Your ZTS has either a PORSCHE designed engines or a MAZDA designed engine! My data base says a PORSCHE ONE! Perhaps you have a LEAKING WATER PUMP! Drive over any oil change pit and they can SEE if there are drips on your frame. Sometimes leaks will STOP when engine has stopped and not running at higher engine speeds! If you are NOT using genuine FORD COOLANT you are begging for trouble! NO PRESTONE ever and NO VALVOLINE OIL either! your FORD will love MOBIL ONE 0W-30 oil all it's lifetime! POWER WASH engine with gunk orange and allow it to DRY! Any leaks will be obvious. WRONG COOLANT can eat holes in the intake gaskets,but mostly on GM cars! .That engine is nearly BULLET PROOF and it DESERVES your kind attention to keeping it CLEAN inside and out! POWER WASH IT! BAD COOLANT cause GM BANKRUPTCY and multiple lawsuits for nearly ALL their engines! FORD did not have this problem as they TEST THOROUGHLY and genuinely care MORE! KEEP me informed! rgmuske@yahoo.com

When you have an inexpensive *cooling system pressure test you'll find the source of the external or internal cooling system leaks. If an internal leak is found a cylinder leak-down test will show exactly where the internal leak is found.

Not all internal cooling system leaks go into the crankcase.

if we have no external leak? then it must be ingesting it. this suggest a possible gasket issue e.g. inlet.

have we checked for antifreeze staining? e.g. under water pump ? in car ? is carpet damp ? how much are we adding?

anti-freeze either gets out on the windscreen or in the oil. The reason its disappearing is because it's being used- how did you think it worked?

You may never see milky oil. Many times with minor gasket leaks, a small bit of water is drawn in on the intake stroke, and all the coolant is expelled during the exhaust stroke. Since you have to top it off once a week or so, the leak is very small. Pressure is probably building up in your coolant system.

Check your oil dipstick and see if it has bubbles on. If so then you probably have a leaking head gasket letting coolant into the crankcase.

Most likely the heater core is leaking under the carpet. Do you have a "sweet" smell in the car's interior?

I have a 2002 ford focus zts that i have to add antifreeze to every week or two. Its not going into the engine, changed the oil and it was clean oil...not leaking from exhaust pipe, not leaking from anywhere. Thermostat has already been changed...where is it going