Smell in cabin - process of elimination, any ideas?

[mikerajjers]

Hi all,
just a bit of background info first. Bought by 1.8T cabriolet back in Jan. Since then spent a small fortune getting it right (MAF, lambdas, engine mounts, brake pads, fixing massive oil leak due to dodgy rocker cover gasket, sparks, injector seals, boost valve) and now the engine is running well.

My main issue now is a 'sweet' smell in the cabin, which I can smell only when stationary, but not always, only sometimes. I had a petrol smell a few weeks back but that is gone since replacing injector seals. I'm well and truly stumped as to what it could be and whether I'm beginning to imagine things? I'm beginning to think it could be a dodgy filter somewhere, perhaps pollen? Or perhaps the aircon needs a good clean?

I thought it could be coolant leaking somewhere as I had quite a low level, which I topped up. But smelling the coolant from the bottle, it doesn't match the cabin smell. I thought it could be the heater system somewhere, but it is very intermittent and I parked it in my drive just now, engine running and could not smell it (even when putting the fans on max). Opened the bonnet and couldn't smell it either. Peeled back the plastic near the battery and no smell either. Also no obvious signs of any leaks anywhere.

As I couldn't smell it whilst stationary on driveway (engine running) but only when in town, I'm now thinking I may have been smelling fumes from outside. But surely there should be a filter somewhere?

Could it really be just an issue with a pollen filter and the aircon system needing a professional clean? What would you recommend checking?

Sorry for long winded post.

Thanks in advance

 

[desertstorm]

If it is losing coolant I would suspect the heater matrix has a small leak.
This could be intermittent dependent on the pressure in the system but is liable to get worse.
If the leak is slow it can evaporate almost as quickly as it leaks but as the leak gets worse you will notice it more.

Karl.

 

[mikerajjers]

I think you might be right, will it need to be done by a specialist using special tools or could I tackle it myself?

 

[VagCabby]

I'm going to say heater matrix as well. Coolant is the only thing that will have a sweetish smell to it unless someone has glued you carpet down with honey

 

[john777w]

Yes coolant has a sweet smell/taste, I would run the engine & feel around the heater/carpet area for any signs of fluid!

 

[mikerajjers]

Judging by the state the car was in when I bought it I wouldn't be surprised to find the carpet stuck down with chewing gum Found a replacement heater for £68+VAT locally and will pop over to Audi and get new clamps and gaskets for it. I'l have a stab at doing it myself.

 

[Mike_B]

Before you do, have a look at the flange at the back of the engine into which is plugged the temp sender - assuming the engine is essentially the same as the 2.0 petrol that is. These are known to crack - and /or the sealing ring for the sender fails - which was part of the source of my most recent problem with coolant loss.

The other sources of my coolant loss were the header tank cap, which had lost it's sealing ring - and it also turned out that the damn thing also needed a new header tank.

IF the heater matrix is leaking, then I'd expect evidence in the car, including condensation, but of course condensation may be less evident in a cab I guess.

Could someone have put some sort of freshener spray into the pollen filter? Perhaps in an attempt to clear a nasty niff from the aircon? A buildup of bacteria causes that - I believe there's a spray which you can get to kill them.

 

[mikerajjers]

I will check the flange during the weekend just in case, mines a 1.8t, but it is likely to be the same as yours. I've inspected the expansion tank and that seemed ok, the cap seemed to hold pressure ok as there was hissing when I unscrewed it.

I think it could be the heater matrix as the smell seems to originate fron the air ducts. I had the aircon and heating switched off all day today and didn't have any smell. As soon as I switch it on the whiff comes back. Nonetheless I've bought a replacement matrix which I'll hopefully get a chance to fit next week.

 

[john777w]

There's a fair bit online about cleaning the air con evaporator, this can cause a smell in the cabin, you can purchase a spray that kills off smells. If you do have a coolant loss, I would still go with the heater matrix.

 

[Ovid]

Check for stains on passenger seat and footprints on roof lining!

 

[mikerajjers]

Right, heater matrix changed! Smell is reduced and nowhere near as bad but it is still there. The old matrix didn't seem badly leaking, perhaps a tiny tiny bit, but certainly much better than I expected it to be. Now I know what it isn't The aluminium pipes from the engine bay were fine as well. I'm thinking it could be a clogged filter somewhere, what do you think? I thought it could be a set of leaking injectors, but after changing the seals they seem fine. I only get the sweet/petrol-but-not-quite-like-petrol smell when the engine is ticking over at lights or something. Definitely don't smell it in the engine bay with bonnet up at idle. It is definitely better now though. I then thought leaking exhaust pipe somewhere underneath the cabin, but I'm unsure if that would get inside.

My aircon isn't working BTW if that may be an issue. Is always on ECON and the diagnostics indicates low pressure...will need to get that regassed soon.

 

[john777w]

As I said before the condenser can harbour bacteria, look on you tube for cleaning tips