Quick question STOP coolant message

Proud owner of a 250k 2006 tdi - 3rd TDI I’ve had but wanted take on this. The individual I bought this from has records since day 1 and took it in to VW dealer at 270k because he said he was having to put in coolant. The VW notes state they did a flush on vehicle and changed the tank because of a leak? Anywho I’m getting the message now pop hood and the coolant looks close to the minimum line but a little above it. If I opened hood and turn cap on coolant box I get a little hiss and it seems the coolant rises a bit. I crank car and error goes away? Is this simply a case of topping this off or do I have a slow leak still possibly?

Sounds like a slow leak. I have to add a couple of ounces every six months to my '09 for this reason. Actually, I added 4oz. today (2oz. Pentofront + 2oz. distilled water) after I finished changing my oil.

MP517PRCT said:

Sounds like a slow leak. I have to add a couple of ounces every six months to my '09 for this reason. Actually, I added 4oz. today (2oz. Pentofront + 2oz. distilled water) after I finished changing my oil.

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Is the only one the g12 stuff for a 2006? And the stuff I have in it is red but can I switch to Pento? Is it g12 as well? Okay to mix colors if reds in now and Pento is different?

Check the coolant flange, its gasket is known to fail and cause slow leaks:
https://www.idparts.com/coolant-flange-for-cylinder-head-seal-a5-brm-p-5526.html

I had a slow leak in one of the EGR cooler hoses that only manifested when I was towing a 6x10 enclosed trailer. The giveaway was the softness of the leaking hose- there was no readily apparent spray or drip.