C8 slow coolant leak

[pointysticks]

Hello FCF people.

I got here 2006 C8 diesel (2L, 5sp manual), that's started disappearing coolant and beeping at me.
Several refills later (about 2 weeks apart) i need to sort this out.
Everyone and their grandma screams "head gasket", but i found that some header tank connecting parts are cracking on these cars and leaking slowly.
There is no obvious leak, no spots on driveway etc. I hope that this is something that's NOT head gasket.
Car is driving fine, no abnormal white/black smoke out the back. Dipstick is clean, no mayo in oil.

I'm not handy with engines/mechanics, but is there a way to check for actual leaks before i tell my mechanic off for suggesting head gasket failure again?

Any insight and advice is appreciated.

[gwest]

I am not familiar with these diesel engines but they may well use similar O ring sealing strategies to the petrol engines, which inevitably fail. Things light thermostats, water pumps, water pump plastic coolant pipe and oil coolers come to mind. The leaks are not dramatic and can easily be overlooked. There are quite a few cooling system hoses with click on connections that have O rings, as does the expansion tank feeder and drain lines. And that is apart from expansion tanks failing. So you are right, there is no reason to suspect a head gasket early in the diagnosis.

[white exec]

Hi, and welcome.

A coolant leak usually shows up as a white/pink/blue/green powdery deposit where the leak is.
If no leak is visible, then it could be HG, and the coolant is being drawn into one of the cylinders, and burnt off.
With conventional glycol coolant, this usually shows up as white 'steam' (actually white smoke) coming from the exhaust, made more so by using heavy throttle, and the vapour produced smelling slightly sweet (the glycol, again).

Another possibility is the header tank is being over-filled, and the excess just thrown out by repeated expansions.
Why would it be over-filled? One possibility here is that the "coolant low level" warning is coming on prematurely (i.e. at the wrong level) because the level sensor probes (usually two metal prongs, looking for conductive coolant), have become corroded, or even just dirty. A bit of oil in the coolant can coat the probes (with non-conducting oil), and make them mis-read the level. So, worth checking the level sensor.

One way of telling probe/level problems from continuing coolant loss is to temporarily disregard the level warning, but carefully regularly check the physical level of the coolant in the tank, each morning while engine is cold, and see whether it continues to drop each day. If it does, you have coolant loss via a leak, or HG, or...

...One more thing:
If coolant has been recently replaced, and the cooling system was not thoroughly bled, it is possible that there could be an air-lock (trapped air) in the head, and that could result in a hot spot, enough to cause localised boiling. This is enough to throw some coolant out.
If the header tank has an over-flow spout (usually near the pressure cap), connect it into a small bottle/container, so you can monitor what quantities get thrown out.

[pointysticks]

Well, just this morning i topped up the pink stuff as tank was below MIN. Will have to inspect engine for white deposits.
Cant detect any sweet smell or white exhaust when at motorway speeds (2.5k+ rpm) or accellerating from stationary.