Hi All,

My 2.0tdi 150 manual (80k miles) has began to loose coolant at a rate if 500ml every one or two weeks. I had the coolant system flushed under skoda warranty about 6 years ago and the expansion tank swapped for one without the silica bag (as the original had split leading to no warm air).

I thought at first it may be a water pump but no other signs such as water under the car etc with the only symptoms being the low coolant light coming on, coolant temp staying in the middle..... but .... I've also noticed white staining around the filler cap which is getting worse and the cap seems supringly easy to unscrew. In the past it was always very stiff but even when warm it it easy to unscrew with no hiss anymore.

I'm beginning to think the issue is a dodgy filler cap not sealing anymore casing the coolant to boil off leaving the white residue .

Does that make sense ????

Thanks

Sounds like a good plan to replace the cap first. Make sure the replacement is genuine OEM quality.

Thanks Warrior, I'll get one from my local dealer so will br a VAG genuine part to make sure the pressure relief valve has the right working pressure 👍

4 hours ago, 3rdoctavia said:

Thanks Warrior, I'll get one from my local dealer so will br a VAG genuine part to make sure the pressure relief valve has the right working pressure 👍

also carefully check the threaded neck of the expansion tank when you clean it up.

I Went to the dealership today and got a genuine cap for the tank which is now in place.

It's a slightly different design on the top compared to the original but it screwed in the same. The guy on thr parts desk said they had changed them a bit but it's the correct part.

 

I managed to unscrew the old cap with very little hiss and no steam suggesting there was only a small amount of pressure In  the system despite the engine being warm  I'd expect a sealed sytem under pressure would have spit and spluttered when the pressure was released allowing the fluid to boil but there was none of that.

 

If this works ill sort the old tank too.

 

For reference the cap was £22 and a tank is £45.

 

Cheers

Note that there are plenty of good quality, OEM replacement expansion tanks available for less than half that price.

Thanks Warrior, for the tank I'll get one from Eurocar parts .

 

They do a Mahle one for about £25, and with no moving parts I'm happy to use a copy part 👍

 

I've noticed my radiator fans being on more too when I've parked up which I presumed was due to a regen happening. Although I suppose it could also be due to the coolant system working hard if it wasn't under sufficient pressure due to a faulty cap ( yet temp on the dial was lways ok).  🤔

Keep an eye on things. Could also be a leaking egr cooler or leaky charge cooler causing things. 

Hey

On 21/10/2024 at 11:19, 3rdoctavia said:

Hi All,

My 2.0tdi 150 manual (80k miles) has began to loose coolant at a rate if 500ml every one or two weeks. I had the coolant system flushed under skoda warranty about 6 years ago and the expansion tank swapped for one without the silica bag (as the original had split leading to no warm air).

I thought at first it may be a water pump but no other signs such as water under the car etc with the only symptoms being the low coolant light coming on, coolant temp staying in the middle..... but .... I've also noticed white staining around the filler cap which is getting worse and the cap seems supringly easy to unscrew. In the past it was always very stiff but even when warm it it easy to unscrew with no hiss anymore.

I'm beginning to think the issue is a dodgy filler cap not sealing anymore casing the coolant to boil off leaving the white residue .

Does that make sense ????

Thanks

Did this solve your issue? May be having a similar problem

5 minutes ago, maxhill1996 said:

Hey

Did this solve your issue? May be having a similar problem

Hi,

I took it into my local garage who had a look and diagnosed a leaking water pump. So after booking it in and getting it changed the guy showed me the wear on the old one which seemed to have some sort of plastic part that was clearly worn ( i wish id took a photo). At the same time he swapped the header tank and re-used the new cap id already purchased. To be honest the cap fitted much better on the new tank and was less stiff.

The new pump and tank sorted the problem 👍

Edited 14 February14 Feb by 3rdoctavia

23 minutes ago, 3rdoctavia said:

Hi,

I took it into my local garage who had a look and diagnosed a leaking water pump. So after booking it in and getting it changed the guy showed me the wear on the old one which seemed to have some sort of plastic part that was clearly worn ( i wish id took a photo). At the same time he swapped the header tank and re-used the new cap id already purchased. To be honest the cap fitted much better on the new tank and was less stiff.

The new pump and tank sorted the problem 👍

Ah ok! Having a mystery leak myself and local suggested either head gasket or egr cooler, so was hoping it was an easier fix. Monitoring atm, but will mention this too! May i ask roughly how much it set you back for the repairs please?

19 minutes ago, maxhill1996 said:

Ah ok! Having a mystery leak myself and local suggested either head gasket or egr cooler, so was hoping it was an easier fix. Monitoring atm, but will mention this too! May i ask roughly how much it set you back for the repairs please?

I had it done in Nov 2024 and got the timing belt changed at the same time. Ive just looked at the invoice and the total including labour and vat was £460 for pump, timing belt, fitting kit, and coolant tank.

