How to fix leaking bulkhead couplers
I had to change the O rings on the heater matrix bulkhead couplers yesterday. They had become flattened and were not sealing properly. I was getting occasional wiffs of vapour coming through the air vents and a film residue on the Windows that was difficult to clean off. This is antifreeze residue and probably not good to breathe in either. The other symptom is a slow loss of coolant with no obvious leak.
This fix costs pence but the fault could easily get misdiagnosed as a leaking heater matrix at much expense!
I'd seen this with my S3 but the O rings were also obviously worn and disintegrating. The TT's 28 mm OD O rings were showing absolutely no signs of wear and looked perfect apart from their shape which had a flat on the inner and outer edge measuring 3.2 mm across flats but 3.7 mm front to back.
This makes me wonder what will happen to all the push fit plumbing solutions being installed into houses. Good stored up work for plumbers and decorators after several years I think :wink:
![Image]()
![Image]()
Fixing or changing the couplers is simple. You don't need to remove anything major to gain access which you gain from the engine bay behind the engine high in the middle the bulkhead..
You need to cut a cable tie and unclip the silver heat shield wrap around the hoses. A pair of pliers for the hose spring clips will remove the hoses but it might be easier to pull the couplers off the heater matrix first as you can pull the hose to do it.
If you are only changing the O rings you can leave the couplers clamped into the hoses.
To disconnect the couplers from the heater matrix, pull the spring clip back with a screwdriver. They should retract down. Feel underneath with a small flat bladed screwdriver. The spring clip only retracts so far and locks expanded. Make sure you don't ping it off and lose it! See the pictures. The lower one shows the middle of the spring going across from one side to the other, under which you need to lever and also showing the spring sides that lock onto the matrix pipe. The top picture shows the side where there's a small groove that latches the clip wire end, expanded in the unlocked position.
![Image]()
![Image]()
Then pull the coupler and it's off. Undo the hose clip if changing the couplers. Do one at a time so you don't mix up in and out but it probably doesn't matter.
The O rings can be removed from their internal groove with a small screwdriver or wire hook. You can keep the couplers on the hoses to do this as the pipes are flexible. Face them towards you and give them a clean with IPA and kitchen roll wiped round to remove any dirt. Push the new O rings into the grooves.
Lubricate the O rings with coolant for easy refitting of the couplers back on the matrix.
The couplers can be refitted with the spring clip engaged (it expands) or retracted which is easier but you need to press it back with a snap - simple
I had to change the O rings on the heater matrix bulkhead couplers yesterday. They had become flattened and were not sealing properly. I was getting occasional wiffs of vapour coming through the air vents and a film residue on the Windows that was difficult to clean off. This is antifreeze residue and probably not good to breathe in either. The other symptom is a slow loss of coolant with no obvious leak.
This fix costs pence but the fault could easily get misdiagnosed as a leaking heater matrix at much expense!
I'd seen this with my S3 but the O rings were also obviously worn and disintegrating. The TT's 28 mm OD O rings were showing absolutely no signs of wear and looked perfect apart from their shape which had a flat on the inner and outer edge measuring 3.2 mm across flats but 3.7 mm front to back.
This makes me wonder what will happen to all the push fit plumbing solutions being installed into houses. Good stored up work for plumbers and decorators after several years I think :wink:
Fixing or changing the couplers is simple. You don't need to remove anything major to gain access which you gain from the engine bay behind the engine high in the middle the bulkhead..
You need to cut a cable tie and unclip the silver heat shield wrap around the hoses. A pair of pliers for the hose spring clips will remove the hoses but it might be easier to pull the couplers off the heater matrix first as you can pull the hose to do it.
If you are only changing the O rings you can leave the couplers clamped into the hoses.
To disconnect the couplers from the heater matrix, pull the spring clip back with a screwdriver. They should retract down. Feel underneath with a small flat bladed screwdriver. The spring clip only retracts so far and locks expanded. Make sure you don't ping it off and lose it! See the pictures. The lower one shows the middle of the spring going across from one side to the other, under which you need to lever and also showing the spring sides that lock onto the matrix pipe. The top picture shows the side where there's a small groove that latches the clip wire end, expanded in the unlocked position.
Then pull the coupler and it's off. Undo the hose clip if changing the couplers. Do one at a time so you don't mix up in and out but it probably doesn't matter.
The O rings can be removed from their internal groove with a small screwdriver or wire hook. You can keep the couplers on the hoses to do this as the pipes are flexible. Face them towards you and give them a clean with IPA and kitchen roll wiped round to remove any dirt. Push the new O rings into the grooves.
Lubricate the O rings with coolant for easy refitting of the couplers back on the matrix.
The couplers can be refitted with the spring clip engaged (it expands) or retracted which is easier but you need to press it back with a snap - simple
