Losing coolant
 

It started in the middle of winter and I cannot troubleshoot what the problem is. I have a 2013 mustang v6 and I am losing about a half a gallon of coolant every two weeks. It's not leaking out anywhere and it's not inside the engine nor do I smell coolant anywhere. I lose heat in the car and it blows out ice Cold air and I have to refill the plastic reservoir.

it started with my check engine light came on for not reaching the appropriate temperature in time so I replaced the thermostat as well as the gasket.

I also checked the oil and there is no coolant in the oil either.

As soon as I fill the reservoir backup my heat comes back again.

What could be causing me to lose so much coolant and not notice where it's going.

I'm not familiar with the 3.7 V6 but if there's a heater hose assembly in the valley of the engine below the intake manifold, that could be the source of the coolant leak.

Would that cause coolant to be puddled up anywhere or smell of coolant ? It's weird I don't see i anywhere, smell it, and the car doesn't overheat. It's like it just disappears.

Another possibility is that the cap on the coolant expansion reservoir isn't sealing properly and not allowing the cooling system to pressurize to 16psi, thus allowing the coolant to simply boil away.

The water pump is the 'weak link' on our 3.7 v6 motors. Use a small mirror and look around the bottom of the water pump. You should be able to see the 'weep hole', that's where your coolant will be leaking from 'IF' the water pump is going bad :(

How could I check the cap? It's def under pressure as when it's warm I can loosen the cap and hear the air escaping.

As for the water pump issue, where is it located, and I assume I check it with the car running and fully warmed up? Also, wouldn't this cause coolant to be on the ground? I live in cold weather and let my car warm up before I leave.

Don't check it with the motor running, you could get your hand cut off by the belt. It's on the front of the motor. Lots of 'youtube' videos on how to check and replace the water pump :)

The water pump is above the crank pulley at One O' Clock. When the water pump shaft seal fails, coolant will leak out from the weep hole but initially you may only see it immediately after you've shut off a fully warmed up engine. It's only when the leak becomes more advanced that you'll see it when the engine is running as well. A coolant leak may be so small that the only evidence you may find is staining or crusts around the source, so check all the coolant hoses and see if any of them look suspect.

Okay I checked the pump under different conditions and there's not even a trace of coolant leaking out of it. The entire front of the block is clean. I would suspect a small leak wouldnt allow almost a gallon of coolant to leak out every couple of weeks.

I'm not sure what else to check.

Have your system pressure checked when cold. Your system will get pumped up to 17-21 PSI and left at that with a gauge attached for a few hours. That's usually plenty to spot an external leak.