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How to flush the cooling system on your Jeep Wrangler TJ

TJDave

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If you plan on overhauling your cooling system on your Jeep Wrangler TJ, one of the steps you should always take is to flush your cooling system. This is something that far too many people neglect to do, when in reality it should be done every several years at most.

Before you read any further, this is a thread worth reading: Jeep Wrangler TJ Cooling System Overhaul FAQ


What kind of coolant should I use?
In my opinion you should be using HOAT coolant in your Jeep Wrangler TJ. Hybrid Organic Acid Technology (HOAT) is a combination of IAT and OAT. Several manufacturers are using HOAT for their vehicles. One version is dyed orange and contains 10% recycled antifreeze. Another version is dyed yellow and does not contain any recycled antifreeze. Both of these HOAT antifreezes use the marketing designator of GO-5. They are compatible with each other but mixing them with IAT or OAT is not recommended. The normal HOAT antifreeze service life is 5 years or 150,000 miles (250,000 km).

A perfect example of a good HOAT coolant for use in your Jeep Wrangler TJ is the OE Mopar coolant. It may be a little pricier, but it's generally going to last longer and be better for your cooling system.


How much coolant should I use?
See this thread for fluid capacities (it varies depending on which model TJ you have): Jeep Wrangler TJ Fluid Capacities.


Supplies
  • 2 gallons OE Mopar coolant
  • 3 gallons distilled water
  • Large drain pan
  • 3 feet of 1.5" ID clear plastic tube (I think it was 1.5")

Drain Radiator

1. Make certain your engine is completely cool! Once it is cool, remove radiator cap.
2. Open radiator drain petcock and drain radiator into pan bucket or pan underneath vehicle.
3. Dump a gallon or so of distilled water through the radiator after is is done draining. Use enough so that you see nothing but clear fluid draining out.

View attachment 5111

View attachment 5112


Flush Heater Core

1. Found on the heater core inlet hose where I wanted the TEE fitting. Made 2 cuts removing a 3/4" section. This helps make up for the width of the TEE.
2. Use a funnel to put a gallon or less of distilled water through the hose.
3. Disconnected the heater core outlet hose and reverse flush the heater core.

Use the clear plastic tube to direct any coolant flushed from heater core hoses into drain pan.

Flush Engine Block

1. Look at the illustration below. Find your engine block coolant drain plug. Remove it and let the coolant drain into a bucket.

drain_plug.jpg



Finish With Heater Core Hoses
1. Install TEE in the already cut heater core inlet hose. Leave the cap off.
2. Reconnect the heater core outlet hose.


Clean Overfill Tank
1. Remove tank.
2. Clean tank.
3. Install tank.


Filling With Coolant
1. Added 5.25 quarts straight coolant to radiator. Topped off with distilled water.
2. Once coolant started coming out the TEE I screwed on its cap.
3. Filled coolant reservoir half way between Full and Add lines with premixed coolant/distilled water.
4. Started engine and let idle.
5. Squeezed the upper radiator hose a few times trying to expel any trapped air.
6. Made sure radiator was full of water and installed radiator cap. Instructions say to wait until you see water circulating before installing radiator cap. I didn't for some reason.
7. Ran engine for 20 minutes after it reached running temp.
8. Checked for leaks.
9. Stopped engine and let cool.
10. Checked coolant level and mixture ratio.

All Done!
Now wasn't that rewarding?
 

mrblaine

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Home Coolant Flush Report


My manual says to use HOAT coolant. After doing some research I got some Valvoline G-05 compatible coolant at Napa. My manual says my coolant system takes 10.5 quarts of fluid. So if I mix 50/50 I will use 5.25 quarts coolant and 5.25 quarts distilled water.

If you didn't drain the block, you have less than 50% coolant in there and more than 50% distilled water. After playing around with a couple of different coolant testers to find what the mix actually is after filling with a 50/50 mix after a flush, I've found that you need about 70% coolant to 30% distilled water to get to the correct ratio due to the dilution from the remaining water in the engine.

Drain Radiator

1. Put heater on high. Leave engine off.

4. Started engine and made sure heater is on all the way. Let idle.

The references to messing with the heater controls inside the rig make no difference. There is no coolant diversion valve in the system that alters how much coolant is circulating through the heater core. The difference in hot or cold air inside the cabin is controlled by the blend door on the air in the HVAC unit under the dash and not by changing the flow of hot coolant through the heater core.

If you look at the water pump, there are connections for the heater hoses and nothing else between them and the fire wall connections which are the two copper tubes that are attached to and direct the coolant through the heater core and back to the water pump.
 

MexiJeeper

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Nov 29, 2015
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Good write up. When I purchased my TJ in April 2014 I decided a coolant change would be a good idea. I had never heard of HOAT coolant before so on the hunt I went. Living in Mexico is a challenge as the items commonly available in the USA have never been heard of in Mexico. The only chain parts store I have seen is Auto Zone. I went there first. No HOAT. I then tried every other independent parts store in town with no luck. Finally went to the one Chrysler/Jeep dealer in Mazatlan and purchased it there....at 4 times the US price!

Oh and the simple backflush kit was not available here either. I had a visiting friend bring me one from California where every parts store has them.
 

