Flushing/Cleaning cooling system tips needed

99 xj, 4.0, aw4, 4x4

Since I have owned it (approx. 1000 miles) I have replaced the radiator, waterpump, thermostat, zj fan clutch, and did a coolant system cleaning using the Prestone cleaner and then repeatedly flushing with distilled water until everything was coming out clear.

Reason for all of this was a small leak in the radiator and extremely rusty coolant when I purchased it.

Recently I was towing a small utility trailer and I was running just above the 210 degree mark, probably around 215-220. When I parked, my wife noticed that I was dripping coolant and I popped the hood to find coolant boiling out of the overflow bottle. Once it cooled down, I popped off the radiator cap to find brown/rusty coolant again :scared:. So.... I need to do a thorough system cleaning/flush again.

Anyone have any tips/suggestions on methods or products?

Prestone works. It very well may take several runs of it before the sysstem is actually clean. I applaud your use of distilled water as that reduces the chance of scale buildup to zero. I am assuming that the antifreeze was also mixed with the distilled water.

When I first obtained the 98 it had cooling issue (What? An XJ?) which was just one of the reasons it was so cheap. It took three runs with prestone before it was finally clean. BTW, what came out of the Heep after the first cleaning run looked remarkably like india ink. Jet Black in colour.

You have changed everything. If I may ask, have you fitted a transmission cooler in front of the radiator? During my chase to install the Davies-Craig EWP115 electric water pump, I discovered that my transmission cooler (located in front of the radiator, mechanical fan side) was creating enough of a reduction in the air flow to cause a 5 degree Celsius increase in the operating temperature. After relocating the cooler to on top of the front skid, I gained the 5C back. IMO, if you can turn a problem on and off, at will, you have the solution in hand. I did have to drop the skid 3" so as to clear the sway bar... But then, what use is the factory skid on a lifted Heep? It sits way too high...

There are more agressive chemicals out there and there is a thread here somewhere that documents the use of one of them. However, they are very spendy. Coampare prices and see if it makes sense to go with the very agressive stuff or just run the (2 hour cycle?) Prestone a couple of times.

I can say that the "quick" flush cleaners are a waste of time and money.

Bjorn86 said:

Anyone have any tips/suggestions on methods or products?

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Tips:

Flush the heater core separately, and repeatedly. Backwards and forwards...did I say repeatedly.

Be sure you're getting ALL the old crap out. Pull the lower hose and the t-stat housing and just run water through the block and through the entire radiator. The actual flushing does not require distilled water IMHO, just the final 50/50 mix.

Thanks for the quick replies.

Yes, there is a small trans cooler (was there when I bought it) fitted along the bottom left (looking at front of vehicle) of the radiator, but doesn't block much of the radiator at all. And yes, antifreeze was mixed with distilled water also.

I will make sure to flush the heater core separately both ways.

I plan on cycling cleaners until it comes out clean, and then probably one more cycle just to make sure.

Also on order: new upper/lower radiator hoses, new radiator cap, and probably new heater hoses. All were re-used when I replaced everything else due to a lack of funds. The upper/lower hoses had a layer of rust in them and I tried to clean them up as much as possible.....maybe this could have led to contamination of my new coolant? I'm assuming the heater hoses look the same way.

Bjorn86 said:

I'm assuming the heater hoses look the same way.

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they are 2 different sizes.

3/4 and 5/8

Well, they could be 5/8 and 11/16...

I'll probably get knocked for this but I had bad luck with flushes. Couldn't get of all out for the life of me. I went to a pool supply and got some muriatic acid and ran it at 40 percent through the system. Thee was so much hunk that the petcock on the rad wouldn't even drain. I had to remove the lower rad hose to flush all the junk out. I did this twice to make sure I got it all out. I then flushed it with distilled water for 20 min then drained it. And finalized with a 60 40 coolant mix. No issues since

they are 2 different sizes.

3/4 and 5/8

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Well, they could be 5/8 and 11/16...

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Mine are stock, one is 5/8, the other is 11/16. From what I understand, 11/16 is hard to find and expensive. I'll probably do both in 5/8 and just use some type of lube and muscle to get it over the 11/16 fittings, as I have read that many have done.

Bjorn86 said:

I'll probably do both in 5/8 and just use some type of lube and muscle to get it over the 11/16 fittings, as I have read that many have done.

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I used a little dielectric grease to slip it it over the t stat fitting. Its what i had and it worked great!

The correct hoses aren't expensive. Gates 19038 and 19039.

bails85 said:

I'll probably get knocked for this but I had bad luck with flushes. Couldn't get of all out for the life of me. I went to a pool supply and got some muriatic acid and ran it at 40 percent through the system. Thee was so much hunk that the petcock on the rad wouldn't even drain. I had to remove the lower rad hose to flush all the junk out. I did this twice to make sure I got it all out. I then flushed it with distilled water for 20 min then drained it. And finalized with a 60 40 coolant mix. No issues since

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I never though about using Muriatic acid...good call. I had a heck of a time flushing my cooling system. The PO gobbed up the cooling system with Stop Leak. LOTS of it. The Prestone flush wasn't cutting it so a buddy of mine who's a Ford tech gave me a bottle of some heavy duty neutral Ph iron cleaner. It worked well.

bails85 said:

I'll probably get knocked for this but I had bad luck with flushes. Couldn't get of all out for the life of me. I went to a pool supply and got some muriatic acid and ran it at 40 percent through the system. Thee was so much hunk that the petcock on the rad wouldn't even drain. I had to remove the lower rad hose to flush all the junk out. I did this twice to make sure I got it all out. I then flushed it with distilled water for 20 min then drained it. And finalized with a 60 40 coolant mix. No issues since

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This is a joke right? That's some really nasty and highly reactive stuff. I could understand MAYBE using this to clean a radiator out (with it out of the car), but running that stuff through the block? I sometimes run sand in my intake to polish my valves lol

I personally don't know enough about muriatic acid to mess around with it, I will probably stick to a cleaner meant for cooling systems. I appreciate your input though.

