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Discussion Starter #1
I'm embarrased to say, I've never back-flushed a heater core. I've never needed to. Anyway, I don't trust my local dealership to make a proper go of it, so I'm doing it myself.

  • Do I need to flush the heater core?
  • Should I flush the heater core?
  • If yes, which heater core hose is the output hose?
  • If no, will flushing the coolant also flush the heater core?

My main concern is the coolant, of course. The coolent in the tank doesn't look like the correct color, so I want to get all of whatever is in there, out. I'm not going to replace the stock t-stat with a 180 degree t-stat, so it should be pretty straight forward.

  • Should replace the OEM t-stat with a fresh one?
  • If the coolant is HOAT, what kind of damage could it have done to my 2016 R/T?

I just want to make sure it's done correctly.
 

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2018 Dodge Challenger T/A Plus in Yellow Jacket w/5.7L and A8 automatic
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How many miles are on the car? Is the coolant color your main suspicion?
 

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Discussion Starter #3
How many miles are on the car? Is the coolant color your main suspicion?
Less than 21k. I just want to make sure the system is clean. I have a vacuum lift device coming, so that I don't have to mess with bleeding air from the system. I'm concerned about making sure the heater core gets filled as well. I assume the vacuum lift system takes fluid throughout the entire system? I guess I won't mess with backwashing the heater core. Not unless it needs to be done. I was planning on draining the coolant, filling it with water and Prestone radiator flush, drain the flush, rinse with more water, then recharge with the vacuum lift and Mopar coolant. The one thing that baffles me, is how the vacuum can pull air from/coolant through the system, when there's a closed t-stat in the system?
 

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2018 Dodge Challenger T/A Plus in Yellow Jacket w/5.7L and A8 automatic
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Did you buy the car new? If so....has the car ever had any cooling system related work performed on it?
 

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Discussion Starter #5
Did you buy the car new? If so....has the car ever had any cooling system related work performed on it?
Purchased it used. No cooling related work that I'm aware of.
 

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2018 Dodge Challenger T/A Plus in Yellow Jacket w/5.7L and A8 automatic
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Going off memory here......but I think FCA actually offered the OAT coolant in two colors. One color was unique to the Dodge Ram Chrysler Jeep family, and the other was unique to Fiat.
 

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The Pork Wagon (‘14 Cop Charger)
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At 4 years and only 21K miles, there should be no corrosion or rust issues that would necessitate extra effort during a coolant change. Just drain the system completely, run pure water through it a few days to flush it out if you want, then refill with the proper coolant (Purple OAT most likely) mixed at a 50/50 ratio with purified or distilled water (non-tap in other words). BLAMMO! You’re good to go until 2025-ish or 125K miles on the odometer, whichever comes first.

If you are truly concerned about the system needing a thorough flush to remove contaminants, check the condition of the inside walls of the coolant overflow reservoir. If you see lots of deposits stuck to the inside of that container, they are also going to be throughout the cooling system and need to be addressed in some fashion.

But I would be shocked if your system were in that bad of a shape after so few miles and only 4 years.
 
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The Pork Wagon (‘14 Cop Charger)
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Also, there is no reason to replace the OE thermostat right now unless you just want to run a lower temp one. The OE unit will be good for another 100K miles at least, likely much longer.
 
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Discussion Starter #9
Also, there is no reason to replace the OE thermostat right now unless you just want to run a lower temp one. The OE unit will be good for another 100K miles at least, likely much longer.
Thank you! I've heard that Dodge heater cores fail as a result of particulate matter from production, that they should be backwashed before they leave the plant. I can't see where that's true though... I worked in the line at Ford Motor, and don't every recall this being an issue. I suppose failures could be do to materials, but I doubt it. I've seen videos clips where people are sending CLR through their aluminium heater core! I can't think of a better what to trash a piece of aluminium than to hit it with acid. It may not effect the surface metal to large extent, but the welds are another story.