I have an Octavia scout which has the protective under tray fitted and the guy said when he took that off there was signs of it having caught some drips. With the tray being in place nothing was showing on the ground.

Cheers

Ps I think water pump leaks are common on the 2.0tdi I believe, so that would be one of the things Id suggest.

Edited 14 February14 Feb by 3rdoctavia

25 minutes ago, 3rdoctavia said:

I had it done in Nov 2024 and got the timing belt changed at the same time. Ive just looked at the invoice and the total including labour and vat was £460 for pump, timing belt, fitting kit, and coolant tank.

I have an Octavia scout which has the protective under tray fitted and the guy said when he took that off there was signs of it having caught some drips. With the tray being in place nothing was showing on the ground.

Cheers

Ps I think water pump leaks are common on the 2.0tdi I believe, so that would be one of the things Id suggest.

Fab, thanks for checking! That's not too sad actually, obviously will have gone up, but still was expecting a lot more. Use a fantastic local pop and son indie garage who we've a good relation with so hopefully won't be horrendous as expecting a timing belt change soon anyway. Got a 2.0 diesel 4x4 so also have the under cover I think and liable to leak, so hopefully this helps troubleshoot! Clutch may be on the way out, due a timing belt change soon and with this on top seeming a likely good chunk of cash was starting to weigh up keeping her or not. 😅 Hopefully will get lucky and kill two birds with the one stone.

Cheers

If theres an expansion pipe from tank put a plastic bottle on end and run car. If theres any coolant coming out you will collect it and see how much and if your losing it from there.

Alasdair

Have you checked the heater matrix? I had an issue with intermittent loss of coolant with my 2.0l TDI and it was due to the heater matrix being clogged up with the contents of the ruptured silica bag that was in the cooling system (common issue).

The coolant loss is due to the dpf being on the same cooling circuit as the heater matrix. With the restricted flow, when the dpf was regenerating (i.e. v. hot) the coolant was boiling, over pressurising the system and coolant was escaping out the tank. As it was only happening when the dpf was regenerating it was hard to replicate at a garage.

A new heater matrix is £40-60 and easy to fit (via passenger footwell), there are videos on YouTube.

Stuart

51 minutes ago, Stuart56 said:

Have you checked the heater matrix? I had an issue with intermittent loss of coolant with my 2.0l TDI and it was due to the heater matrix being clogged up with the contents of the ruptured silica bag that was in the cooling system (common issue).

The coolant loss is due to the dpf being on the same cooling circuit as the heater matrix. With the restricted flow, when the dpf was regenerating (i.e. v. hot) the coolant was boiling, over pressurising the system and coolant was escaping out the tank. As it was only happening when the dpf was regenerating it was hard to replicate at a garage.

A new heater matrix is £40-60 and easy to fit (via passenger footwell), there are videos on YouTube.

Stuart

Thanks for the reply Stuart! Yes it was actually a clogged heater matrix that started all this, lost heating on one side etc... got that replaced and then noticed the coolant loss (although probably ongoing before. But still slowly falling since getting that sorted a month ago!

Might be worth checking new matrix as the coolant loss was noticeable after change if you can in case its leaking from connections. If its doing it when hot then any coolant may be evaporated before you notice any leaks. at 500ml per two weeks its around 35ml per day.

Alasdair

I was losing about that amount from the pump leak in the end so you have a few things to consider. The problem is that with a warm engine everything drys before making itself known other than a bit of staining that can be seem after a while.

Yeah, suspect it was ongoing before the matrix clogged, but may have caused it and now leakage is somewhere else. Could be so many things, head gasket, egr cooler, water pump. Nothing fun, or likely cheap! 😅

On 14/02/2026 at 21:41, 3rdoctavia said:

I had it done in Nov 2024 and got the timing belt changed at the same time. Ive just looked at the invoice and the total including labour and vat was £460 for pump, timing belt, fitting kit, and coolant tank.

I have an Octavia scout which has the protective under tray fitted and the guy said when he took that off there was signs of it having caught some drips. With the tray being in place nothing was showing on the ground.

Cheers

Ps I think water pump leaks are common on the 2.0tdi I believe, so that would be one of the things Id suggest.

Hey I suggested this to the garage when I dropped it off and they said they found some evidence of residue and leakage, so hoping we've got it! Excellent shout!!

Following up on the above, needed a small amount of coolant top up after the wor, but othewise has been holding steady! Great shout @3rdoctavia !

3 hours ago, maxhill1996 said:

Following up on the above, needed a small amount of coolant top up after the wor, but othewise has been holding steady! Great shout @3rdoctavia !

Great, maybe an air bubble in the system meant you needed to top up after the work so it sounds like its sorted. Thanks for feeding back on your success 👍

Glad you found the problem an its sorted. Coolant loss can be a nightmare to find.

Alasdair