A few weeks ago, I had a pretty big scare when I had a big plume of smoke start coming out the car. After some quick inspection, the problem was speculated to be a missing oil cap gasket, which caused a bunch of oil to land on my exhaust manifold. Many members here speculated it might be a blown head gasket.
I decided to buy a head gasket leak checker. I found one well reviewed on Amazon
Amazon.com: UVIEW 560000 Combustion Leak Tester: Automotive
It worked really well – basically you stick this blue liquid in this contraption, plug it into the radiator cap, rev the engine a bunch of times and then using a bulb, suck up air from the radiator compartment – if you see the liquid turn yellow – you know some exhaust is getting into the radiator compartment, and most likely a head gasket leak.
The whole thing takes about 10 minutes.
Good news – no yellow liquid.