As far as the hoses, the Gates hoses come in right around $25, whereas 8 feet of 5/8 heater hose is less than $10. The budget is tight right now, so I will probably take that route. I appreciate those part numbers though.

Bjorn86 said:

I personally don't know enough about muriatic acid to mess around with it, I will probably stick to a cleaner meant for cooling systems.

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Its some pretty aggressive stuff for sure. We used to use it on garage floors to prep for apoxy paint chip applications (only 12oz per 5 gal of water) to break down ANY thing on the concrete. And that too if not carefull. The only way i know to effectivly neutralize the stuff is ammonia. I sure as heck wouldn't be putting it in a cooling system.. JMO though. Best of luck for those that are.


Stick to the cleaners ment for cooling systems. If it doesn't do the job. Get a new raidiator, or have it professionally cleaned by a shop.

Bjorn86 said:

I personally don't know enough about muriatic acid to mess around with it, I will probably stick to a cleaner meant for cooling systems. I appreciate your input though.

As far as the hoses, the Gates hoses come in right around $25, whereas 8 feet of 5/8 heater hose is less than $10. The budget is tight right now, so I will probably take that route. I appreciate those part numbers though.

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All 4 hoses should cost you ~40 on www.rockauto.com and then ~3$ for new clamps at the hardware store. I would buy new gaskets for the water pump and thermostat housing, and a new themostat also and while your at it. Reason for this is just take the both of them off so you can just shove a garden hose in the block and go crazy.. at least that is what i did.

ktwalker01 said:

All 4 hoses should cost you ~40 on www.rockauto.com and then ~3$ for new clamps at the hardware store. I would buy new gaskets for the water pump and thermostat housing, and a new themostat also and while your at it. Reason for this is just take the both of them off so you can just shove a garden hose in the block and go crazy.. at least that is what i did.

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Thermostat is brand new, OEM Mopar 195 degree, has 1000 miles on it.

Way back in the day, we would drain the cooling system and fill it with vinegar. Yes, I said vinegar. The acid in the vinegar reacts with the mineral deposits and disolves them. n the positive side, what you have to drain out after the process is actually OK to just dump out as the vinegar has been neutralized by the base components it reacts to.

But your vehicle will smell a bit odd for a very long time.

Works though...

The hoses are "prebent" and are relativley inexpensive. Even the NAPA hoses are no more than $24 for the most expensive one... So, for basically the same price as rockauto, it appears you can drive to your local NAPA and snag both hoses. Shipping has to be factored in after all.

What you do not want to do is replace the 11/16 hose with the smaller 5/8 line. The reason the return hose is larger than the feed line to the heater core is to create a local pressure drop in the system to promote the coolant flow throught the core. The pressure drop aids fluid movement when the fluid gets to the suction side of the water pump.

Basic physics. If you take a finite amount of a working fluid, under pressure, and suddenly increase the volume it has to occupy, the pressure will drop. And, we need that pressure drop for the system to function properly or the Engineers at Jeep would not have bothered with creating hoses with differing IDs...

o-gauge-steamer said:

Way back in the day, we would drain the cooling system and fill it with vinegar. Yes, I said vinegar. The acid in the vinegar reacts with the mineral deposits and disolves them. n the positive side, what you have to drain out after the process is actually OK to just dump out as the vinegar has been neutralized by the base components it reacts to.

But your vehicle will smell a bit odd for a very long time.

Works though...

The hoses are "prebent" and are relativley inexpensive. Even the NAPA hoses are no more than $24 for the most expensive one... So, for basically the same price as rockauto, it appears you can drive to your local NAPA and snag both hoses. Shipping has to be factored in after all.

What you do not want to do is replace the 11/16 hose with the smaller 5/8 line. The reason the return hose is larger than the feed line to the heater core is to create a local pressure drop in the system to promote the coolant flow throught the core. The pressure drop aids fluid movement when the fluid gets to the suction side of the water pump.

Basic physics. If you take a finite amount of a working fluid, under pressure, and suddenly increase the volume it has to occupy, the pressure will drop. And, we need that pressure drop for the system to function properly or the Engineers at Jeep would not have bothered with creating hoses with differing IDs...

Click to expand...

How long did you run the vinegar for? I may give this a shot. I swear my wife makes all kinds of concoctions with vinegar, this will probably get her out to work on the XJ with me.

As far as the hoses go, ^ that info is greatly appreciated. I definitely don't want to decrease efficiency in any part of the cooling system.

What about adding this stuff after I do the flush? Anybody have input or experience with this?

http://napaonline.com/Catalog/CatalogItemDetail.aspx?R=MCR1300_0075099935

Thank god i'm lazy, i just drop it off at the rad shop and pick it up after they're done.Kinda nice to have it done and not worry about it.Last time it was done it cost me 90 bucks, they found a small leak and repaired it for me.