Elusive coolant leak

[Nudist]

I am having some difficulty in resolving a coolant leak in my M7 golf diesel. It all started three or four weeks ago when the coolant level indicator came on early one morning as I was about to leave home. I drove the car for a few minutes then the indicator symbol disappeared. I thought nothing of it.
The indicator came on a second time a few days later As I was driving the car around. I then noticed The coolant level was below the level of the little metal sensors fingers inside the coolant reservoir.
To cut a long story short, I booked it in to my repairer And they immediately pressure tested the system and for half an hour to an hour and the pressure held. And they couldn’t locate any obvious leaks underneath the vehicle. Subsequently they have replaced the coolant and I have made one trip Canberra and Sydney return. That was three weeks ago and I haven’t driven the car since. However I did notice that when I was in Sydney the coolant level light came on as I was about to return to Canberra immediately stopped and unscrewed the On the reservoir and the level was still good. The indicator for the return trip and the temperature gauge was reading as normal.

I was planning to make another trip to Sydney on Saturday and went out to the car and inspect the level of the coolant and low and behold the level has dropped and I’ve had add an extra litre of water to it to bring it back up to the correct level. So given all of the above information I’m a bit flummoxed as to what the problem is.

Has anybody in the group experienced something similar with their golf and if so how did they eventually locate and fix the problem?
The leak appears to be minor at this stage so I am planning to drive the car but make sure I carry some water with me to top up the reservoir

[PEM]

Hey Nudist,

I had a similar slow leak in my Mk7 Alltrack 1.8TSI. Turned out a piece of gravel had wedged against the radiator and wore a hole, possibly due to subtle vibration? My mechanic found it, patched the radiator, and so far it's held with no need to top up.

[blaast]

If there are no external leaks, it might be the water pump if these are internal.
If the water pump is internal, they can leak into the engine.
Check to see if your oil level is increasing or if there is a milkiness colour to the oil under the oil cap or dip stick.
If so, it is likely to be the water pump.

My T5 2.5TDi has just had this happen to it...

[gregozedobe]

There are only a limited number of places where coolant can go:

1 External leak (most often from the thermostat/water pump housing on Golfs), look (carefully) for dried residue around engine bay

2 Internal into the engine oil (as blaast says, look for increase in oil levels and milky/mayonnaise appearance)

3 Internal into the exhaust (sometimes via combustion chamber), can show as excessive steam/moisture in exhaust gases (can use a "sniffer" to detect coolant in exhaust gases)

Note that these Golf engines are known for having trapped air in the system whenever the cooling system has been disturbed (and even from new). When the trapped air finally works its way through the coolant systems the coolant level will lower (mine did from new). As you were previously having coolant level issues before the coolant was replaced I think you are right to be cautious. Keep a close eye on the coolant level to see if it is consistently dropping, if it is then you need to find out why and fix it.

To get an accurate coolant level always check when the engine is totally cold. Checking when the engine is hot can be misleading.

[Nudist]

Thanks Apologies for the very late reply. I don’t check this forum very often

[gregozedobe]

Thanks

Did you get a resolution to this problem ? And if so, what was the issue and what was the fix ?

[Nudist]

I haven’t driven the car for the past five months because of the pandemic and then I was driving it less for the previous 12 months because we have a new Kona EV and we’ve been using that in preference to the golf which I reserve for interstate travel. I take THE Golf back to the mechanic tomorrow and I’ll ask him to do yet another pressure test but I will ask him to look into these suggestions that you made.
It is quite annoying because it seems to be a leak that only occurs after I drive the vehicle It doesn’t seem to leak it’s just sitting in the carport. Things are coming to ahead in the next few weeks when I drive down to Melbourne so I don’t want any dramas that are going to hold me up. Ps I have found posting this comment an ordeal. I attempted to post it from on my iPad and then my Mac and now I’m trying on my iPhone. In the first two devices there was the long delay between typing comments and them appearing on my screen Then I hit the post button and saw the message saying it was processing and then nothing happened. This explains why I ended up posting the same comment three times. Apologies for the confusion. I will keep you posted about the results of the next service fingers crossed.

[gregozedobe]

It is quite annoying because it seems to be a leak that only occurs after I drive the vehicle It doesn’t seem to leak it’s just sitting in the carport.

If it is leaking the coolant must be going somewhere, so maybe a snake camera might show up signs of dried coolant somewhere in the engine bay. If it tests OK when static then the cause of the leak might be something like a pin hole leak in a hose that only opens up when the hose gets hot, or a connnection that only leaks when the engine is moving, or something similar.

[Nudist]

I am closing this thread because I have located the problem which was opened another line of enquiry about the suitability of plastic part on the golf coolant system.

Plastic housings and connector in a Golf 110 diesel