Easy stuff first, but are these likely related?

[idotavant]

I have tried my best to do research before posting. I will be doing/checking the easy stuff first, but thanks for any help on my tedious, amateur, b6 problem post.

I know about many heating and coolant system issues on the car, but I am having some that could be related to one issue or multiple issues at the same time. Symptoms include:

1. No heat. High speeds cooler. A little warmer low speed and higher revs.

2. Gurgling overflow tank. Can't be sure if it's overheating, temp gauge is in the middle, and supposedly inaccurate. Seemed to want to boil over when I got the tank lid almost all the way open, as some coolant puked out, but I closed it.

3. Smelled coolant here and there, coming from under the hood/wheel well. Evidence of coolant leakage under the expansion tank. Lid doesn't seem real tight. Tank has a small (1") crack, but doesn't appear to be leaking from the crack at all.

Air purging and checking that the fan comes on are first on my list. Looking to eliminate easiest+most likely.

3.0 tip b6 avant. 02 178kmi. Will be tackling this after the starter and axle get replaced. Yikes.

[diagnosticator]

Does the exhaust smell like it has coolant in it, particularly just after cold starts? The symptoms you described are often associated with coolant leaks, or a failed head gasket. With coolant leaks, when the cooling system reaches ambient temps after driving the car, the pressure in the cooling system becomes slightly negative, or less than the outside ambient air pressure. If there are cooling system leaks, air is pulled into the cooling system until the internal and outside air pressure are equalized. Then more coolant can leak out of the system.

Leaks will also cause the coolant level in the expansion tank to decrease at variable rates depending on coolant loss. What is the status of the coolant level in your system, steady or loosing coolant?

Pull the spark plugs and examine the firing tips for unusual discoloration from coolant leaking into any of the cylinders.

Air admitted to the cooling system will collect in the heater core, preventing coolant flow through the heater core. Excessive air trapped in the cooling system will also compromise cooling effectiveness provoking development of hot spots that will result with localized boiling in the cooling jackets. When the expansion tank cap is loosened with the coolant still hot, resulting pressure reduction in the cooling system allows flash boiling at the hot spots and steam production that will force coolant out of the open expansion tank. With the tank cap loosened or removed, reduced cooling system pressure allows trapped air to expand a lot that will also force coolant out of the expansion tank. Trapped air will also cause the coolant pump to cavitate reducing coolant flow in the engine and heater core, compounding the severity of the several malfunctions and effects of low coolant level and engine localized overheating.

If the temperature sensors are not submerged in liquid coolant, the sensed temperature will not be accurate.

[idotavant]

Yep. That all makes sense. I'm not loosing much coolant if any. Evidence of leakage is under the expansion tank. That could be leaking from a breach or puking from overheating right?

[idotavant]

So, I will try to make sure the fans come on and look for indications of flow/pressure from the water pump. Sniff the exhaust for coolant on cold start, check plugs for discoloration. I can also let the car warm up with the reservoir lid loose, then close it for a few and open it again in an attempt to purge. Can also attempt to bleed air out in a few other spots. Look for leaks visually. Check the lines in various locales for heat. Gauge moves to middle and stays there; does that mean it is probably not the t-stat? I will be doing full timing belt service in a couple months, so more involved trouble shooting can occur then.

Trying to ascertain whether the car is actually overheating. Seems unlikely since it is 18F when this happened with not too much idling. If not over heating, then air is stuck in the system and/or getting into the system. I drove the car 300 miles and lost no coolant that I could see, but it was fairly cold and 70mph. I have no idea of the cars history. It appears to be a very solid, clean, well-driving basket case. In the three days I have been driving it, I smell wiffs of coolant outside the car. Only saw it gurgle in the tank once when it had idled a bit, but it was still very cold out. Low investment troubleshooting first. Looking for all the easy tests.