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(mods please move to an appropriate section as necessary)

I recently had to flush and refill my JK's 3.6 Pentastar coolant and thought I'd share the procedure I followed.


Reasons for coolant replacement/flushing
  • Coolant has reached 10 years/150,000 miles
  • Cooling system isn’t working efficiently
  • Fixing a leak or replacing thermostat (not covered in this writeup)
  • Accidental mixing of coolant types or not sure what’s in your engine
  • Coolant contamination with non-distilled water
  • Heater core plugged/not enough heat
Overview of Pentastar cooling system

Coolant is forced through the engine block by the serpentine belt-driven water pump.

Coolant exits the oil intercooler in the Vee of the engine (below the oil filter) and returns via a hose to the water pump.

Hot coolant also exits the engine block at the front before the thermostat (under the alternator), is routed to the heater core then returns to the water pump via the same return hose as the water from the oil intercooler.

The main flow of coolant exits the block via the thermostat at the front of the block, is fed to the radiator via the top radiator hose, and returns to the water pump via the bottom radiator hose (which comes out halfway down the radiator on passenger side)

The radiator has a safety/fill valve at the top, with an overflow hose leading to the coolant bottle. If pressure is too high, excess coolant is sent to the bottle. If a vacuum is present once the engine cools down, coolant is sucked from the bottle back to the radiator.

Some Pentastar engines have EGR cooling (i.e. Jeep JL), I didn’t check if my 2014 had that.

Tools & supplies
  • Flat screwdriver
  • Hose clamp pliers or regular pliers
  • Hose pick or small flat screwdriver to help pry hoses off hard lines
  • Spill-proof radiator coolant filling funnel kit
  • 5/8 O.D. plastic tubing
  • Coolant flush adapters
  • Coolant flush/cleaner like Prestone
  • Distilled water
  • OAT concentrate or 50/50 mix. Full system capacity is listed at 11.4 quarts however I could only put 8 quarts in there, not sure why. NOTE: 2012 model use HOAT, not OAT!
  • Buckets to catch coolant
  • Containers to recycle coolant
Before flushing
If coolant is really dirty or cooling/heating performance isn’t good, drain 1qt coolant & add 1 qt coolant cleaner, then drive the Jeep a few hours over a few days.


Draining the coolant
Engine must be completely cooled before proceeding!

1. Place buckets under the engine & radiator to catch coolant
2. Remove grille to access radiator petcock (on Rubicon models, the sway bar motor makes accessing petcock from below pretty much impossible)


3. Open petcock (counterclockwise, 1/2 turn)
4. Open radiator cap
5. Disconnect hose at cap, remove coolant bottle; it’s held by one black plastic rivet, then pulls right up; drain & clean bottle


6. Disconnect upper radiator hose at thermostat housing
7. Disconnect lower radiator hose at water pump; that hose is U-shaped, so there’s coolant trapped in there. Removing air intake makes it easier, but isn’t necessary.


8. Disconnect heater core hoses and oil heat exchanger return hose




Flushing

9. Using plastic tubing, reverse flush heater core through return hose until water runs clear; do not use too much pressure, the system is only designed for 10-15 PSI not the 50 PSI your home water system may produce!


10. Blow air through heater core return hose to flush out water; use LOW air pressure from a compressor, or just blow by mouth (don’t swallow coolant!)
11. Using plastic tubing, reverse flush engine block through oil heat exchanger return hose until water runs clear
12. Blow air through oil heat exchanger return hose to flush out water
13. Connect plastic tubing, reverse flush engine block through metal line to thermostat. Then blow air through it.
14. If possible, reverse flush radiator through lower (return) radiator hose; otherwise just flush water through the top radiator hose inlet
15. Let radiator drain completely


Refilling

16. Reconnect both radiator hoses, close petcock
17. Reinstall grille
18. Reinstall and reconnect coolant bottle
19. Connect coolant fill funnel using adapter for radiator cap


