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Old 02-17-2020, 10:39 PM   #1
Hot_tub
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WHY did my heat slowly turn cold? After it was warm at idle/first test run?

I just replaced my expansion tank, upper radiator hose, thermostat and bled the system 'properly'.

I jacked the car up at an angle to keep the ET Fill / Bleed screw the highest point. I turned the heat up to 91, fan on 1 line and filled it to the brim. I waited 5 or so minutes for all bubbles to come out then siphoned the excess ET coolant out to a little under Max Coolant.

I closed up the bleed screw and ET then let er rip. I was checking for leaks for about 4 or 5 minutes up and down and didn't see a drop. I peeked my head in the car and it was blowing out very hot air and continued to blow out hot air until it peaked around 98C. it never went above, Perfect!

I took the care for a short couple mile spin and everything was perfect. Once i got home i parked it up for an hour or 2 to let it cool down. I checked the coolant level at around 62C and as i opened the ET i heard a distinct hiss sound like i broke the seal. Since then i noticed after a good 20 minute drive the heats intensity slowly diminished. Once i got back home, at idle the heat was only about lukewarmish/semihotish. Still a bit of chill to it.

I googled if it lets air into the system when opening the ET, but apparently it doesn't?

Did me cracking open the still warm ET let air into the system?

I don't see any wet spots either.
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Old 02-17-2020, 10:56 PM   #2
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Worth noting waterpump was replaced last year with

https://www.ecstuning.com/b-geba-par...517527910~geb/
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Old 02-18-2020, 03:59 AM   #3
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Rebleed the cooling system. You still have air in the system.
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Old 02-18-2020, 06:02 AM   #4
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what was the coolant level AFTER the lukewarm experience? You didn't mention it. The lack of heat in this situation, sounds a little like a low coolant situation. So you could have had a bubble, coolant level looked fine, then bubble escapes and actual coolant level is too low.

The hissing sound when you opened your ET was a good sign/sound as it indicates its holding pressure.
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Old 02-18-2020, 07:27 AM   #5
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Just checked the level and it seems to be right above min, maybe a half inch above min... Interesting.

Did i do something wrong with my bleed? Was there air trapped behind to thermostat perhaps?

That being said should i rejack the car up, fill it high and bleed/siphon it again?

Also good news to hear about the hiss being a good sign, can you confirm this isn't letting air in? Only the bleed screw would let air in if my research serves me well, correct?
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Old 02-18-2020, 07:29 AM   #6
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Sounds like you've bled the system correctly.
Albeit I completely fail to understand why some videos and/or aftermarket repair manuals suggest having the KOEO and the heat set to XXX. Totally unnecessary. With the key off/removed the heater control valve has no power. As has always been the case with BMW's the heater valve is forced to close with power, if there is a failure of power (for whatever reason) or the key is off the heater valve is OPEN.

German engineering @ work. The system is always capable of providing heat.
If the E46 had an auxiliary coolant pump (it does not!) the KOEO and heat settings set to warm apply. Aux pumps are a friend, albeit the E46 is bereft of such.

I've also noticed a penchant of some to continuously open up the bleeder screw and re-bleed the system. Generally not needed. (Although in your case apropos)

One fills the system as you did with the bleeder open, fill and wait. Once it purges the air, the system should be at least 80+% full. There is a crossover between the upper hose to the tank. That's where you see the coolant return to the tank with the cap off and revving the engine slightly. If the system is mostly full and the water pump working correctly it will purge any air back to the expansion tank.
Aggressive drive, heat on and monitor coolant temps in the cluster test #7. The best way is to let the car cool completely and then remove the cap to double check the coolant level.

Repeat the bleed procedure as you did before, this time with the key removed. Drive the car and watch the coolant temps making sure the thermostat opened: Cold, warmer, then hot and finally a large reduction in displayed temperature. This lets you know that the thermostat has opened for the first time (an important distinction most skip) promoting a complete circulation of the coolant circuit.
Drive home and let cool COMPLETELY. Then remove the cap and correct coolant level as needed.

Report back.
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Old 02-18-2020, 08:50 AM   #7
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Just checked the level and it seems to be right above min, maybe a half inch above min... Interesting.

Did i do something wrong with my bleed? Was there air trapped behind to thermostat perhaps?

That being said should i rejack the car up, fill it high and bleed/siphon it again?

Also good news to hear about the hiss being a good sign, can you confirm this isn't letting air in? Only the bleed screw would let air in if my research serves me well, correct?
With coolant right ABOVE min, your lukewarm heat is not due to insufficient coolant in the system.. You may have a bubble..

I can pretty much confirm that the hissing is not letting air in, that would mean suction or neg pressure. You won't create an air bubble by opening the expan tank.
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Old 02-18-2020, 09:07 AM   #8
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My turkey baster needle fell off into the ET.


K.

