Occassional loss of coolant .... pressure relief??

[Andy Clegg]

Hi, I've got a Seat Leon 1.8TDI, and have had a few instances where it has lost coolant (coolant level warning light, etc). I have been monitoring coolant level closely, and after most journeys it does not move at all, including where I have driven hard to get engine temp high, but no loss of coolant and level just stays same (once cooled). But on a short motorway journey (40miles) it did loose about 100-150ml coolant in that one journey. There was a bit of coolant in the places marked in yellow circles in photo. I've never seen any coolant actually leaking / spraying. Does the coolant expansion tank have a pressure relief to vent coolant when pressure too high ? Does where where I saw the coolant match where any vented coolant might end up?

BTW - after the first time of loosing coolant, I saw the posts here about the silica bag in the coolant tank and it looked like the one in mine was burst, so the expansion tank was changed as first measure - but it has not fixed the occassional loss of coolant. I suspect the bits of silica have made a small blockage somewhere and that the coolant system pressure is going up higher than it should, and giving the occassional venting of coolant. But the cabin heating seems to be normal, which seems to be common problem with a burst bag, and the car warms up just as normal. Does the expansion tank cap do anything, as that wasn't changed?

Thanks,
Andy

 

[SuperV8]

These are symptoms of a blocked heater matrix.
The heater matrix can get blocked from leaking silicate, left over casting sand or just general detritus in the cooling system.
The matrix is on a micro coolant circuit - shared with the EGR cooler so if this circuit if blocked you can get local boiling of the coolant after a DPF regen, which over pressurises the coolant which escapes out the pressure relief cap.
Probably need a cooling system flush - and a new heater matrix. Do the flush BEFORE fitting your new matrix!
New matrix is fairly simple job - don't need to take the dash out as some dealers try and charge a lot of labour.
Have a search on here for heater matrix - very common.

 

[Andy Clegg]

@SuperV8 - thanks, your comment that the boiling off can be related to when a DPF regen happens is very useful, as may explain why I didn't get any loss of coolant in my attempts to get the engine temp high with some "hard" driving around, and that it seems to happen during motorway journeys. The cabin heater is working, i.e. giving out hot air, but good that you confirm what I have read in many posts on here that it could be a blockage somewhere.

Does where I have seen the bits of coolant in engine bay match with venting due to high pressue ? I've tried to figure out where it vents from, but I can't see anything obvious or have read any clear description.

BTW - my oil temp seems to be a bit higher than is normal, 100degC for normal driving, 110degC for harder driving or when weather is hot. But there are so many variables that it could be anything, something or nothing.

 

[SuperV8]

The pressure relief valve is in the expansion tank cap.

As the matrix gets more blocked - you may find a difference in temperature between left and right vents.

My drivers vents where cooler than the passenger vents when on high heat.

 

[RUM4MO]

You asked where exactly does the discharged coolant escape from - if you look at your picture, at the LHS of your series of yellow dashes, you should be able to make out a raised section running down the side of the header tank, it is via this flattened tube that the coolant's escape route is which, if memory serves me, terminates at the welded join area of the header tank - that flattened tube's open end should be down there.

 

[Andy Clegg]

Thanks guys - very helpful. Whilst my local garage (not a SEAT dealer) is helpful - it is good to be able to give them a steer on something like this where the problem is more intermittent or subtle. Great to have such a forum.

 

[Ivicapivo]

Hi
Can you tell us if you solve the problem with coolant losing, I have the same problem when the DPF regen start...thanks

 

[Andy Clegg]

Hi - I've only just had a coolant flush done, and haven't driven the car long enough to know if it has stopped the occassional loss of coolant I was getting. For me it seemed to loose coolant on a longer motorway journeys (which are infrequent), but it has also done it on shorter journeys. I've got a long journey next weekend, so I'll post after that.

 

[mcspook]

Hello,
I have a 1.8tsi and also losing some times coolant. I had a leak from the water pump and had it replaced, but this time I don't have any leaks and have some red residue from the coolant on the rubber that seals with the bonnet after very hot days. After how long do you see a change on the water level?

Sent from my Pixel 5 using Tapatalk

 

[Andy Clegg]

My coolant level can stay perfectly constant (once everything cooled) for many short drives, so it is not a continuous slow loss of coolant. If it does loose coolant after a drive (often a long motorway drive, but not always) and I get the coolant splashes at the front bulkhead / bonnet, it will have lost about 200-300ml (how much new coolant I add to top up to the level it was at originally).

 

[lhunter664]

Hi Andy, I’m having the same issues that you have stated here. Did the coolant flush solve your issue or did you need to get the heater matrix replaced?

 

[Andy Clegg]

It's still loosing coolant, but things have changed .... gotten worse!!

After the coolant flush, it actually started loosing coolant much faster!! Before the coolant warning light would only come on during on long motorway journeys - and even then not every motorway journey. After the flush (and change of expansion tank cap) a drive of just 10 miles the level in the expansion tank drops by about 1cm with coolant around the outside tank, so after just three such journeys the coolant warning light comes on. So it has gone from something that was just an inconvenience to a car that is barely usable.

Its been pressure tested several times, and not loosing anything. Judging by what people have said - the next thing may be the heater matrix changed - but I am getting heat in the cabin from all the vents, so it isn't totall blocked. I'll update this thread if I get some progress.