VW Passat 2016 TDI - Heater blowing cold air

Fernagx

Hi,

I recently had my VW Passat TDI 2.0 2016 serviced. Before doing so, I told the mechanic that the heater was blowing out cold air when the heat was turned to max and the fan was turned up. So I asked him to take a look.

He advised that the coolant pump was leaking and that this could be the cause. So I got that the fixed but the issue still persists.

The mechanic advised that all the right pipes are getting hot so heat is definitely being generated. He thinks that it may be problem with the temperature dial in the car but he couldnt say for sure. And he didnt want to take out the whole dash if that wasnt the issue. So he advised me to speak to VW and see if there was anything on forums where it may be a simpler fix.

I should say that if the heat is turned up to max and the fan setting is on 1, the heat coming out the fans is quite warm. Its just when you turn up the fan then you can definitely feel cool air.

Any help would be much appreciated.

Heckler

Hi,

This will be of no use to you at the moment but I had the exact same problem before either with a VW golf or an Opel Astra can't remember which.

I do remember in my situation it had nothing to do with the temperature dial but I also remember it was an easy fix once diagnosed just can't recall what it was ! It'll come to me hopefully and I'll let you know. Good luck with it.

mk7r

Heater matrix is likely blocked due to the silica bag in the coolant bottle after bursting, not a cheap fix unfortunately. See recent threads here about the same issue

Fernagx

Thanks can you direct me to the recent threads please?

mk7r

Sure, this is for a golf but same setup in your Passat

https://www.boards.ie/discussion/2058270165/golf-blowing-only-cold-air#latest

CoBo55

Is the coolant dirty/sandy looking? A reverse flush of the heater matrix might help temporarily. You're in trouble I'm afraid.

Fernagx

Hi,

So I took it to two local mechanics. One tried backflushing. It improved the situation slightly but its still not great - they recommended taking it to VW Frank Keane at Liffey Valley who have a system that does a full flush of the system and replace the heater core. I got a quote and they are charging €1,800 which is astronomical.

colm_mcm

There is a specific process to follow to clear the system, and it’s time consuming.

Try Daltons in Portlaoise. They know their VWs

mk7r

https://www.boards.ie/discussion/comment/121510848#Comment_121510848

The special VW fluid is very expensive (hundreds) and doesn't always work, matrix replacement is often necessary

Fernagx

The core was replaced by a local mechanic. But VW still want to replace it again (according to their diagnostic). That's only 200 in the grand scheme.

The local mechanic advised that the previous Owner put Radwell in which seems to have clogged the system.

jmreire

https://www.boards.ie/discussion/comment/121511938#Comment_121511938

Radweld (to give it its proper name) should not be left next or near any ICE engine.INMHO. Looks like you have a silicate problem, I guess that the thermostat has been checked ?. It would be on the list of things to check. See if any of the garages you took it to, checked it out? I've replaced the expansion tanks my own and the Wifes Superb. €30 each last year, as I could not remove the silicate bags in the original expansion tanks.

Fernagx

It's not the thermostat. If I put it on setting 1, the heat is pretty decent from one vent. But as you increase the setting it goes to warm, then lukewarm and so on.

I'm actually ok with it. It's just that I have two young boys and a wife. We've been lucky this winter so I'm more concerned when it gets to subzero temperatures

jmreire

Well, if the Thermostat is OK, the "hot" pipe from the engine feeding the heater matrix is hot at the matrix entry point, then we have to assume that the problem is from that point on IE:- the matrix itself. There's been several suggestions in the previous posts about what to do about that, from flushing it out to replacing it (and the expansion tank too, while you are at it) So you will have to choose which is the best option for you. Sorry I can't be more helpful, but Best of Luck with it.

Vic_08

https://www.boards.ie/discussion/comment/121512074#Comment_121512074

The blower setting just changes the fan speed, it has nothing to do with the thermometer or the heat flowing through the matrix.

On 1 the fan blows a small volume of air and if the matrix is lukewarm it will heat up that air, on higher settings the volume of cold air being forced through will overwhelm the matrix and the air will not heat up much. It is consistent with a matrix that is gunged up and not getting proper flow of hot coolant.

alexago

It's frustrating that the issue with your VW Passat's heating system persists despite fixing the coolant pump. Since the mechanic suspects a potential problem with the temperature dial, it may be worth checking the owner's manual for any troubleshooting tips. Here I can suggest checking https://www.vwmanuals.org/ I found mine there. Otherwise, I'd recommend searching online forums or contacting VW directly.

CoBo55

https://www.boards.ie/discussion/comment/121516277#Comment_121516277

🤔

He has been told it's a sludge issue, changing the water pump will make no difference. The whole cooling system needs to be properly flushed and cleaned out and to get a completely successful outcome the heater matrix should be replaced as it can never be fully cleaned by flushing.

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