What do your exhaust tips look like? Have you pulled any plugs and looked at them?
: >> Doesn't leak when the car's idling or standing still, even after 1/2 : >> hour or more. Revving it up all the while - no leaks. No puddles : >> after it's parked, nothing wet underneath. It's gotta be happening : >> only while driving, but what the heck could be the source? Water : >> pump's dry underneath, no signs of leaks or wetness anywhere near the : >> radiator. Oil's just fine, so no head gasket problems. : >>
: >> Any ideas? : >
: > It could be a number of things. As BY mentioned, it might be a : > leaking head gasket. This could show as steam exiting the exhaust but : > sometimes that isn't the case. A mechanic can check for the presence : > of hydrocarbons in your coolant and tell if combustion gases are : > leaking through the head gasket. This won't tell if the leak is : > one-way (i.e. if the coolant is leaking into the chamber). Other : > than this it would have to be leaking somewhere, somehow. It might be : > a slow leak that happens in a place that won't leave a puddle. Also, : > you might check the heater core but this usually is obvious from the : > smell of coolant and/or a steamed up windshield. My Explorer had a : > leak I couldn't find and it turned out to be a crack in a plastic : > distribution piece next to the firewall. Only after it broke : > completely did I find it. Good luck, finding a slow coolant leak can : > be a real PITA. : : Yah, that's what it's turning out to be. Can't find a damn thing wrong : with it, and it runs beautifully. No telltale noise, smoke, water, : anything. As soon as my son's done with school I'll take it in and have : them check it out. In the meantime, we'll just keep filling it up every : weekend...