Coolant System Issue

[rnr3.7]

I drive a 2015 V6 mustang with about 53,000 miles on it. One day after about an hour of driving I parked it on the street. A couple hours hours later I drove it to go golfing 20 minutes away. My dad called me to tell me I felt a puddle of coolant in my parking spot on the street. The reservoir was low, so I topped it off when I came home. I checked for leaks and found fluid, but could not track where it was coming from. I rented a pressure test and found it wasn’t holding any pressure. Pressure wouldn’t build up and decrease over time, but it wouldn’t hold pressure at all to begin with. I checked for more leaks when doing this and couldn’t find anything. I then took of for a drive and there was still no leaks, no overheating, nothing! I am thinking about getting radiator stop leak concrete, but am unsure if that will do anything. Please let me know if you guys have any other ideas, thanks in advance.

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[ORRadtech]

Do NOT use a stop leak product, period!
Check the exhaust for unusual steam/smoke and a sweet smell, check the coolant tank for an oily sheen, check the oil for a milkshake look.
Put it on a lift/jack stand and look from underneath at all the houses including the heater hoses. Also look at the freeze plugs.

 

[rnr3.7]

Do NOT use a stop leak product, period!
Check the exhaust for unusual steam/smoke and a sweet smell, check the coolant tank for an oily sheen, check the oil for a milkshake look.
Put it on a lift/jack stand and look from underneath at all the houses including the heater hoses. Also look at the freeze plugs.

Do NOT use a stop leak product, period!
Check the exhaust for unusual steam/smoke and a sweet smell, check the coolant tank for an oily sheen, check the oil for a milkshake look.
Put it on a lift/jack stand and look from underneath at all the houses including the heater hoses. Also look at the freeze plugs.

There is no smoke or sweet smell from the exhaust. I checked the coolant tank and there is an oily sheen on the top. I checked the dipstick and the oil looked normal. I recently replaced the spark plugs and has to take off the intake manifold. It’s possible it isn’t tight enough or seated properly. Would this cause the issue?

 

[rnr3.7]

Learn what antifreeze smells like. Get a bottle and pour it on a rag and smell it for a half hour. There is no other smell like it.

You most likely misused the pressure tester. If it won’t hold pressure it will boil the antifreeze and overheat.

Park the car on a flat piece of ground when it is leaking see which side the antifreeze is pooling on. That will give you a start to where to look.

The coolant does not leak anymore, it was only that one time (which is weird). when I get the car up to temp it is not overheating and there is no pressure in the coolant lines

 

[cop on my back]

I just went through a very similar issue with my girlfriend's 2014 GT. I found the leak and replaced the upper rad hose (not cheap) still leaked. Turns out it was corrosion on the aluminum spigot on the thermostat housing where the t fitting hose fits. It was swelling up to the point it started to leak. I removed that hose, cleaned off all the corrosion and dried coolant and no more leaks.

Not sure how the v6 coolant hoses compare but I bet they are fairly similar.

 

[rnr3.7]

I am not sure you understand a cooling system. Antifreeze and water boil at 226 degrees under no pressure. As the pressure increases the boiling point rises. Your system has to have pressure unless you are running it under 226 degrees which can happen at times but not when the car is hot.

Antifreeze leaks don’t go away. Not trying to be an ass just have been though this many times over the years. BTW NEVER pour tap water in the engine. Only distilled water. Water our of an A/C system is the cheapest distilled water you can get.

So I just did the pressure test again today and nothing again. I ran the car for a while and removed the cap slowly (I know I shouldn’t do that) and I could hear some pressure escape. the coolant leaked that one time and then never again. I have checked after each ride. when I filled it, I used more coolant and not water

 

[rnr3.7]

I just went through a very similar issue with my girlfriend's 2014 GT. I found the leak and replaced the upper rad hose (not cheap) still leaked. Turns out it was corrosion on the aluminum spigot on the thermostat housing where the t fitting hose fits. It was swelling up to the point it started to leak. I removed that hose, cleaned off all the corrosion and dried coolant and no more leaks.

Not sure how the v6 coolant hoses compare but I bet they are fairly similar.

The thermostat housing is above where I think the leak was coming from, but it hasn’t leaked again since that day. it could be the issue but I would expect it to repeat again after driving it

 

[rnr3.7]

It’s probably the cooler temps not building the same pressure as the warmer days. Regardless it will show up again as long as you know what coolant smells like, you will smell it instantly. I smell people’s leaks sitting at red lights. As long as you keep it full it won’t hurt anything in the short term.

Little chart that might help with pressure.

It was a large puddle the one time it happened so I don’t think it will be a small leak when it happens again. I appreciate your help and will update if I notice a leak in the future

 

[lacanteen]

Similar thing happened to my F150. A slow unfindable leak. It was the water pump. Had a slow leak that only dripped when hot and running.

 

[Soulja4187]

Did you by mistake tap on the radiator drain plug? Make sure it's on tight I seen leaks come from there when the car gets got

 

[Cobra Jet]

Check the following:

Small hose coming off the coolant bottle - many have reported finding small cracks or tears in the hose where it slides over the nipple. You have to really inspect these hoses.

The nipple coming off the bottle - again check for any damages on it or where it’s molded to the bottle (small fractures or cracks).

Water pump - usually when a water pump starts going it has a weep hole and the coolant will seep from the weep hole (usually on underside of the pump shaft).

Tighten all clamps you see on all coolant hoses. Rubber hoses contract and expand with heat/pressure. Just because clamps visually look “fine” doesn’t mean they are properly secured to prevent leaks/seepage.

Radiator - you would need a black light for this test. Using a black light shine it on the back side of radiator. If there is a pinhole leak in any of the core rows you’ll find it with a black light. Again if it is a pinhole leak it may not be visible or easily seen without a black light - and usually it won’t “spray” under pressure all the time, it will weep out and be hidden within the core structure, slowly dribbling down onto the street or garage flooring. Another way a radiator can leak is at the core tanks where the tank meets to core rows. Usually it won’t spray under pressure if the damage is not significant, but will seep enough to leave puddles.

 

[rnr3.7]

I drove the car today for about 40 minutes. Still no more leaks, but the system is holding pressure now. I’m thinking the pressure test wasn’t sealed correctly. I am going to look over it again this weekend to make sure everything is tight and sealed. Will update if I notice another leak, big or small.

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