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Coolant Flush

Im doing a coolant flush. I’ve turned the pepcock valve and not a drop of coolant flows out. Possible clog? Any ideas?

Yup, Remove the lower radiator hose and drain from there.


Agree. Usually those petcocks are hard to get to and before you know it the whole thing comes out. Also unless you are trying to resolve a cooling problem, I’d forget the flush and just do a drain and refill.

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The fluid is in need of changing. Clogged pepcock makes me think it could benefit from a from a full coolant flush. Have to take the shields off to get to that bottom rad hose.

This may sound stupid, but have you removed the radiator cap? What kind of vehicle? BTW, petcock.

I have yeah, the drainoff hose coming off just under the cap keeps it from being a totally closed vacuum system.
It’s an '09 5.7 Charger RT with custom intake and exhaust.

I’m not familiar with the petcock used on that one, but some petcocks are quarter turn, some are threaded and some are quarter turn but the valve must move outward about a half inch in that quarter turn. Some of the latter have a quarter turn where the calve doesn’t move out and then comes out about a half inch on the second quarter turn for a total of a half turn.

Most petcocks today only have about an 1/8" - 3/16" hole to drain out of so draining can take a long time. Removing the lower hose dumps all the coolant at once and makes a mess. I’ve also had petcocks that wont seal back up and have to be replaced.

Agree with just drain and fill. Flushes can do more harm than good in my experience.

Totally remove the Petcock plug and see if coolant drains out.

If not, take something like a small screwdriver, and poke it into the Petcock/radiator tank to see if unplugs the clog.


Looked yours up, threaded type, about one full turn for drain.

An entire turn, 360°? Seems like it only wants to go 90°, open/closed. Ill have to have another look.

It may take 3-4 turns of the Petcock valve before it will start draining coolant.


If you have a compressor…and can get a spray tip close enough …you may be able to free the clog by blowing into it.


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What type of harm have you seen in your travels via coolant flush ?

Your Chrysler product might be like mine: the petcock is a bayonet mount. It needs to be turned (1/4? 1/2? turn) (CW or CCW?) and pulled out. It can take quite a yank.

I don’t own Fiat/Chrysler products?


Not true. That is only open when pressure in the system exceeds the rating of the radiator cap.

The radiator cap will let air into the cooling system so the hoses don’t collapse when the cooling system cools. Engines are usually hot when I bring a car in to the shop and the cooling system is under pressure so I begin draining the cooling system with the cap on, the radiator will draw all the coolant from the reservoir, then air into the radiator.

Managed to remove the petcock with a twist and pull. Flow increased quite a bit after removing the rad cap.
Had a bit of a issue refilling with distilled water/cleaner due to an airlock type situation. Any tips on properly filling coolant system from empty to avoid air lock?

There is a plug near the water outlet, remove the plug and refill the cooling system with the engine off, this will allow the air to escape while refilling the cooling system.

The air lock seemed to be within the engine/coolant lines as opposed to the reservoir itself. I’ll try to add the coolant slower and run the engine so it’ll be drawn through the lines.
Lots of good info above. Thanks very much👍