I've noticed a coolant spot under my car a few times, however it doesn't leak every day. I checked the coolant levels and it appears to be fine and the buzzer hasn't gone off. I also noticed some brown dirt-like substance at the top of my filler cap. Does this signal any major problems like oil getting into the coolant system. My car doesn't smoke at all on start up or while I'm under WOT.

 

If you still have your stock radiator- check the plastic endtanks as they will crack with age and leak under pressure. PM me if you need a new one-

 

could just be excess coolant from the overflow....

its easy to overfill her with coolant...

 

I recently had a coolant leak and I found it to be that my expansion tank had cracked. I have also heard that the coolant/air separator tends to crack due to heat, so you might want to look at that too. I would also suggest taking a good look at your hoses for tightness of the clamps and condition of the hoses.

 

could be a worn out radiator cap. old coolant turns brown,

 

the goop on the oil filler cap is normal, its condensation