Technical Replacing heater matrix

[John202020]

£38 for the matrix, think its your year
https://www.ebay.co.uk/itm/BRAND-NE...rentrq:25e051b31770a6e5c55ecf3effa93105|iid:1

 

[ricky76]

Hi all.

I've been suffering with a heater matrix leak for about 3 months and decided to do something about it (finally).
Following the excellent info posted by John202020 access to the heater matrix was easy.

Next:

1/ Allow the car too cool down, then CAREFULLY remove the cap from the expansion bottle.

2/ The steel heater pipes come through the bulkhead (firewall to some) and are fitted to the heater matrix using two beige-coloured plastic clips. The heater pipes can be left in situ.

3/ Get a suitable bowl ready underneath (to hold about 2L of coolant), then carefully twist the clips undone. You might find that one side can be disengaged first, then spin the clip and undo the other side. Repeat for the lower connection.

Heater Matrix by P. Garry Ball, on Flickr

4/ The matrix "cassette" can be withdrawn easily for inspection.

2020-12-09_03-31-22 by P. Garry Ball, on Flickr

My matrix looked to be in excellent condition. My 2014 500S Twinair 85 has only covered 21k Miles so I was dubious about it having failed, plus
I have no means of pressure testing it at home. Closer inspection of the two beige clips though, revealed some pink staining on the pair from the lower pipe.

Next, I turned my attention to the two 'O' rings on the pipe ends. Removing both I noticed that they had both become very slightly distorted and a ridge had formed around the circumference of them both. I also noticed they had become a little hard (but not brittle).

Heater Matrix by P. Garry Ball, on Flickr

I wasn't able to find any suitable replacements in my usual stock of such things so it was off to Halfords.
They did a pack of 6 'O' rings in two sizes including 4 which looked about right (forgot to take my Vernier callipers with me).
(The Halfords stock code is HFX166)

Back home I measured the OEM O rings which were 20.0mm outside diameter and 1.8mm thick (item 2 in pic below) The Halfords ones were 17.5mm o/d and 1.7mm thick (item 1 in pic below).
I also bought some Granville Instant Gasket which is silicone-based and resistant to high temperatures, coolant and oil.

Heater Matrix by P. Garry Ball, on Flickr

I decided to do a dry fit of the new O rings. It was a slight stretch to get the Halfords 'O' rings over the water pipes.

Heater Matrix by P. Garry Ball, on Flickr

Once connected to the matrix and clips re-attached there seemed to be much more friction on the clips and they spun less easily than before.
This lead me to believe that the new O rings were under compression and my confidence in them working improved somewhat.

You'll notice that the clips have an inner moulded shape which matches the "trumpet" of the matrix pipe ends - make sure you have them the correct way round.

Heater Matrix by P. Garry Ball, on Flickr

I disassembled the whole lot again and smeared a decent fillet of instant gasket externally around the new O rings. Be careful if you use this stuff
not to let any get inside the water pipes as it could break away when set and potentially block up a water way.
Next I reassembled the whole lot - hopefully for the last time!

New coolant was then slowly added to the expansion bottle until it was full, I made sure the heater controls were fully open (HOT) Then I started the engine and let it run for ten minutes (with the pressure cap still off at this stage).
and periodically checked the level. Then, as the heater pipes warmed up I fitted the pressure cap and took the car for a run (there wasn't a need to bleed the system if the coolant is added slowly).
No leaks so far, but I've left all the trim off for now until it's been through a few heat/cool cycles and the instant gasket has cured.

I wonder how many other matrix's have been replaced when the issue was actually failure of the O rings?

I'll report back.

I've just completed a heater matrix replacement and found this thread really useful, but there is one important point that I thought would be useful to clarify.

On the newer Fiat 500 1.2 (mine is a 2014) the pipes fitted to the heater matrix are metal, and have a different size bore (larger). I looked online, and the only place I could get the OEM O-Rings from was the US. So I removed mine and measured them. Both the pipe OD and the heater matrix ID are 16.5mm.

The O-Rings shouldn't be replaced with some from Halfords, Eurocarparts or DIY stores, as unless it states otherwise, they are probably made from Nitrile. It's cost effective and cheap, but they are not manufactured to withstand the antifreeze chemicals, and would therefore be more prone to fail.

The O-Rings should be made of EPDM, but if you can't get hold of those, then FKM (Viton) will do (can withstand the same heat and chemicals, but is a stiffer rubber). I ordered some EPDM 70 Shore O-Rings in a 2mm Cross Section with a 16mm (ID) Bore, but I couldn't get the clips to seat back on the matrix and pipes, as 2mm was too thick. I also bought some in a 1.5mm Cross Section, but I was worried they would be too narrow. I think a 1.75mm Cross Section would be best, but I couldn't get any in that size.

So instead, I use some FKM (Viton) 75 Shore O-Rings in a 1.6mm Cross Section with a 16.1mm (ID) Bore. That fit perfectly, and although very tight, I was able to get the clips back on.

Prior to doing this repair, I was able to spin the clips, so the O-Rings had definitely failed. But the clips are now very tight and impossible to move so I am confident I have a very good seal. I would recommend sticking with 16/16.1mm to ensure a snug fit on the pipe.

For anyone interested, I bought the O-Rings from here: https://simplybearings.co.uk/shop/p...FKM-75-Shore-Rubber-O-Rings/product_info.html

Best of luck with your repairs.