Slow cabin heat - again

[ervybaby00]

Hi,
I thought I had permanently fixed a slow cabin heat issue by replacing the heater core in 2020 but the same problem is back again. My car was post-warranty and I somehow managed to get VW Canada to pay for half the repair since the problem had started during year 4. The engine temp goes up to half as expected after a few minutes (a little longer in very cold temp) but all I got was lukewarm air. The new heater core fixed the problem but now 3 yrs later the same issue is back. I have access to an Obd11 reader and would like to know what data to look for if that can indicate anything with a flap or sensor etc. Does coolant always flow through unsrestricted?
I also replaced a faulty water pump a few months ago. Coolant levels are still good.

Tnx.



Golf MK7 2015 Tsi manual transm.
Regular analog HVAC (not climatronic)

46,602 miles (75,000km)
Usage : 6,200miles per year approx
Cold winter months (-4 far. / -20 celc)

Yup I don't drive much...

 

[Jachas]

Does coolant always flow through unsrestricted?

In one world. No. Thermostat in this car is controlled by ECU. Heating is dependent from this thermostat, valve N422 and electric pump V51. You can check more info about cooling system in these engines (EA888 gen3) in SSP522.

In this cars (pre FL) had sometimes expansion tank with silica bag, which could clog heater core. Your expansion tank have "Mit Sillikat" stamped on it (google "golf mk7 mit sillikat) or had you changed expansion tank when changing heater core ?(I supose that only hearer core was changed,right?) If you still have "Mit Sillikat" expansion tank, you have both (exp. tank + heater core) + coolant to change

 

[ervybaby00]

In one world. No. Thermostat in this car is controlled by ECU. Heating is dependent from this thermostat, valve N422 and electric pump V51. You can check more info about cooling system in these engines (EA888 gen3) in SSP522.

In this cars (pre FL) had sometimes expansion tank with silica bag, which could clog heater core. Your expansion tank have "Mit Sillikat" stamped on it (google "golf mk7 mit sillikat) or had you changed expansion tank when changing heater core ?(I supose that only hearer core was changed,right?) If you still have "Mit Sillikat" expansion tank, you have both (exp. tank + heater core) + coolant to change

Tnx for replying.
My engine code is CXBA. I have Mit Silikat stamped on the expansion tank so it is possible that the silicate bag has opened up inside a long time ago.
I dont see it nor can i fish it out. When i changed the heater core 3 years ago i did not change the expansion tank. I didnt flush out the system either but full heat returned anyways. I want to rule out electronic failure (valve, pump, thermostat, or flap etc) before changing anything again.

 

[Jachas]

Take the lower center console cover (driver side) out. One torx 20 close to gas pedal and pull the cover out. After taking the cover out, you should see 2 metal tubes going to heater core. mr-fix made nice video about how to get to PTC (TDI only), between the tubes there are cables for PTC so you can use this video for reference.

If these metal tubes are hot, then all the valves, pumps, etc. is working fine and you have heater core clogged by silica from expansion tank, so New heater core + expansion tank + new coolant, to properly fix the issue

When searching for heater core, take in consideration that 2 versions of HVAC system was used (In europe at least). Denso or Valeo, and ETKA doesn't specify which one you have in car, you have manually confirm version mounted in your car. Or by checking producer logo on cabin filter cover, or the most secure, by checking by difference in piping (different routing of tubes between Denso and Valeo HVAC) When changing heater core i recommend heater core mounting kits from dealer (o-rings/sealings + new brackets and cost around 14$ en EU at least)

 

[YamR1rider]

Seems a post of mine was deleted, I can only guess because I linked a very helpful thread on another forum. But I and several others had the same issue and it turned out to be the N82 heater valve which restricts the flow to the heater matrix - they can fail in the closed position. Its a somewhat fiddly job but is certainly DIY doable. If you google N82 heater valve, the mentioned thread will likely come up in search results.

 

[ervybaby00]

Take the lower center console cover (driver side) out. One torx 20 close to gas pedal and pull the cover out. After taking the cover out, you should see 2 metal tubes going to heater core. mr-fix made nice video about how to get to PTC (TDI only), between the tubes there are cables for PTC so you can use this video for reference.

If these metal tubes are hot, then all the valves, pumps, etc. is working fine and you have heater core clogged by silica from expansion tank, so New heater core + expansion tank + new coolant, to properly fix the issue

When searching for heater core, take in consideration that 2 versions of HVAC system was used (In europe at least). Denso or Valeo, and ETKA doesn't specify which one you have in car, you have manually confirm version mounted in your car. Or by checking producer logo on cabin filter cover, or the most secure, by checking by difference in piping (different routing of tubes between Denso and Valeo HVAC) When changing heater core i recommend heater core mounting kits from dealer (o-rings/sealings + new brackets and cost around 14$ en EU at least)

Since some heat is already coming out of the heater core the difference in temperature will be between hot on one side and scalding hot on the other... It may be hard to tell but I will give it a try.

