I haven't driven the 4Runner for 2 weeks so this weekend I decided to give it a bit of exercise and figured I'd do a quick fluids check first. It turns out the radiator overflow tank is bone dry, and looking in the radiator cap I didn't see any fluid. Obviously this is not a great thing to see. The truck also been loosing some oil recently, which I think is due to a leaky valve cover gasket.

The oil on the dipstick looks normal and not milky, so I'm really hoping this is not something dumb like a blown head gasket (truck only has 110k miles), and instead suspect a coolant leak somewhere such as the rear heater lines. So, the plan is to remove the skid plates, put some water in, bring things up to temperature and look for leaks. As a precaution I'll also pull a couple spark plugs and look for any signs that coolant is getting into the combustion chambers. Any other suggestions on how to debug this?

- Matt