could.

It's not pictured but I never even removed the center console. Maybe unbolted it but didn't take it out of the car.

I will say though, bending the coolant lines was easy, but aligning them back was a little tricky. A better way would be to just unbolt it from the firewall.

If I did it again, I'm confident I can get it done within 3-4 hours

[e90yyc]

Originally Posted by KClemente

Looking at photo timestamps, it looks like it took me around 5-6 hours - with a lunch break in between.

As you can see in my photo, I never fully removed the dash brace. Just unbolted it and tilted it downwards as much as I could.

It's not pictured but I never even removed the center console. Maybe unbolted it but didn't take it out of the car.

I will say though, bending the coolant lines was easy, but aligning them back was a little tricky. A better way would be to just unbolt it from the firewall.

If I did it again, I'm confident I can get it done within 3-4 hours

That sounds reasonable. Even if it takes me 6-8 hours, each core flush has probably taken me 3 hours due to setup, cleanup, bleeding, etc, so just going straight to core replacement is probably the move.

Got any more pics? And if so, would you mind sharing them (can just provide a link—whatever’s easiest).

Thanks again.

[krhodes1]

I'll add that if it were me, given your evaporator is 11 years old now, I would absolutely replace that too while I was in there. Especially since the system has to be evacuated anyway if you are taking the dash out and not trying to get the heater core out the side.

I really need to do the flush in my 128i, the heat in it is quite poor. But here in SW Florida it's a tad less urgent than in Canada. When we had our 10 days of frigid 45F temps in January, I just drove my Mercedes.