Mysterious coolant leak

needs to check it under pressure tester hand pump . mechanic has them . it should show you if and where the leak is. tighten all clamps up more and look for bad spots of rust of water leak areas. they can be hidden. replace hoses and maybe radiator to.

freeze plugs ( welsh plugs ) rust out and will leak water under pressure . they are replaceable with some difficulty-- working space required
water pumps will leak out a small hole under the housing behind the pulley to stop the leaking pump seal from putting water into the bearing-- replace is the only real fix as reconditioning is almost as expensive as a new pump
to find the leak have a pressure test done on the cooling system as it reveal where the leak is
if you have plastic radiator tanks then they are known to crack or even come loose of the cores
a pressure test will reveal all this

Put a piece of cardboard under the car. Then look down at the cardboard from above the the area. You can see where the drops are in relation to the hose or water pump or other spot.
I do that for locating oil leaks.
Hope this helps.

Water pump is going out.

how about the heater core?most times it will leak inside the vehicle.. but its just a guess

"Mystery leaks" can be very frustrating..You have a leak somewhere, guaranteed. Check all hose connections, hoses, the thermostat housing gasket, the water pump gasket, and the water pump itself (check it last). Try this: park the car overnight inside a garage immediately after driving it while it is still hot. Park it over a large piece of cardboard. Antifreeze is, among other things, oily in nature, and will stain the cardboard where the coolant drips onto it. The areas that get stained are not necessarily the area from which the coolant leaks--water travels along various surfaces until it reaches a low enough spot to drip from, But if you have a stain, even a small one, smell it...if it's antifreeze, check everything again. Sometimes you have a pinhole in a hose so small it is only open and spraying coolant when the system is at temperature and under pressure. Keep looking; you'll find it. If I helped you, please vote/comment, and good luck.

Radiator or hose.

If you can narrow down where the leak is coming from, it will be easier for you to fix, but it is most likely either a minor radiator leak, or your water pump. You can put a can of radiator stop leak in your vehicle, such as bars leak. It wont hurt anything. If the leak continues, and appears to be coming from the engine area, the water pump is failing, but also check around the thermostat housing, near where the upper radiator hose connects to the engine

Hi:
Coolant leaks can be tough to figure out where they are leaking, because it is tough to check around on a warm, running engine! I hope it isn't your recently changed water pump, but you can't rule that out. To help narrow things down, you can put papers down on your garage floor, and get a better idea as to what area under the hood it is leaking from, such as directly under the radiator, left side, right side, etc. Using a safe cooling system stop leak product is an option too. Bahrs leak is put in the radiator of every brand new car, and is a safe bet to aid in stoping a small leak. Either way, you need to narrow your search area if you want to find the problem, so work that first!

with my experiance on these engines it's usually the upper outlet hoses running from the heads into a t then into the upper radiator hose they are pain to replace but 3 out of 3 of my v6 isuzu's have had the same problem you'll have to pull off the theromstat and the coil pack the hoses are very small and run from the end of the heads one on each into a t then into the radiator hose just under the housing