Coolant disappearing but no leak on NA IDI

[FrankenDiesel]

I have background in engine mechanicals and whatnot. On my IDI, i notice that the low coolant light comes on quickly even after topping off. Usually, its good for a while, then it gets so low that I notice the engine starts to run hot and such. Anyways, I do not really notice water under the car or while idling.

I do see usually a little green under the head flange with the ECT sensor. However, under idle and reving I do not see any leaks. I wanted to pressurize the system, but VWs have those funky coolant resevoirs so I am not sure where to even get a tester kit, nor do I wanna shell out for a one time use tool.

Im just looking for basic ideas. I am going to be replacing all the hoses, inspecting the metal coolant pipe, interior doesnt seem to have a leaky core, and basically go over visually. A guy online stated that these often have head gasket issues, and I was curious about that since my last idi did seem to drink coolant too. Is this normal, or do these cars have gasket/possible cracked head/block issues?

The car runs fine, no power loss issues/smoking. This is just solely based on a coolant consumption complaint.

[vanbcguy]

They CAN be bad about head gaskets, but usually they do well as long as they aren't overheated. Once they get overheated they often warp their heads making it hard to get a gasket to seal.

Not sure what year you have here but a very common place for them to get intermittent coolant leaks is the plastic flanges attaching the hoses to the head. They were metal on the older engines though those ones tend to corrode. The plastic ones will last about a decade just fine but past that they tend to warp causing occasional small losses of coolant when the car is hot but no big puddles. 

If you do have the plastic flanges it's worth replacing them, shouldn't cost you more than $15 for both the head ones.  The thermostat housing suffers from the same thing though that's a little bit more involved to replace.

[burn_your_money]

You can pressure test the system by T-ing into the small line going to the coolant overflow bottle.

How quickly does the cooling system pressurize from a stone cold engine? I'd run it from cold for 30 seconds to 1 min, then open the cap and see if it's pressurized. If it is, it's probably the headgasket. You can sometimes see the air bubbles coming into the coolant bottle with the engine running as well. Again, that's a headgasket.

Do your vents smell sweet? You could have a small leak in your heater core.