Now i have to pull it and shake it out as a skinny magnet isn't grabbing it.. K.
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Old 02-18-2020, 09:17 AM   #9
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Just pulled the tank and shook it upside-down and it dropped out and pinged as it hit the pavement, thank god. What a pain in my ass.

Back to square 1.
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Old 02-18-2020, 10:41 AM   #10
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First update:

Just got back from a grocery run (10 minutes to, 10 minutes from) The thermostat opened once on the way there and once on the way back after it was sitting for 10 or so minutes while i shopped. I noticed the heat stayed warm for the most part, maybe the slightest change but nothing terrible. Still very warm. It then rose to a sort of scorch level and bounced between those two ranges. I'm happy with this result if it lasts.

So the next instructions are to wait for it to get to roughly ambient temp and then open the tank and check the level?
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Old 02-18-2020, 11:04 AM   #11
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Just pulled the tank and shook it upside-down and it dropped out and pinged as it hit the pavement, thank god. What a pain in my ass.

Back to square 1.
you are becoming an expert on cooling system disassembly.
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Old 02-18-2020, 11:07 AM   #12
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you are becoming an expert on cooling system disassembly.
Haha yes, I just replaced it not too long ago as the (seems like) OEM one burst after nearly 16 years of service. That was not a fun day.
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Old 02-18-2020, 12:07 PM   #13
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Keep monitoring the level in ET until it's stable...consistently on level ground.

I suspect your drive is what knocked the bubbles out...and your level will drop for a few trips at least as the air gets knocked out of the system from driving at speed.

Keep an eye on it closely until you know you're good.
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Old 02-18-2020, 12:15 PM   #14
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The remaining air is being relieved through the ET cap correct?
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Old 02-18-2020, 07:52 PM   #15
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The remaining air is being relieved through the ET cap correct?
The remaining air is trapped in the tank, the cap doesn't vent until the pressure reaches 2 bar or 29 psi. Which is higher than normal operating pressures. I have a 1.4 bar cap and it has never vented. If it hisses when you open the cap after sitting overnight the pressure is just equalizing. If it's cold out the air is most likely going in, don't worry about it. After a few nights the level should stabilize, usually takes mine about three days. Never had my heat level drop while driving, sounds like your thermostat isn't closing fast enough to maintain heat levels.
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Old 02-18-2020, 08:11 PM   #16
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I had a problem where my heat would work fine during short drives but at some point it began to fade during longer drives. Eventually the heat would stop working after about an hour drive. It turned out there is a fan and temperature sensor that is part of the HVAC panel on the center dashboard that failed. This meant the entire HVAC panel (it has all the HVAC buttons and displays the desired temperature) had to be replaced because the fan and sensor are not available separately. You may very well just have air in the system but your symptoms reminded me of the problem I had so I thought I would put it out there.
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Old 02-18-2020, 09:18 PM   #17
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I'm almost not sure if i should crack the ET cap or not to check the level. And don't if it's cold out?

It's been blasting hot and i believe what i did differently this bleed is that i keep pouring even after coolant was pouring out of the bleed screw. Bubbles kept on popping for about 20 seconds, then it was a smooth flow of coolant.

If my memory serves me correctly i think i stopped filling as soon as i saw coolant come out of the bleed screw and said to myself "Well that must be full since it's the highest point on the car".

I know i'm not leaking (unless theres a pinhole somewhere somehow)
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Old 02-18-2020, 09:51 PM   #18
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The remaining air is trapped in the tank, the cap doesn't vent until the pressure reaches 2 bar or 29 psi. Which is higher than normal operating pressures. I have a 1.4 bar cap and it has never vented. If it hisses when you open the cap after sitting overnight the pressure is just equalizing. If it's cold out the air is most likely going in, don't worry about it. After a few nights the level should stabilize, usually takes mine about three days. Never had my heat level drop while driving, sounds like your thermostat isn't closing fast enough to maintain heat levels.

but since you say don't worry about it...
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Old 02-18-2020, 10:00 PM   #19
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I'm almost not sure if i should crack the ET cap or not to check the level. And don't if it's cold out?

It's been blasting hot and i believe what i did differently this bleed is that i keep pouring even after coolant was pouring out of the bleed screw. Bubbles kept on popping for about 20 seconds, then it was a smooth flow of coolant.

If my memory serves me correctly i think i stopped filling as soon as i saw coolant come out of the bleed screw and said to myself "Well that must be full since it's the highest point on the car".

I know i'm not leaking (unless theres a pinhole somewhere somehow)
ambient air, hot or cold, introduced while opening the ET will in no way going to create bubbles. air is not going to find its way and cut thru coolant
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Old 02-19-2020, 12:29 AM   #20
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Interesting.

Will cracking the cap and getting the hiss make any existing air more exacerbated and apparent since the 'vacuum' is interrupted?
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