2009 Q5 - coolant loss.....

[Expatscot]

After the long, drawn out delay stricken engine/refurb and rebuild (then cam installation woes listed here; cam installing tool VSE7171 - help needed (desperation) 2009 Q5 2.0TDI (vwaudiforum.co.uk))

My celebration at getting my work vehicle back on the road was premature. The car was driving beautifully - engine rebuild had worked a charm. I used the Q5 on a couple of jobs trouble free probably added a further 300-400 miles on it. Then noticed the heater was temperamental, which in turn led to noticing the coolant level was dropping (no puddle on the drive, nothing visible in engine bay).

Stopped using it for work - kept bottles of coolant with me and did some local drives.... in about 30 minutes of driving it was going through a litre of coolant.

Given what brought about the need for the engine rebuild in the first place mechanic wondered if maybe a micro-crack in the head....

But this was soon eliminated by fact the leak seemed to get worse - at least this eliminated thoughts of micro crack/head problems, it is very definitely an external leak. The cavity and bits around the oil cooler were all nicely stained pink where the coolant was coming out and evaporating. Oil cooler was thought to be the culprit and so has just been replaced. This has not fixed the issue.

- doesn't happen when at idle, has to be running hard, in use...

- no puddle under vehicle.

- it seems to be in area of the oil cooler, but isn't the oil cooler itself

Any thoughts, likely culprits come to the mind of the VAG-collective?

[Crasher]

Did you have the head skimmed?

[mickeybo]

A pressure test would not be amiss. I think your mechanic was right when he pointed to the head i have seen this problem before were the water jackets within the head leaked (cracked)

[Expatscot]

Apologies for the delay, just got back to this now....

The problem does seem to be external - well to the point that around that gap in the engine bay there was a massive spattering of pink residue from the coolant having come out and evaporated. It was all over the oil cooler, which is why it was changed out. (Problem persisted).

Mech' noticed and sent me a clip of definite visible whisps of coolant vapour coming out passed the edge of the expansion/header tank. A bit clutching at straws again but the expansion tank now replaced (though upon inspection after removal it didn't seem to have any issues).

And unsurprisingly the problem still there - further test drive: heat coming into the cabin all fine for first 20 minutes... then heat stops. After 25-30 minute drive - back home, checked coolant - header tank is empty.
So in about 25 minutes that is two litres of coolant 'gone'.

Trawling the internet has come up with: 2014 Q5 TDI losing coolant suspecting water pump | TDIClub Forums - slightly different model(s) but the problems seem very familiar.

[Richard27638]

I don't know if is related but my egr has a water cooler and they have been known to leak when the valve opens. Hopefully it isn't that and something more simple.

[Expatscot]

I don't know if is related but my egr has a water cooler and they have been known to leak when the valve opens. Hopefully it isn't that and something more simple.

That is one of the issues mentioned in the thread I linked to above.... and I am beginning to suspect it may be that... I dont know.. I am hoping the spectre of micro-crack in the head opening under pressure had been eliminated - i dont know if thats the case. There is a lot of pink splatter and stain residue from the coolant evaporating - so I would, in non mechanical logic, think that indicates an external leak.


After the last time I posted, been back to mechanic's - he let it sitting, running with a weight/someone sitting in it (whatever) point is - the revs were kept higher than just idle... they were up above 2000rpm.

No coolant was noticed - despite an hours running.

I was finally able to have time to take it for a test drive this evening. 30 minute driver emptied the head/expansion tank.

[Richard27638]

I was told egr coolant valve opens after long hot running on lift off of throttle. This dumps coolant if coolant valve in egr is gummed up and doesn't open fully. Possible.
More often seen is split in hose which opens under pressure when hot.

[Expatscot]

I was told egr coolant valve opens after long hot running on lift off of throttle. This dumps coolant if coolant valve in egr is gummed up and doesn't open fully. Possible.
More often seen is split in hose which opens under pressure when hot.

I am going to hold onto that as the next possible....

Just where the coolant is splattering and spraying is in the opening in the engine bay around the expansion tank/bottle - sitting at idle, or even 2,000 static revs for up to an hour doesn't do it... but driving conditions for 30 minutes will dump 2 litres of coolant in that time.

WhatsApp Image 2022-04-28 at 8.06.33 PM.jpgWhatsApp Image 2022-04-28 at 8.06.33 PM (1).jpg

The before and after pics - that pink/white stain is the coolant trace after it has leaked. So seems centred around the expansion/header. Going to try simply replacing the cap, maybe it has weakened over time and under pressure build up of driving is leaking it out. This car was in daily heavy use, it has done 205,000 miles - and has sat for 5-6 months with no, then very little use... stuff will be wearing out. For a few quid for a new cap worth trying before digging into EGR cooler.

[Richard27638]

Worth a try. Are the rad fans coming on at the correct temp?

[Expatscot]

Worth a try. Are the rad fans coming on at the correct temp?

Yeah, fans seem to be fine.

Finally new cap arrived.

Topped up coolant (it took about a litre).

Ran for 20 mins at idle - occasionally pressing accelerator. Minimal loss. Topped up again, engine now at operating temp.

Took for 20 minute run. Heater was rarely pushing out hot air.... only a few times. Expansion tank almost empty.

Noticed coolant pooling behind the expansion tank in some bolt recesses. And a fibre/material heatshield that goes along the rear engine bay wall, was soaked.

So it seems, when under pressure there is a release from the area of the expansion tank which is releasing air and coolant.

Question now is - what is causing the pressure build up?