Weird flushing sound after heater matrix replacement

Aero843

Active Member
Feb 23, 2021
30
7
I'm having problems with my coolant system after replacing the Heater Matrix. dropped the rad hose and everything and drained, left the cap on heat full on till it got up in temps to 90 to get air out, topped up with coolant as the coolant went around the system but now I'm getting noises as seen in the video? any help appreciated
https://www.youtube.com/shorts/ATZ8mmkf85c
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
I'd think that you still have air trapped within the coolant system, I bought a Draper Coolant Vacuum Refill Kit not because I wanted to, but because I thought that I would need that when I replaced the coolant after fixing a slight leak in my old S4, that worked okay, or at least I probably ended up with less air trapped initially, when I dump the G13 out of my wife's 2015 VW Polo I'll probably need to use that to minimise the chances of ending up with air trapped in its coolant system.
Eventually your system might end up purging itself of all trapped air, some earlier cars with the old 1.4 16V 86PS petrol engine were tricky to get rid of trapped air, I ended up finding out that the only or best way to refill that engine's cooling system was to remove the engine coolant sensor and refill the system with that out and continuing to refill once only coolant was coming out while refitting that sensor, a bit tricky doing that yourself, but it worked first time after failing to get rid of the trapped air by driving it a few times!

Edit:- maybe tell us which engine is fitted to that car, it does sound a lot like it is a TDI though!
 
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Aero843

Active Member
Feb 23, 2021
30
7
I'd think that you still have air trapped within the coolant system, I bought a Draper Coolant Vacuum Refill Kit not because I wanted to, but because I thought that I would need that when I replaced the coolant after fixing a slight leak in my old S4, that worked okay, or at least I probably ended up with less air trapped initially, when I dump the G13 out of my wife's 2015 VW Polo I'll probably need to use that to minimise the chances of ending up with air trapped in its coolant system.
Eventually your system might end up purging itself of all trapped air, some earlier cars with the old 1.4 16V 86PS petrol engine were tricky to get rid of trapped air, I ended up finding out that the only or best way to refill that engine's cooling system was to remove the engine coolant sensor and refill the system with that out and continuing to refill once only coolant was coming out while refitting that sensor, a bit tricky doing that yourself, but it worked first time after failing to get rid of the trapped air by driving it a few times!

Edit:- maybe tell us which engine is fitted to that car, it does sound a lot like it is a TDI though!
Oh ye forgot to mention, its a 2.0 tdi 184, I am just paranoid the coolant is getting around all the system and somewhere is getting no coolant and is just gonna burn out or something 😂😂
 
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BigJase88

Jase
Apr 20, 2008
3,767
1,069
When you were bleeding it with the cap off did you also have the heating set to max?

Also check coolant hoses as they head through the bulkhead and make sure both flow and return are hot.

Squeezing / pumping these hoses here with the cap off is also a good way to force trapped air out
 
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RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
@BigJase88, do these cars not just use "air blending" to control the air temperature, ie they just use flaps to direct/divert the incoming air?

The generic instruction to "set heating to max" in this situation is only relevant to cars that have a thermostatic valve controlling coolant flow through the heater matrix.
 

BigJase88

Jase
Apr 20, 2008
3,767
1,069
@BigJase88, do these cars not just use "air blending" to control the air temperature, ie they just use flaps to direct/divert the incoming air?

The generic instruction to "set heating to max" in this situation is only relevant to cars that have a thermostatic valve controlling coolant flow through the heater matrix.
No idea.

It's just something i have always done on every car.

🤣

Probs stuck in the past
 

Yern

Active Member
Apr 25, 2019
625
311
(Set heating to max) Ah the old days, just a piano wire cable was all you needed for heat...
 

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SuperV8

Active Member
May 30, 2019
1,318
578
@BigJase88, do these cars not just use "air blending" to control the air temperature, ie they just use flaps to direct/divert the incoming air?

The generic instruction to "set heating to max" in this situation is only relevant to cars that have a thermostatic valve controlling coolant flow through the heater matrix.
They do - but it actually says to set heating to max in the workshop manual (from memory)
There is a separate electronic pump for the micro circuit - (heater matrix & EGR cooler circuit) which I may be activated when heating demand is requested.
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
They do - but it actually says to set heating to max in the workshop manual (from memory)
There is a separate electronic pump for the micro circuit - (heater matrix & EGR cooler circuit) which I may be activated when heating demand is requested.
I agree about the comments still being included in the official workshop manuals, but like a few other of similar comments/instruction, I think that this is just legacy stuff, being copied and pasted by lazy or not quite technical enough technical authors.
 

mykro

Active Member
Apr 12, 2022
73
7
I'd think that you still have air trapped within the coolant system, I bought a Draper Coolant Vacuum Refill Kit not because I wanted to, but because I thought that I would need that when I replaced the coolant after fixing a slight leak in my old S4, that worked okay, or at least I probably ended up with less air trapped initially, when I dump the G13 out of my wife's 2015 VW Polo I'll probably need to use that to minimise the chances of ending up with air trapped in its coolant system.
Eventually your system might end up purging itself of all trapped air, some earlier cars with the old 1.4 16V 86PS petrol engine were tricky to get rid of trapped air, I ended up finding out that the only or best way to refill that engine's cooling system was to remove the engine coolant sensor and refill the system with that out and continuing to refill once only coolant was coming out while refitting that sensor, a bit tricky doing that yourself, but it worked first time after failing to get rid of the trapped air by driving it a few times!

Edit:- maybe tell us which engine is fitted to that car, it does sound a lot like it is a TDI though!
Do you mean coolant temperature sensor at engine block ? Because when I pull off sensor attached to radiator, it will bleed only cca 3.5l from entire 10l. 1.8tsi 2015
 

RUM4MO

Active Member
Jun 4, 2008
7,784
983
South Scotland
Do you mean coolant temperature sensor at engine block ? Because when I pull off sensor attached to radiator, it will bleed only cca 3.5l from entire 10l. 1.8tsi 2015
That comment I made was concerning an older engine that was known to be difficult to refill, even although its cooling system was basic, and that is mainly the problem with newer engines, their cooling systems are getting quite complicated - well at least when it comes to refilling the cooling system. So, with some models, you do need the manufacturer's diagnostic tool to enable electric coolant pumps and open any electric isolation valves in the system, as well as using a vacuum re-filling system.

All very annoying for the home car mechanic DIYer.
 

Aero843

Active Member
Feb 23, 2021
30
7
When you were bleeding it with the cap off did you also have the heating set to max?

Also check coolant hoses as they head through the bulkhead and make sure both flow and return are hot.

Squeezing / pumping these hoses here with the cap off is also a good way to force trapped air out
Ya I took the cap off and put the heating on max and let it run for about 30 minutes, Noise is still there everytime engine is turned off so not sure 😂
 
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