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Challenger SRT 392
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Discussion Starter · #1 · (Edited)
Hi All,

So after topping of my coolant in my 2016 Challenger SRT 392, every time I park, there is a significant puddle of coolant on the ground... Long tory short, I let the engine come up to temp at idle with the cap off, and right before the fans kick on, the reservoir will bubble and overflow. Put the cap back on, and it continues to rise until it runs out of the overflow flow tube.

The level will rise for a few minutes, and then the thermostat opens and the fan kicks on, and then the level will go back down. My thought is if the overflowing coolant is normal with the cap off, then my overflow cap is bad and letting coolant out the overflow drain tube when hot.

Thanks in advance for the help!

EDIT: Problem was fixed with a new cap. The old one was not allowing the system to build pressure, as the coolant would just push past the cap and out the overflow.
 

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Charger SRT Hellcat
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917 Posts
Dumb question, but are you topping it off cold, or maybe over filling?
 

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Challenger SRT 392
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Discussion Starter · #3 ·
Yes, definitely topping off cold. The level will rise and then go back down when the fans kick on and the thermostat opens. I have a video I can upload later.

I guess my question would be, will a bad cap cause coolant to push past and go out the overflow tube?

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2020 Challenger Hellraisin Scat Pack.
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With the cap off there is no pressure in the cooling system. Coolant at the hottest places in the engine can flash to steam and the resulting bubbles of steam can force the coolant to "bubble" and overflow. Like a full pan of water on a hot stove burner. It is normal behavior.

What is not normal is to run the cooling system any length of time with the cap removed.

Pressure is critical to the proper functioning of a cooling system.

The puddle on the ground is almost certainly a leak.

My advice is to clean the cap. Put it under a running faucet. Clean the threads of the coolant tank and the surface against which the cap seats/seals.

With the engine cold add distilled water to bring the coolant level up to some reasonable level. In the middle of the low and max lines is "best".

Be sure the cap is screwed on to the tank threads correctly and then be sure the cap is tight. To someone not used to removing/installing a coolant cap the force required can be surprisingly large. But you do not want to over tighten the cap, either.

Turn off the A/C. Start the engine and then drive around town to get the engine up to temperature. In this context that is hot enough that the T-stat is open and the radiator fan is coming on. My observation with my 3 Challengers has been this occurs around the 216F temperature.

Go home. On your driveway raise RPMs to 1K or just a bit over. Hold until the radiator fan turns on. Shut off the engine.

Wait.

The heat load of the engine will raise coolant temperature and pressure. With everything hot if there is a leak it will make itself known.

With the cooling system level good and the engine/cooling system hot and under pressure If there is a leak -- and the puddle is an obvious sign there is a leak (obviously) -- I think you'll know where it is.

Be careful. The cooling system is under considerable pressure and if the leak is major such as was the case with the bad coolant tank, hot coolant under pressure -- and driven by the hot coolant which when pressure drops will boil -- can spray out. A face full of this can ruin your day.
 

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Charger SRT Hellcat
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Coolant reservoir bubbles?????? Bone stock? I may look elsewhere then.
 

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Challenger SRT 392
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Discussion Starter · #6 ·
It was a bad cap after all. When the system would build pressure, the cap was letting coolant out of the overflow tube. With a new cap, the level has been steady

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