I'm not hip on using a 180 t-stat on newer engines. Not with the kind of tolerances they're using today. Part of getting the engine up to spec temperature is so that the oil can flow properly within a minimal amount of time. Once the coolant reaches 200 degrees, the t-stat is running wide open; same as a 180 t-stat. If engines are running too hot with the stock t-stat, there's something else going on. If anything, I'd be looking at an aftermarket radiator/fan assembly.
 

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2020 Challenger R/T Scat Pak
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As said above, if the coolant tank is clean I wouldn't use a flush.

Think of the thermostat as one valve in a loop. When you pull a vacuum on the system, you are pulling from both sides of that valve. A vacuum system should clear the heater core and all hoses whether the thermostat is open or closed.

I don't know about the thermostat in our hemi's because I haven't had an opportunity to look at one up close yet but some have a small diameter vent hole in them which would help with evacuation.

DeWFPo
 

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Discussion Starter #11
As said above, if the coolant tank is clean I wouldn't use a flush.

Think of the thermostat as one valve in a loop. When you pull a vacuum on the system, you are pulling from both sides of that valve. A vacuum system should clear the heater core and all hoses whether the thermostat is open or closed.

I don't know about the thermostat in our hemi's because I haven't had an opportunity to look at one up close yet but some have a small diameter vent hole in them which would help with evacuation.

DeWFPo
Understood. Makes perfect sense. The coolant doesn't look clean to me. Like I said, I don't know if someone mixed HOAT with OAT, so I'll give it a good flush to be sure. I suppose I don't really need to know which core hose is which, since I'm going to flush in both directions. It's more a matter of knowing that my system is up to spec as can be.
 

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The Pork Wagon (‘14 Cop Charger)
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Understood. Makes perfect sense. The coolant doesn't look clean to me. Like I said, I don't know if someone mixed HOAT with OAT, so I'll give it a good flush to be sure. I suppose I don't really need to know which core hose is which, since I'm going to flush in both directions. It's more a matter of knowing that my system is up to spec as can be.
If you plan on man-handling the hoses on the heater core inlet/outlet tubes, be careful not to snap one of those tubes off with the hose removal/installation. That will necessitate a heater core replacement, and adding that job to what started out as a coolant system flush will turn the whole thing into an ordeal.

If the heater cores in these Dodge LX cars have issues from the factory, I have not run across it yet. I’m on my 4th LX car, and between them all, I’ve probably flushed the system a dozen times at least. At no point did the heater core belch forth any abnormal material or fail to perform when asked to provide hot air.

Also one more FYI - if I’m not mistaken, I believe these cars’ heater cores get coolant circulated all the time, not just when the heater is on. So there is no need to stop halfway through any filling or testing steps in all this to make sure the heater is turned on. For all intents and purposes related to this task, you can consider it ‘always on’ I do believe.
 

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With the heater on, shoot the heater core hoses with an IR temp gun (if you have one) and you'll know which is IN and which is OUT.

DeWFPo
 

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Discussion Starter #14
If you plan on man-handling the hoses on the heater core inlet/outlet tubes, be careful not to snap one of those tubes off with the hose removal/installation. That will necessitate a heater core replacement, and adding that job to what started out as a coolant system flush will turn the whole thing into an ordeal.

If the heater cores in these Dodge LX cars have issues from the factory, I have not run across it yet. I’m on my 4th LX car, and between them all, I’ve probably flushed the system a dozen times at least. At no point did the heater core belch forth any abnormal material or fail to perform when asked to provide hot air.

Also one more FYI - if I’m not mistaken, I believe these cars’ heater cores get coolant circulated all the time, not just when the heater is on. So there is no need to stop halfway through any filling or testing steps in all this to make sure the heater is turned on. For all intents and purposes related to this task, you can consider it ‘always on’ I do believe.
Understood. Good advice! If I do flush the core, I'll access the ports from the other end of the hoses. I think I'm just going to drain the system, vacuum lift and refill.
 

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Discussion Starter #15
With the heater on, shoot the heater core hoses with an IR temp gun (if you have one) and you'll know which is IN and which is OUT.

DeWFPo
I just got through looking at the diagram... The inlet is the bottom tube.
 

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The Pork Wagon (‘14 Cop Charger)
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I just got through looking at the diagram... The inlet is the bottom tube.
You sure?

