Hello everyone, I got a 5.7 2015 M6 RT and today I noticed a big leak of hot coolant coming out of the small hose next to the reservoir cap (the hose that points straight down to the ground) It began leaking after I parked the car and turned the car off at home after leaving work. I turned the car back on for a couple minutes and the temp gauge was at halfway like usual. the fan didn’t turn on. however it stopped leaking when the car turned on. The reservoir looked bubbly/pressurizing while the coolant was coming out. The reservoir looks almost empty. Is it safe to drive to buy some coolant like this?

 

I don't believe that hose should be pointing to the ground. It should go to an overflow tank. It allows the increased pressure as coolant heats up to be purged into the container and drawn back in when coolant gets low/cools. It is normal for coolant to flow from there just should not go to ground. The pressure required for this exchange varies on vehicles and is controlled via spring pressure in radiator cap. If the hose is pointing to the ground then it likely got cut somehow. Happened on my XJ before from plastic retaining clip for hose breaking and it being able to get into fan.
edit. after reading your post again it sounds like you may be talking about the overflow not the radiator. If so...Is the overflow filled all the way to the top? Was it overfilled to begin with? it should have a line about halfway to indicate proper fill level when vehicle is cold.

 

I forgot to mention this is the 2nd time it’s happened. I took it to the dealer on a flatbed because I thought it was the transmission that was leaking. Turns out it was the coolant. But they didn’t explain why it was leaking. They just retopped the coolant

 

I would start by confirming a few things. first check coolant level in overflow, just to fill line not the top. Next confirm temp gauge is reading correctly. Using an infrared thermometer check temp near water pump. It won't be exact same but should be close to gauge. If not you could be overheating and the vehicle does not know, therefore it is not responding to bring on fan and cool it off. If that is good then I would move on to make sure fan can turn on (if it has aux fan) or speed up main fan. Sorry not too familiar with your exact vehicle but there will be some smarter guys around to help soon. You could be looking at water pump, thermostat or radiator cap as culprit. Water pump or partially stuck thermostat will restrict flow and cause high temp readings. Radiator cap could allow it to purge when it shouldn't. Is the coolant in overflow boiling? That is an easy indicator of overheated as it should not boil. When a molecule of water turns to steam it expands 1700 times it's size.

 

Hoses- Cracks, pinholes or splits in a radiator hose or heater hose will leak coolant. A hose leak will usually send a stream of hot coolant spraying out of the hose. A corroded hose connection or a loose or damaged hose clamp may also allow coolant to leak from the end of a hose.

 

Dealer said it’s the cylinder head..FML

 

Ouch !!

 

It wasn’t the heads after all. The gaskets and intake manifold seals busted, causing the gases to escape and pushing the coolant to shoot out the coolant bottle overflow hose.no signs of coolant went into the head. I should have my car done tomorrow