Hi this is my 1st post here. I recently got a 2012 3.7L V6 Mustang and since last week I noticed the antifreeze level was decreasing. I read many online forums but nothing related with my situation. Below are the things I have already checked for.
1. Checked for a pool of antifreeze below the car. No obvious leaks visible in the engine bay.
2. The engine oil is clear and no blue smoke. So mostly not a head gasket leak.
3. Checked for wet patches on the passenger side. Nothing there as well.
4. Need to do the pressure test. I have rented the kit and shall be doing the pressure test soon.

One thing I did notice is that the antifreeze level dropped only when I used the heater.
I have been using the AC everyday and there has been no issues. But since a few days after I started using the heater and a few times I had the heater on with the convertible top down and I noticed the antifreeze level dropped so quickly that within 2 days more than 1/2 the reservoir was empty.
I stopped using the heater since 3 days now and the antifreeze level has remained constant. I have used the AC during this time.
Please I need some help and advise.!!

 

Maybe the water pump was changed and had air in the system making the coolant level go down. Look and see if the water pump looks cleaner than other things in that area of the motor. This is 'if you are lucky'


If it is your heater core, there should be a wet place on your carpet.


I bet your water pump is going bad. Very common on our 3.7L

 

Thank you David, I have repeatedly checked for wet patches on the passenger side but its always dry. Yet this occurs only when I am using the heater. The water pump doesn't look like its been changed but I shall change it. Hopefully that solves the problem.

 

Blue smoke from the exhaust is burning oil. If it is burning antifreeze heavily it will be white. You can still have a bad head gasket and not see coolant in the oil, and if the leak is small it will burn off the antifreeze without the white smoke.

 

Don't know if the 3.7 is like the 4.6 but check under your intake manifold for wetness when you shut off the car. There may be a heater return line under the intake that goes into a head or crossover pipe. If it leaks from there, it usually drains out the rear of the engine bay and shows up near or under the tranny. or, it may be just be sloshing around in there.

Any musty sock smells? That's antifreeze when it burns.

 

Thanks a lot guys. I have got it resolved. It so appears that in that 1 week I was experiencing very cold mornings and the entire week I was starting the heater before actually waiting for the antifreeze to rise to normal functioning temperature. its been over a week and i have been using the AC and the heater and my coolant level has not dropped.

 

The coolant level should be constant regardless of when you turn your heater on. If you have a pint less coolant in your system from one week to the next, your car is burning it, or you have a slow leak somewhere where it's getting burnt off before it hits the ground (which was the case with my '98 Explorer which finally got air in the water pump and overheated one summer day). Check your oil for signs of coolant, and get your system pressure tested.

 

or you had air in the system and it's finally worked it's way out. you should be able to turn on your heater at any time without the coolant level changing

 

Thank you for your input guys.. The coolant level has remained constant since over a week now. I shall regularly monitor the coolant level.