Q5 Q5 coolant loss.... (2009, 2.0 TDI).

[SecretSquirrel]

My Q5 is my work beast - I cover about 3500-4000 miles month and is had never skipped a beat - got serviced 4-5 times a year .... loved it.

Late 2021 I took my eye off the ball due to family tragedy and cambelt went - as I had just had a new clutch & DMF fitted, decided to repair. That became a delay stricken protracted job (some of which detailed at another forum: https://www.vwaudiforum.co.uk/forum...7171-help-needed-(desperation)-2009-Q5-2-0TDI)

Anyway - after refurbing, and renewing parts and 5 month delay got the Q5 back 10 days or so ago. It was driving beautifully, back to using it for work, put a further 300-400 miles on it. Noticed the heating was being temperamental, which led to noticing coolant loss. No puddle on drive and it wasn't showing loss at idle. But when driven and revved - coolant was def going somewhere, losing about a litre in 30 mins of driving once up at temp.

Initially it was thought possibly a micro-crack in the head as no sign could be seen of leak.... but the leak then got worse, pink stains around oil cooler area where the coolant was coming out and evaporating.

So, maybe a bit presumptively, the oil cooler was replaced and assumed this would fix issue - seems it wasn't the oil cooler.

Any likely culprits that spring to mind? The vehicle has done 205,000 miles so parts can be expected to wear, but with new clutch/DMF and now a complete engine refurb/rebuild I was hoping for couple more years of work beast use, for all its old it is in lovely condition and a pleasure to drive.

- only happens when hot and under pressure (being revved/driven).
-leak seems to show in area of oil cooler, that gap and the area around it stained pink.
- isn't the oil cooler itself which has just been replaced.

Whilst I am relieved it is not crack within the head and is an external leak, each delay and new problem means I am hammering miles on my other car which isnt designed for work use.

 

[Garrett 69]

Stat housing?

 

[SecretSquirrel]

Only just got back to this now.
So - after the engine rebuild (which went very well and it drives great) had this coolant loss.
Oil cooler was - prematurely - deemed to be the culprit and switched. Problem persisted.
Then there was this little video of coolant escaping as vapour .... (cant see how to post vid clip)... which seemed to be coming from the expansion tank.

.... so the expansion tank was replaced.

Taken it for yet another test drive. First twenty minutes drives fine, heat coming through to cabin. Then the heat stops coming in.
After 25-30 minute drive it has emptied the expansion/header tank.

I know these sorts of problems can be difficult to trace.... but its ******* through 2 litres of coolant in a 20 minute drive. I am still just tankful its external but is becoming a real pain in the ***.

 

[Garrett 69]

Maybe a coolant hose with a pinhole that opens up as the hose expands. In these cases I usually find that the hole is either inside or outside of a bend in the pipe or around the clamp area.

Other than that, possibly a rigid pipe fitting not mating correctly.

 

[SecretSquirrel]

Maybe a coolant hose with a pinhole that opens up as the hose expands. In these cases I usually find that the hole is either inside or outside of a bend in the pipe or around the clamp area.

Other than that, possibly a rigid pipe fitting not mating correctly.

Cheers, I am away for couple of days so mechanic going to take it again at some point and get it up on ramp if need be with someone revving it...

We still seem happy to have moved passed micro-crack in the head, given the pink splattering around the engine this seems external for sure... have found this thread elsewhere which may hold a clue (it wont be the water pump that just been replaced, as has the oil cooler).

2014 Q5 TDI losing coolant suspecting water pump

We purchased our Q5 TDI a couple of months ago. The other day, I could smell coolant but no puddle underneath and no visible sign of a leak, but there's a significant loss of coolant from the reservoir. I borrowed a pressure tester today and the system had no problem holding 15 psi and no...

forums.tdiclub.com

 

[Garrett 69]

I'm surprised there's been no-one else offering their thoughts on this

 

[SecretSquirrel]

And the latest update.... I have been on a busy schedule and not had time to liaise with mechanic...

I have seen links in thread on differen forum about a leak from the EGR cooler which, if it happens, is well hidden and hard to trace... I dont know..
I am hoping the spectre of micro-crack in the head opening under pressure had been eliminated - i don't know if that's 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.

 

[SecretSquirrel]

Trying new cap - for sake of a few quid worth eliminating the obvious.

Finally new cap arrived.

So, today, 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 after this 20 minute drive.

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?