 

[Jachas]

temperature will be between hot on one side and scalding hot on the other.

Even both can have the same temperature. Recently i changed heater core clogged by sillica, and both tubes were hot (same or almost same temp. cause heater core was not "radiating" the heat to the cabin). But that means that all valves,pumps, etc. are working properly and lack of heat is caused by clogged heater core

 

[ervybaby00]

Even both can have the same temperature. Recently i changed heater core clogged by sillica, and both tubes were hot (same or almost same temp. cause heater core was not "radiating" the heat to the cabin). But that means that all valves,pumps, etc. are working properly and lack of heat is caused by clogged heater core

What method do you use to flush all the coolant out of both the radiator and the rest of the engine including heater core?

 

[Jachas]

Well, I you want flush all the coolant DIY, I think the most secure way would be multiple emptying and topping with distilled water until water becomes colorless, and when is only distilled water, one more emptying but topping it with G12Evo concentrate, because "VW way" is flushing with special tool (VAS 531 007) and use of 19L of distilled water and 18L of G12Evo collant


Last week I had '14 GTI for no heat in cabin, and in this car, apart from clogged heater core + "mit sillikat" expansion tank (after this 2, heat come back, but was not perfect, and with speed it was less and less heat), had N82/N422 valve stuck almost closed. Coil on the valve was good, so no errors on ECU, but valve was stuck. Only way to tell was to take it from car and check the valve manually


I personally think, that disconnecting lower radiator hose and both heater core hoses in engine bay + compressed air will do (+ compressed air in upper heater hose from engine bay to heater, to don't make the mess in legroom area inside the car when taking the heater core. In my experience, 99% of sillica goes to heater core, even is something will travel from engine block to heater, it isn't gonna be enought sillica to clog it.
And I do recomment to use vaccum filling tool, it makes life much easier and without problems with air trapped in coolant system

 

[ervybaby00]

Well, I you want flush all the coolant DIY, I think the most secure way would be multiple emptying and topping with distilled water until water becomes colorless, and when is only distilled water, one more emptying but topping it with G12Evo concentrate, because "VW way" is flushing with special tool (VAS 531 007) and use of 19L of distilled water and 18L of G12Evo collant


Last week I had '14 GTI for no heat in cabin, and in this car, apart from clogged heater core + "mit sillikat" expansion tank (after this 2, heat come back, but was not perfect, and with speed it was less and less heat), had N82/N422 valve stuck almost closed. Coil on the valve was good, so no errors on ECU, but valve was stuck. Only way to tell was to take it from car and check the valve manually


I personally think, that disconnecting lower radiator hose and both heater core hoses in engine bay + compressed air will do (+ compressed air in upper heater hose from engine bay to heater, to don't make the mess in legroom area inside the car when taking the heater core. In my experience, 99% of sillica goes to heater core, even is something will travel from engine block to heater, it isn't gonna be enought sillica to clog it.
And I do recomment to use vaccum filling tool, it makes life much easier and without problems with air trapped in coolant system

Tnx, you know what you're doing. What's your opinion on G13 vs G12evo vs off the shelf Euro purple brands?

 

[riceburner]

Sounds like the valve. Drivers side of engine block.

 

[ervybaby00]

Sounds like the valve. Drivers side of engine block.

Tnx- but a stuck closed valve would give me no heat, right? I am getting some heat still. My first heater core was clogged up and a new one fixed the problem but I forgot to flush the coolant and get rid of silica packet and so 2 years later same problem.

 

[riceburner]

hard to find my posts about it, but my 2015 R had the same issue where it would take like forever (like upwards of 20 minutes to get 'decently hot' air - when it should take like 5 minutes. it was 100% the valve - i suck at working with tight hard plastic coolant lines against the engine block but i had vw do it.

it was part # 4H0121671D, and cost $124.95 from ECS tuning back then in 2021. VW did the swap for me but for 300 dollars.

when they did it, and i picked the car up next winter morning, i had heat by the time i got out of the parking lot.

 

[YamR1rider]

Tnx- but a stuck closed valve would give me no heat, right? I am getting some heat still.

Not necessarily, no. When I was troubleshooting my system, after replacing the partially clogged heater matrix, I did get some heat after the car had fully warmed up - but weirdly only through some of the vents and fairly week. When I then replaced the N82 valve, the heat was there even before car fully warmed and through all vents.

 

[ervybaby00]

Turns out it was the N82 valve afterall. My garage started with a coolant flush and heater core change which didn't fix the problem (I changed the expansion tank to a silicate-bag free one). I inspected the previous heater core I installed and it is clear and functional! I asked him to check out the N82 valve. He bought an aftermarket piece and voila- heat again. The old unit was gunked up probably from whatever caused the first heater core to clog up. He asked if I ever put stop-leak inside the car but I never did that. Could have saved myself a bit more money 2nd time around by starting with the N82 but live-and-learn I guess (the idea was that I had neglected to flush out the coolant and change the expansion tank first time around when I changed the first heater core).