RaymondT

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If you have a bench grinder and a simple dial caliper, you can easily make a block drain tool out of an old/cheap 3/8 socket extention. The factory installed a plug with a square 8mm hole which works out to .315". I don't think it took me even 5 minutes to make mine. Then you can easily pop out the plug as often as you want during flushing.

http://www3.telus.net/r_lowe/Drain plug tool 001 (Small).JPG
 

Stinger

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If you have a bench grinder and a simple dial caliper, you can easily make a block drain tool out of an old/cheap 3/8 socket extention. The factory installed a plug with a square 8mm hole which works out to .315". I don't think it took me even 5 minutes to make mine. Then you can easily pop out the plug as often as you want during flushing.

http://www3.telus.net/r_lowe/Drain plug tool 001 (Small).JPG


Great another tool to make/buy. Got to be close to the same thing for my engine!:rolleyes:
 
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RaymondT

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If you do decide to drain the block, pop out the temp sensor on the thermostat housing. Pour your coolant mixture into the rad until it starts to burble out the hole for the sensor. Then slap it in, connect the pigtail, and finish topping up the rad.

Removing this sensor allows the block to fill without the system air-locking. It helps to pre-treat the threads of the sensor with pipe thread sealant before you start pouring so it's ready to go.
 

CRGR

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If I take my baby to a Jeep mechanic and ask for a coolant flush are they going to typically do all these steps? I just feel like they'd half ass it.
I agree that they probably wouldn't take the time and effort to do it like this. That's what I love about being able to do stuff like this on my own. I'm by no means a mechanic - far from it - so write ups like this are invaluable.
 
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mrblaine

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If I take my baby to a Jeep mechanic and ask for a coolant flush are they going to typically do all these steps? I just feel like they'd half ass it.
Depends on how much you want to spend. If you want that work done for 50 bucks, probably not going to get the full thing. If you want to pay what it's worth, you're chances of getting what you want just improved a bunch.

Just to help you with the time frame, when we do a flush for a radiator swap, it takes a couple of hours to get the heater core back flushed and get the block cleaned out and flushed with distilled water. Then it takes a bit more time to get the new coolant and thermostat in, bring it up to temp to check for leaks and then test drive it to make sure it is all working correctly.

For us it is a minimum of 3 hours to get it all done.
 

CRGR

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Depends on how much you want to spend. If you want that work done for 50 bucks, probably not going to get the full thing. If you want to pay what it's worth, you're chances of getting what you want just improved a bunch.

Just to help you with the time frame, when we do a flush for a radiator swap, it takes a couple of hours to get the heater core back flushed and get the block cleaned out and flushed with distilled water. Then it takes a bit more time to get the new coolant and thermostat in, bring it up to temp to check for leaks and then test drive it to make sure it is all working correctly.

For us it is a minimum of 3 hours to get it all done.
What's a general $$ for getting it done right? Thanks
 

mrblaine

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What's a general $$ for getting it done right? Thanks
I have no idea. We do it as part of a cooling system repair so we are into the mechanical side of things anyway. We pull the thermostat first, put the housing back on, do the flush until the water is clear, flush that out with distilled, pull the heater core hoses and start flushing it both directions.

This is all after we've had the owner put in the Prestone slow flush and drive stuff so the system is ready to be cleaned out. Sometimes the heater core is clean, sometimes we put a stronger version of the Prestone in it and let it sit overnight if is looks like the flow is restricted. That requires strapping the hoses up and filling one until the mix comes out the other one and walking away for awhile.
 
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Gerund

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Know this is an old thread, but figured this was the best place for these questions.

Are you capturing all of what you drain?

How do you dispose of what you captured?
 

Chris

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Know this is an old thread, but figured this was the best place for these questions.

Are you capturing all of what you drain?

How do you dispose of what you captured?

Yes, I would capture all of it you can with a drain pan underneath. Transfer what gets caught in the drain pan to empty milk jugs and leave it with your recycling bin. The recycling people will take it, as long as it's just coolant in the milk jug. They won't take it for instance if it's coolant and oil mixed, but coolant / water mixed they will take.
 

Altonymous

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@Chris

Am I correct in that the drain plug for the block is right behind the rear pre-cat on the 4.0L (I have a 2005 LJR)? It seems to be .. but it's really hard to see. Can I remove it with a 3/8" socket wrench? I can barely get my eyes on it, but I can touch it with my fingers.
 
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Bratch

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This is all after we've had the owner put in the Prestone slow flush and drive stuff so the system is ready to be cleaned out. Sometimes the heater core is clean, sometimes we put a stronger version of the Prestone in it and let it sit overnight if is looks like the flow is restricted. That requires strapping the hoses up and filling one until the mix comes out the other one and walking away for awhile.

I’m getting ready to swap my radiator and am gathering supplies and information.

Is the Prestone slow flush a specific product? I checked their site and all I saw was the “Flush+Cleaner”.
 

mrblaine

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I’m getting ready to swap my radiator and am gathering supplies and information.

Is the Prestone slow flush a specific product? I checked their site and all I saw was the “Flush+Cleaner”.
No, not specific, it is the one you found. I call it slow because there are fast flushes that you can't leave in for 3 days or so while you drive around.
 

jazngab

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In preparation to overhaul the cooling system, I just completed a full flush. I’ll say that I almost half assed the flush but glad I didn’t. I disconnected the heater core hoses and ran distilled water through it. Not much residual water nor was it very dirty. I drained the engine block and must say there was a fair amount of fluid dumped out. I ran distilled through the outlet heater hose and flushed out through the engine block drain. I recommend doing the entire flush if you want to truly clean it out. I found while removing the thermostat housing it was corroded and there was sand and debris in it. So even if flushed it might be wise to update the whole system if it hasn’t been done.