Coolant low and seems to have sprayed side of car

[hewittinspain]

Following on from this thread I made regarding the dual climate not blowing hot air on the drivers side

Duel climate heating only heating passenger side.

Ive noticed today that the drivers side of the heating stays cool on my 14 plate FR, but on the passenger side it can be controlled properly. Having said that even on high temperature the passenger side isn't as hot as it seemed to be before but its still ok. Ive tried turning the engine on and...

www.seatcupra.net

I have since run into a new problem, maybe linked with the heating issue. Today I was driving on the A1 when I got a warning of LOW COOLANT and then a red triangle came on. I came off the A1 immediately and phoned my breakdown cover. In the meantime I restarted the engine and the light had gone out but had noticed that the coolant has gone from the expansion tank and there were coolant sprays on the side of my car. The temp guage was still showing 90 degrees so it doesn't look like my engine has overheated. The coolant was on maximum a week ago.
The tow guy told me to buy a new expansion tank and coolant and get someone to fit it (as its a 5 min job). Later on a friend through a spanner in the works when I called him as he said it could be the head gasket ??. Im no mechanic by any means but I checked the oil and there is no white residue at all and no white smoke coming from the exhaust.
Does anyone have an idea what my problem may point to? Does it sound like it just needs a new expansion tank? I dont want a garage to mis-diagnose the issue and go for the most expensive option plus I dont think I can drive the car now there is no coolant in there so would may need to find a mobile mechanic.
My earlier issue (on the link) was that the duel heating wasnt blowing hot air on the drivers side which may have been a matrix issue but do you think the two problems are now linked?

 

[black_sheep]

I had this exact same issue on my 184 ps Octavia.

Always passed the pressure (coolant)/compression tests, no exhaust contaminants in coolant/no milky residue in the oil - ie. unlikely to be head gasket.

I had a catastrophic failure of the water pump too (another common fault) which just just delayed establishing the root cause.

I traded in the car, but soon after, the known issue with the blocked heater matrix was better understood.

Replacing the expansion reservoir and cap are relatively cheap, but I would I think that the heater matrix is the most likely.

 

[BillyCool]

Read this thread (there are also others)

silica grain in the header tank

I am seeing a lot of comments on VW / Audi and Leon sites about heating matrix needing sorting. I personally have so far had no issues with this at all but I also see a lot of people commenting on removing the Silica grain bag in the header tank. Anybody got any information. TIA.

www.seatcupra.net

The blocked heater matrix causes the coolant to overheat during a DPF regen and it shoots out of the relief valve under the expansion tank lid. The issue can be confused by a faulty water pump as @black_sheep commented.

When my car had similar issues, I ended up replacing the matrix and water pump. The pump was indeed faulty and causing overheat issues, but the blocked matrix was causing the coolant loss. Both happening at the same time made fault finding a bit harder.

It can easily be diagnosed as a head gasket issue but if you have no obvious signs of that I'd go down the matrix route first. After all, on your previous post it was touched upon as a likely issue. You just hadn't had the coolant loss, but now you have.