1. I don't see any oil in the coolant,
2. any other way to see whether its the headgasket?
1 is consistent with the phase-1 HG trouble
2. Cylinder compression test might
reveal the leak, but most likely will not. But you can pretty much eliminate all other possibilities.
Since the coolant is being forced out, something must be replacing it. It might be exhaust (headgasket), coolant/water vapor (might happen if part of the system is clogged or thermostat does not open), or residual air expansion.
So, here is a question: are you sure you properly refilled the radiator (see my first post above about the multi-stage procedure)? Does your heater work now? If "no" is the answer to any of the above - do it again, properly. Fill to top, idle to normal
temperature (do not let it overheat; heater ON), stop, cool, refill, repeat. Done it three times and still have air int he radiator? It's the head gasket.
Now, let's start at the point where you have full coolant system with no air This is critical! Every other test assumes that this has been done properly.
Start the car (assuming - cold), let it idle. Look at what is happening to the overflow tank. Does it start to overflow before the engine even warms up fully? And try this - with the engine warmed up (IDLE, DO NOT DRIVE!), rev the engine for a second or two. If bubbles come up almost immediately - it's the headgasket.
Here is another question - how does it overheat? Does it: A
. loose coolant and then overheats, or B
. starts to overheat immediately (heats continually from cold to hot, without much pause on "normal"), while no or little coolant has been lost yet
? If B,
you have circulation problems (waterpump, clogging), if A
- it's the headgasket.
Btw, make sure you check the radiator cap. Just buy a replacement (a few bucks in any autoparts store) to see if that solves the problem. Unlikely, but it's cheap.
Another test for head gasket - the sniff test of the air in the coolant overflow. You could do it using your noise, but it's somewhat toxic and not very reliable. The proper way is to test for CO2 and/or hydrocarbons - this can be done with a proper kit ($60-100?, not easy to find), or at most auto shops for about $40-60. Positive test means headgasket. But I'd say that the tests above should be sufficient, since you have an engine prone to exactly this kind of failure, and if all the symptoms match.... Well, at least once fixed properly, this problem should not be coming back.
Btw, what is your mileage?