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New to this forum so hi, just picked up a 2012 300c 5.7 and I get home to see the coolant is very dirty, old coolant is stuck on the sides of the res and quite thick along the top. I was told by a 300s owner not to completely flush it but to drain it, rinse the red and the hoses, and reapply coolant cause doing the “flush multiple times until water is clear then re add coolant” way would make matters worse . Too me if it’s that thick and dirty I’d think it should all get cleaned out completely? Anxious for answers.

Thank you
 

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Welcome aboard!

That's likely rust that you're seeing, not coolant residue.

It works like this; modern, reasonably fresh HOAT coolant does a great job preventing rust.

As it ages and the additive package is depleted, it doesn't perform quite as well, so you may see some corrosion. But the bigger culprit is low coolant levels. As your coolant level drops and metal surfaces in your radiator are exposed to air, they begin to corrode almost immediately. This problem is exacerbated by any leaks you might have which introduce air into the cooling system.

When you top off with fresh coolant, much of the rust washes off and rises to the top (your coolant reservior), making your reservoir look like someone puked in it.

The first order of business is deciding whether it's worth your time to clean the reservoir or replace it for $50-75 or so.

I've found that the best way to clean it is to remove it, fill about halfway with the hottest water you can, mixed with Lemi-Shine, a little automatic dishwasher (not dishwashing) liquid and a small handful of BBs, and shake that thing like crazy. It's full of tiny compartments that are extremely difficult to clean, that's where agitation with BBs helps. Drain, rinse, repeat til clean.

In terms of replacing your coolant, I'm a drain-and-refill guy. There are many great posts, here and on our sister sites, with tips about flushing. But IMHO, there are too many posts about chasing air bubbles after a flush. Here's the very slow but simple process I use:

Take off the radiator cap, open the petcock, and drain the radiator. Kind of a mixed bag FCA gives us here...they were thoughtful enough to include an S-shaped hose to drain easily and cleanly into whatever pan or vessel you place under the car, but they also use a really cheap, crappy plastic petcock that always seems on the verge of breaking.

Once finished draining, close the petcock. I prefer to let the car cool down for a while at this point. Slowly pour in distilled water (less than a buck at your local Wallyworld) until your reservoir is at the "full" mark. Then start the engine and watch your temp gauge and reservoir carefully. Note the temp when your coolant begins to actively "percolate" (not just a few small bubbles). Don't let that go on for more than a few moments. Drain the radiator again. Repeat this process until the drained fluid comes out clean enough for you.

Once the drained fluid is reasonably clear (it won't be crystal-clear without flushing or pulling your block plugs), refill slowly with concentrate (not 50/50 premix) of your choice of HOAT coolant. I would suggest either Motorcraft Gold or Zerex G-05. If you want gen-yoo-wine Chrysler fluid, do your research and get the part number. Do not trust the dealer to provide the correct coolant without the part number. Go through the same refill/drain process you used before, until you get the mix you desire. I like 50/50, but check your owner's manual to see what Chrysler recommends, it's probably more like 55/45 coolant/water. If you don't have a coolant tester, grab one for about $5.

Once the mix is where it belongs, let the car cool completely and run it up with the radiator cap off. Top off as needed, and check it (warm and cold) for the next couple of days.

Good luck!
 

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Be careful, somewhere around 2012 Chrysler changed from HOAT to OAT - they don't mix. If that's happened that could be the problem

Personally I would drain and replace with a clean mix. Be careful even if you buy from Chrysler, my local dealer tried to sell me the wrong stuff!
 

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Discussion Starter #4
I appreciate all of that man. Turns out the cooler for the trans in the radiator leaked into the coolant. I flushed it 4 times and every time it was the same shade of reddish. Not much like rusty water but when I figured it out it made sense that the color wouldn’t change due to the tranny fluid leaking into my fresh water I was flushing. So need less to say, verdict is...

New radiator
Trans flush

Thanks man💪🏻
 

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Discussion Starter #5
Be careful, somewhere around 2012 Chrysler changed from HOAT to OAT - they don't mix. If that's happened that could be the problem

Personally I would drain and replace with a clean mix. Be careful even if you buy from Chrysler, my local dealer tried to sell me the wrong stuff!
I’ll triple check with them before I fill it back up. I have the coolant from Chrysler but that’s about the 4th time now I heard they might not give me the correct coolant.

Thanks
 
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