20. Start filling radiator with coolant mix until coolant comes out of the metal heater lines
21. Feed coolant into one of the heater core hoses until it come out the other; this fills the heater core.
22. Reconnect heater core hoses to metal lines
23. Feed some coolant into oil heat exchanger return hose until it overflows
24. Reconnect oil heat exchanger hose to metal line
25. Fill radiator and leave funnel in place; there should be 1-2 inches of coolant in the funnel
26. Fill coolant bottle to cold mark
27. Start engine and let it come up to operating temperature; monitor temp gauge (and if your Jeep has EVIC, the digital temp display.) Temperature should come up gradually to 200F or so and not spike.
28. Let engine run 10 minutes or so. Monitor temp, and filling funnel; don't let funnel run dry, add coolant to maintain 1-2 inches level. As the thermostat starts opening, coolant in funnel may rise; if it’s about to overflow or boils over, stop the engine for a minute or two.
29. Turn off the engine; you’ll observe air bubbles coming up in the funnel. After a couple of minutes restart the engine for 5 minutes. Rev it once or twice to force air bubbles out. Repeat this procedure several times until no more bubbles come out.
30. Let engine cool down a bit then remove funnel and reinstall radiator cap. Top off coolant in bottle to full mark.
31. Take a test drive if you want, and make sure you get heat (if you don’t you probably have air in the heater core) Then shut down the Jeep and let it cool down. Once fully cooled (several hours) check coolant bottle and add coolant if necessary.

For a more complete flush, fill with distilled water (with or without cleaner), bring engine to operating temperature, then let cool and repeat procedure as necessary, refilling with 50/50 coolant mix the last time.
Recycle all used coolant & flushing water. Remember that stuff is toxic to pets, humans and the environment.


Some videos that I found useful



 

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This is the type of write up that makes forums great. I've attempted to provide writeups on other vehicles I've owned and understand how much additional time this took to do instead of just doing the work. I appreciate you making the effort to do this for other folks. I'm pretty far from needing to do this myself but you're writeup is so great that I'm going to take the time to convert to a pdf with all the pictures included to make sure I have it in a few years. Congrats on a job well done!
 

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Discussion Starter #7
Great step by step! Thank you.

How do you dispose of the waste fluid? As far as I know I can only dump motor oil at the local auto parts places...
Your local recycling center should take it, or auto parts stores.
Also ask your local town or county government if they have an annual hazmat collection.
 

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I have a 2013 that has a P0128 code. I plan to replace the t-stat and housing, which I understand will require a top off of coolant. After researching the appropriate coolant, I uncovered the dreaded OAT/HOAT debacle, and since my JK was built in Nov. 2012, I'd rather just flush entirely and fill with OAT to be safe.

I did have my local dealer run my VIN, as well as Chrysler support online, both returning that I have OAT. I also pulled a sample from the radiator and determined it has the orange/pink/purple coloring. Likely I have OAT in there now, but I don't want to run the risk. Not for a few extra bucks and an afternoon of time.

So, my question is... I see most flush tutorials are simpler than the the OP's instructions. Whereas, the radiator is drained, the reservoir is drained and cleaned, and then using distilled water to cycle the water through the cooling system (running the Jeep with the heat on until the fan kicks in and the coolant/water is cycled). I understand this may take 6+ cycles using distilled water to fully return clean water and clear out any residual coolant. Is there anything wrong with this method? It seems simpler than removing a bunch of hoses, thus less likely that I will screw something up.

If pursuing this method, does it then make sense to fill the radiator and reservoir entirely with concentrate (not a 50/50 mix) as the rest of the system will be full with distilled water?

I appreciate any help!
 

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Discussion Starter #10
I have a 2013 that has a P0128 code. I plan to replace the t-stat and housing, which I understand will require a top off of coolant. After researching the appropriate coolant, I uncovered the dreaded OAT/HOAT debacle, and since my JK was built in Nov. 2012, I'd rather just flush entirely and fill with OAT to be safe.

I did have my local dealer run my VIN, as well as Chrysler support online, both returning that I have OAT. I also pulled a sample from the radiator and determined it has the orange/pink/purple coloring. Likely I have OAT in there now, but I don't want to run the risk. Not for a few extra bucks and an afternoon of time.

So, my question is... I see most flush tutorials are simpler than the the OP's instructions. Whereas, the radiator is drained, the reservoir is drained and cleaned, and then using distilled water to cycle the water through the cooling system (running the Jeep with the heat on until the fan kicks in and the coolant/water is cycled). I understand this may take 6+ cycles using distilled water to fully return clean water and clear out any residual coolant. Is there anything wrong with this method? It seems simpler than removing a bunch of hoses, thus less likely that I will screw something up.

