Head Gasket issue?

I recently bought a 2000 Explorer with the 4.0 OHV engine. The other day I started it and was getting a lot of white smoke out the exhaust. I think I have a bad head gasket or cracked head, but before I tear into it I want to make sure it might not be something more simple.
As part of my maintenance on this, I recently replaced the thermostat, radiator cap and hoses, so I am not sure if the antifreeze I needed to add was related to that or this other issue. I don't want to run it again as I understand that the antifreeze will ruin the catalytic converter.
Is there anything else it might be? Any help would be appreciated.
Thanks!

White smoke in cold weather is not unusual, especially for a while after start up. If the smoke is white and not blue or black, it would be either from coolant getting in the combustion chamber or the cold weather. When you pull the dipstick out does the oil look like it may have coolant in it? A better question, do you see any other vehicles around there with white smoke coming out the exhaust?

Do a compression test to start, see if you have any low psi clyinders. If you find any low compression clyinders do a leak down test with air pressure.

In addition to the tests mentioned about, for around $25 you can pick up a Combustion Gas Detection Kit that will tell you if there is CO in the cooling system which would be indicative of combustion gases making it in to the cooling system. The less expensive kits rely on an external source of vacuum for the test so you either need to also have a hand vacuum pump or connect to manifold vacuum and run the engine (which I know you're trying to avoid).

Mechhound is probably right though and what you are seeing is the condensation burning off.

-Rod

Thanks to everyone for their help and suggestions. I will try the compression test.
Regarding the exhaust. Since it is cold here, I always have some white smoke - condensation - but this seemed to be much more than the usual. Also, something I thought of later is that I had noticed the last few times I started it, it would run rough for just a minute or two. I am thinking that it might have been some fluid getting into a cylinder, but not sure.

Also, something I thought of later is that I had noticed the last few times I started it, it would run rough for just a minute or two. I am thinking that it might have been some fluid getting into a cylinder, but not sure.

You could have a vacuum leak that opens up when the engine is cold and either closes, or the PCM compensates for, as the engine warms. Such a vacuum leak could explain the roughness and could also (maybe) contribute to what seems to be more white exhaust than expected.

Try the compression check, keep an eye on your coolant level, and if you're still concerned you have a head gasket issue, try the combustion gas detector. Vacuum leaks due to intake manifold gaskets or cracked manifolds seem far more common on these engines though than head gasket issues.

-Rod