Hi all,

 

As the colder UK weather has returned I've been faced with troubleshooting a problem in my other car (VW Golf Mk7) that shares the same engine that's in my Superb. Recently we've noticed the cabin heater when turned to full blast on hot, initially gives a belt of warm air then soon changes to luke warm. Turn it back down to the lower setting and it seems to remain hot.

I did some searching through all sorts of forums and it seemed to me that the problem may be related to the heater matrix. Today I removed the two pipe connections in the engine bay that lead through to the heater matrix and began to flush it through with clean water. All that came out was a bit of red coolant, possibly a little bit of silt but was free flowing. It certainly wan't full of the crap I've seen some folks videos demonstrate. This made NO difference to the issue and the problem remains. Strangely the water level in the expansion tank did not drop at all but maybe some of the water I used to flush was still in the heater matrix.

 

I moved onto trying to flush the coolant system as the car is 10 years old and I'm not certain it would ever have been done. I added some additive, ran it for 10 mins and removed one of the lower radiator pipes to let the fluid out. Strangely I could only get 1-2 litres out and that's it. I put some water back in and re-ran the car some more, and i could see the water was being circulated with more red coolant. I flushed that out and repeated a couple more times.

 

For now I've refilled the system as I can't get to the bottom of this issue.

 

The bottom radiator pipes always remain cold and i'm not sure if that is normal?

 

The car temperature behalves normal as far as I can tell and moves religiously to 90 and stays there. I can't get the car engine hot to the point it triggers the engine fan and to be fair this has applied to all diesel engines i've owned apart from when its mid summer with high temperatures. With current 4 degrees weather I've got little chance of getting it really hot!

 

The cambelt was changed this year along with a new water pump so i'd like to assume the water pump is OK. I did try pressing the accessible coolant pipework when the engine is running and i can squeeze them quite easily - this seems the same on the Superb when i perform the same check so assume this is normal.

 

VCDS doesn't show any errors.

 

Comments appreciated.

 

I'm no expert but having had issues with my heater matrix I have a little experience. Mine was blocked due to the water pump breaking up and corrosion (according to the garage anyway). I changed the heater matrix myself so an easy enough job for a diyer, although I cursed a lot. Anyway, I found I got some heat through the blowers when running very slow but as soon as I turned the fans up the increase in airflow was too much for the matrix to heat up so turned cold - sounds similar to what you describe. I'd suggest changing the heater matrix and see what that does for you, I think it cost me £120 for the matrix but it fixed the issue straight off for me.

I should've said.... I was able to flow water through my clogged matrix btw, I assume it just wasn't able to get into the much finer elements but could bypass them through the larger pipes around it, but again I'm guessing.

Ok that’s a fair comment, it has been playing on my mind that this could still be a problem. My only issue will be finding the correct part number for the heater matrix as VW never want to tell you.

I also saw a video on YouTube where a chap had cut the end off a bad heater matrix to show its insides. Interestingly he said when it is partially blocked you can get symptoms where for example the side vents are cooler than the air on the central console. This is just like what I’m experiencing.

 

Looks like a new heater matrix is in order then.