1.9 TDi coolant loss

[MTBPhil]

I think this will be a lost cause because looking at the vw audi forums this is a hugely common issue.. but I thought I'd ask to see if anyone else has had this issue.

2005 caddy Van 1.9 tdi engine
When I got the van the headgasket had gone - no hot air from blower, pressurised coolant tank

I replaced the head gasket, water pump, cam belt, thermostat - and also swapped the head as mine was in very poor condition for a good lower mileage head.
I didn't skim the head as I read you shouldn't - I just bought one which was checked with a mechanics straight edge to be perfectly flat (that being said I do not know if it had been previously skimmed but it didn't look like it had)

Everything was perfect after that for about 6 months until last summer it started losing coolant - about a full expansion tank every few months
I checked every pipe, there was no visible leaks, I changed both temp sensors with new o-rings just to be safe - no coolant on the floor, no smoke from the exhaust, no coolant in oil or oil in coolant, no pressure in expansion tank

The only thing I could see was some dampness on top of the gearbox - so I swapped the plastic connector on the passenger side of the head for a new one as it looked like the o-ring was fairly flattened and hard.

The coolant loss seems to be getting worse - I can do about 300miles of motorway cruising at 70 and the tank is empty, but I still can't see any leaks from anywhere. Radiator seems fine, hoses seem fine, undertray is bone dry.

I really can't bring myself to believe it's cylinder head related as it was fine for 6 months after the head swap and new head gasket etc... as mentioned.

Is there anything else I could look at?
Thanks

[Doc]

A phantom coolant leak like that is very often the EGR cooler. It leaks only when the coolant and exhaust are hot so it turns the coolant to steam which is great for cleaning your inlet manifold.

[MTBPhil]

Oh sorry I knew I'd forget something

It's had a full EGR delete with darkside stuff too

[Doc]

In that case a pressure test is your best method to find the leak.

[Scoobysrt]

Same thing happened on my 1.9, I eventually found it to be the bottom radiator connector had cracked slightly where the hose met it I changed the radiator and it cured it. The leak would only happen when it was hot.
The other thing is to make sure your footwells aren't getting damp or you have a misted up windscreen when it's running hot (heater matrix gone).

[MTBPhil]

Thanks mate I’ll have a look.

I did notice when it froze that there was ice inside the windscreen!
Which made me wonder about a leak internally. But no smell, carpets are dry and I replaced the heater core before I did the head gasket.

I would have thought the 2 litres of coolant if leaking inside would have left some signs.

I should say there’s no issues at all with how the van runs, and no overheating at all since doing the head and head gasket.

It’s probably just as you say a plastic fitting that’s cracked and opening up when hot. I’ll whack it on axel stands at the weekend and take the undertray off and leave it running for half an hour.