1999 mazda millenia 84K, engine overheating - coolant is eaking,not located after pressure test. any ideas?

Question

been to dealership several times and did pressure test 6 times now. Can't find where coolant is leaking. Every 3 weeks, the entire coolant is below low/empty. Has anyone faced this before or have any ideas?

Answer 1

Replace the radiator cap regardless. It may be the culprit

Also, have them check the dipstick for the oil. See if the oil is a  milky white on the end of the dipstick. If it is, you have a leaking head gasket. This is terminable for the motor unless you get it repaired. If it is a leaky head gasket, water can leak into the cylinders. Since water doesn't burn, when the piston tries to compress it, it will be so much pressure that it will break the rod or spin the bearing.

Answer 2

I doubt it's the head gasket as suggested,  You would know that by now.  Based on your story, I'm betting on the water pump.  A water pump will hold pressure when not moving but then leak when going down the road.  That's why you can't find it.  Then engine is off and holding pressure.  Then when you drive it when the water pump is spinning it's slowly loosing water.  The bearing and seal are now allowing coolant to leak while in motion.

Also when they do the pressure test let it hold for 5 minutes.  It may not force water out but it may let the pressure leak down.  Also the radiator cap won't hurt but if you're loosing all your water.......it's not the cap.

Check along the bottom of the timing cover.  You may see coolant residue along the bottom.............it's a water pump if you do.  Change the timing belt while your at it.  

Answer 3

did they ever check the proper operation of the cooling fan,,?