If pursuing this method, does it then make sense to fill the radiator and reservoir entirely with concentrate (not a 50/50 mix) as the rest of the system will be full with distilled water?

I appreciate any help!
That's another way to do it, it does take more time. Not sure 6 cycles are necessary, maybe 3-4 cycles with distilled water should suffice. You'll end up with a lot of contaminated liquids to dispose of.
I think back flushing can better help remove sediments and gelled coolant.
I wouldn't fill with pure concentrate though, not that much distilled water would be left over after draining. Maybe use 70% OAT/30% water...
 

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That's another way to do it, it does take more time. Not sure 6 cycles are necessary, maybe 3-4 cycles with distilled water should suffice. You'll end up with a lot of contaminated liquids to dispose of.
I think back flushing can better help remove sediments and gelled coolant.
I wouldn't fill with pure concentrate though, not that much distilled water would be left over after draining. Maybe use 70% OAT/30% water...
Thanks. I'll probably take a stab at back flushing first. If I end up just cycling, I figured on my last cycle, after a fill with distilled, I can just subtract the amount I drain from the system capacity (10.5 qts.) to compute how much distilled is left in the system and add concentrate/water as needed.
 

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Discussion Starter #12
Thanks. I'll probably take a stab at back flushing first. If I end up just cycling, I figured on my last cycle, after a fill with distilled, I can just subtract the amount I drain from the system capacity (10.5 qts.) to compute how much distilled is left in the system and add concentrate/water as needed.
Speaking of 10.5 qt, I never was able to put in that much. Even after blowing air to flush water out of the heater core, oil intercooler and engine, it only took 8 qt to fill the system, whether cycling or final fill. Not sure where the rest was...
 

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Speaking of 10.5 qt, I never was able to put in that much. Even after blowing air to flush water out of the heater core, oil intercooler and engine, it only took 8 qt to fill the system, whether cycling or final fill. Not sure where the rest was...
Interesting. I'll keep that in mind this weekend when I do mine. Maybe the reservoir wasn't accounted for?

I'm in FL, so if my mix is a little higher with water, I won't be too worried.
 

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Interesting. I'll keep that in mind this weekend when I do mine. Maybe the reservoir wasn't accounted for?

I'm in FL, so if my mix is a little higher with water, I won't be too worried.
That includes the reservoir.

Does the 2014 Pentastar include water-cooled EGR? I'm not seeing obvious evidence of it but it's so crammed under there...

Since I did 2 "rinse cycles" with distilled water in addition to flushing with a garden hose, I put some a bit of pure concentrate in the reservoir to compensate for any pure water left over in the system - we can get below-zero temps here in winter.
 

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That includes the reservoir.

Does the 2014 Pentastar include water-cooled EGR? I'm not seeing obvious evidence of it but it's so crammed under there...

Since I did 2 "rinse cycles" with distilled water in addition to flushing with a garden hose, I put some a bit of pure concentrate in the reservoir to compensate for any pure water left over in the system - we can get below-zero temps here in winter.
I thought the EGR was a new addition for 2018 Pentastar's - not sure though.

I plan to to do a few rinse cycles as you did, so I'll just total the amount that goes in once the system is flushed (assuming it is actually flushed), and then subtract what I drain after the rinse from that amount and create as close to 50/50 as I can get. I think in this case 'close enough' is fine. I'll just plan to check the reso a little more often over the summer and top off with 50/50 as needed.
 

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Very complete write up! Thanks for taking the time to do it.:Thanx:
 

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Is there a way to connect a garden hose to the radiator fill and leave the petcock cracked open a tad to allow a constant, circulating flush for an hour or so? Then flush again with distilled then refill with fresh AF?
 

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The service manual mentions feeding water through the lower hose and letting it exit via the upper hose. You’d need to buy or fab some adapter.
 

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Does the 2014 Pentastar include water-cooled EGR?
I thought the EGR was a new addition for 2018 Pentastar's - not sure though.
The water-cooled EGR is only on the 2nd Generation Pentastar, that debuted in 2016 on WK2/WD.

2018 JK still had the 1st Gen 3.6 while 2018 JL received the 2nd Gen
 

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Wish I would have seen this post before but I did this last weekend and added a flush T to the left Heater Core hose to do complete back flush thru the heater core. After a good burping, the swooshing noise I had was gone and over heat issue resolved. Great write up!
 
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