I’m sitting here looking at mine and imagining the flow of the coolant based upon the reservoir inlet and outlet hoses and which of the heater core hoses those connect to, and it seems to me that the only way the coolant could flow would be for the top hose to be the inlet and the bottom to be the outlet.

1006903
1006904
1006905
K

We know the top hose on the reservoir is its inlet, and the bottom is the outlet. And we can see each of those connects to its corresponding heater hose in the same relative position - top to top and bottom to bottom.

Plus the bottom hose feeds that overflow tubeunder the intake that runs up to the water pump and ingresses over the impeller.

And accordingly the top hose connects to the intake as if the warm water coming through and out of the block is now ready to heat the air in the cab via the heater core.

I ain’t saying I’m absolutely right here, but it makes so much sense to me that if I am wrong, I may have to rethink some very serious life choices I’ve made recently 😬
 

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Wouldn't running the heater circulate through the heater core?

A Guy
 

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2020 Dodge Challenger Hellraisin Scat Pack
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Wouldn't running the heater circulate through the heater core?

A Guy
Yes. In fact my info is many car heating systems have the coolant flowing through the heater all the time. The degree of cabin air heating is controlled by an air flap.

With the coolant flowing through the heater core all the time there is no valve hardware to go bad and the constant flow keeps corrosion at a minimum.
 

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My two cents...

Any flush other than possibly just a temporary fill with plain tap water and running the engine to full operating temperature is unnecessary.

However, there are exceptions:

Any chance the cooling system has been run with no anti freeze or has been contaminated with oil or some goofy anti freeze replacement or even an incompatible type of anti freeze with what you are goingi to use when you refill the system should have the system flushed using a good cooling system flush fluid. I have never had to do this use any of this cooling system flush stuff so I have no recommendation. My inclination would be to speak to a tech and ask his recommendation. Or if Dodge (Mopar) offers an off the shelf cooing system flush fluid use that. (Chances are it is just a relabled off the shelf flush fluid.)

The heater core will be "flushed" along with the rest of the system. Turn the heat setting to max. In some cars this ensures full flow of coolant through the heater core. However, a number of cars nowadays -- actually from way back in 2002 and maybe earlier -- have a valveless heater core. The coolant flows unchecked through the heater core. The amount of heating of cabin air is controlled by the temperature control on the dash which in turn controls an air flap.

Generally the T-stat is not replaced until the water pump is replaced. Almost always the water pump goes bad "first". I'm of two minds here. If you do not disturb the T-Stat during this "flushing" business leave the T-stat alone.

If you have to remove it after all the flushing is over with and you are ready to button the system up prior to its last refill replace the T-stat with a factory T-stat, same temperature. Before you install the new T-stat drop the new and old T-stats in a pot of water and heat the water on the stove and using a digital cooking thermometer verify the new T-stat opens at the right temperature and opens fully. IOWs its movement should be very much like the old T-stat's movement.

I do not know what if any "damage" using HOAT anti freeze can do to a cooling system. Obviously any bad cooling system components should be replaced after the system is drained and before any flushing or final refill is done.
 

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Discussion Starter #20
You sure?

I’m sitting here looking at mine and imagining the flow of the coolant based upon the reservoir inlet and outlet hoses and which of the heater core hoses those connect to, and it seems to me that the only way the coolant could flow would be for the top hose to be the inlet and the bottom to be the outlet.

View attachment 1006903 View attachment 1006904

We know the top hose on the reservoir is its inlet, and the bottom is the outlet. And we can see each of those connects to its corresponding heater hose in the same relative position - top to top and bottom to bottom.

Plus the bottom hose feeds that overflow tubeunder the intake that runs up to the water pump and ingresses over the impeller.

And accordingly the top hose connects to the intake as if the warm water coming through and out of the block is now ready to heat the air in the cab via the heater core.

I ain’t saying I’m absolutely right here, but it makes so much sense to me that if I am wrong, I may have to rethink some very serious life choices I’ve made recently 😬
That's what the hose diagram indicates. Unless the diagram I looked at corresponds to a different vehicle? Wouldn't be the first time, that's for sure.
 
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