Sudden Coolant loss—I don't think it's the head gasket

I know, the first thing that comes to mind is a head gasket failure, and I'm absolutely not ruling that out. Anyway, here are my symptoms:

This has happened twice, coolant levels are fine when I start my car. 10 to 20 miles down the road, the engine temperature light turns on for about 30 seconds, after which my coolant tank is dangerously low, but everything runs as normal with no loss of power, misfires, or return of the temperature light. I get back home, top off the engine coolant, and everything is normal for several thousand miles. The coolant doesn't even drop a millimeter during this time. I make it a regular habit to check my fluids. Suddenly, one day many thousand miles later, the engine temperature light comes back on after 10 to 20 miles of driving, and what do you know? The engine coolant is suddenly low again.

Here's why, to my understanding, I don't think it's the head gasket (At least I hope . . .):
1) Oil looks perfectly fine, no milky color.
2) No white steam exiting the tail pipe.
3)No loss of power and/or engine misfire
4) No lights aside from the temporary engine temperature light, which for both occasions has only lasted about 30 seconds.
5) After two occurances, I have lost a substantial ammount of coolant, if that were going into the combustion chamber or the oil, surely I'd have experienced one of the symtoms above, right?

Lastly, if it's a leak, there is no evidence of leaked on my garage floor.
What puzzles me the most is the fact that I won't lose a drop of coolant over several thousand miles, but suddenly I lose the majority of it over a 20ish minute period. My best guess is it's related to the water pump but I don't have very much information to support that with my current understanding of the issue at hand.

Any thoughts? Thank you in advance

Year: 2010
Mileage: 203,000
Because it will be asked: Yes I have cleaned the EGR system recently (also cleaned at 100,000 miles)

 

No cold-start shaking, even with temperatures near 0°F, not a single misfire code or shudder. EGR cleaning did indeed include the intake manifold. Everything runs completely normal, even during that short window when the coolant disappears.

 

Would you mind elaborating? I know there are several different solutions included in this kit. Which solution in particular are you referring to and why?

 

Dangerously low means an inch and a half or so from the bottom of the resivoir. After both occurances, it was the same ammount of cooloant lost, though I have not measured it.

 

After I see that little red engine temperature warning light, I check my coolant levels (and other fluids for that matter) after every drive. At least until I can verify that my fluid levels have not changed over 500 or so miles, after which case I check fluids after filling my gas tank.

 

I do not have Techstream, though I do have Torque Pro, and havent yet explored all its capabilities entirely. I don't suppose you'd know whether or not Torque Pro is capable of monitoring the water pump RPM? In the meantile, I'll look to see if I can find anything that looks usefull in the app.

 

A quick google search shows 'coolant leakage' and 'overheating' as indicative signs of a failed water pump. Which would make sense, however I hesitate to say that I have leakage because of the intermittant disapearace. I would expect a leak to slowly drain over time. That and the lack of residue on my garage floor. However I will look into removing the engine air filter and intake housing today to see if I can see any signs of leakage near the pump itself.

I did recently create a post looking for identification for a part near the water pump that was coverd in some black residue. I discovered this to be the oil pressure switch assembly, and assumed the residue to be oil, however I will also look more into this to see if I can determine where this is comoing from and whether or not its related.

 

I will be having it pressure-checked, thank you for the advice. I'd be hesitant to say it's as simple as a leak because this 'leak' seems to only exist for a short period of time once every x,xxx miles. I refilled the reservoir this morning, drive 109 miles today, with no drop in coolant level. However, I am absolutley not throwing the possibility of a simple leak off the table.

I almost had a stroke trying to read this, but there is no burning smell. Coolant temperatures stay between 185°F and 205°F, and when the coolant does dissapear, it does not magically return.