Issues flushing dirty coolant

[SurplusFan98]

Recently rescued a 98 2wd 4.0 5speed XJ. After working through issues getting it started and running, I'm trying to flush out the cooling system.

Its hard to know how long this car sat up, and when I received it, the cooling system wasn't completely full. I could see that the coolant that was in it was brown (though not the worst I've seen) and there was some visible sediment under the rad cap. I went about flushing the system with as water hose, and I got all the old brown coolant out. I then reconnected everything and dumped in some rad cleaner and started filling with distilled water. Got it filled to the top and burped via the upper hose, and then started the engine. With the heater running full blast, I kept topping with water and burping until the radiator would not accept any more water, and then waited for the thermostat to open.

When the engine eventually gets warm, and right about the time I would expect the thermostat to open, the water starts essentially boiling back out of the radiator rather than sucking up any more water. The volume of stuff coming back out the way it went in eventually gets to be so much that I have to shut the engine off. The water coming back out is pretty brown and gross. I checked all the hoses, and they're all hot except for the upper rad hose by the battery. That seems to indicate that the thermostat doesn't open, but I'm not sure if that means its bad or if I'm just not patient enough.

So, my questions:

• Am I doing this right?
• Do I have a stuck closed thermostat, or am I just not waiting long enough for it to open (should I have put the rad cap back on and let the resevoir fill until it opened)?
• Is it possible that I just have a clogged radiator or hose?

 

[Saudade]

Have you checked compression on the engine?

What was the reading on the temp gauge when this happened?

If the thermostat is closed, very little if any coolant circulates to the radiator. The cool upper hose verifies that. Once the thermo opens, the heated coolant plus any trapped air can now escape into the rad. Some bubbling is expected as the air purges out. Since you topped off the rad, the purged air can eject quite a bit of fluid as it gushes out.

You may have to repeat the flush a few times. I always remove my lower rad hose to drain, and then flush the rad with my garden hose in the upper to really flush it out. I disconnect the heater hoses and flush the core in both directions as well. Be careful. DO NOT USE FULL WATER PRESSURE on the core.

So I don't think it's stuck closed. You wouldn't get "boil over" since everything would still be trapped in the block. The engine would over heat though and may stall.

It's not stuck open and just overheating since the upper hose is cool.

So it's possible the rad is clogged. I asked about the compression check to rule out a head gasket leak which can also show as bubbling in the cooling system.

 

[SurplusFan98]

Have you checked compression on the engine?

No, I haven't as I don't have a compression tester. I've experienced what you're describing before in my son's jeep, and I don't think that's what this is. The engine will run for a good 7-10 minutes and warm up from cold before I start getting anything bubbling back up from the rad neck. If I had a blown head gasket I wouldn't think it would take that long to build up air pressure and start seeing bubbles. What does happen is that when the engine finally gets warm, the water starts pushing back up through the neck pretty much all at once. The water coming out is definitely dirty, but not really milky or oily, and the oil isn't milky either.

What was the reading on the temp gauge when this happened?

That's another issue: I don't have a temp gauge. This is one of the Sport models that just has a temp warning light, and AFAIK it's never come on.

If the thermostat is closed, very little if any coolant circulates to the radiator. The cool upper hose verifies that. Once the thermo opens, the heated coolant plus any trapped air can now escape into the rad. Some bubbling is expected as the air purges out. Since you topped off the rad, the purged air can eject quite a bit of fluid as it gushes out.

OK, let me see if I got this straight. So what you're saying is that I fill the radiator which the water pump pulls from via the lower hose to fill the block. Then when the t-stat opens, the hot water from the block flows back into the radiator via the upper hose. If that's correct, why then doesn't that indicate a stuck closed thermostat? Not calling you out in any way, just trying to understand.

You may have to repeat the flush a few times. I always remove my lower rad hose to drain, and then flush the rad with my garden hose in the upper to really flush it out. I disconnect the heater hoses and flush the core in both directions as well. Be careful. DO NOT USE FULL WATER PRESSURE on the core.

Yep, did both of those things. I got pretty good flow from the upper to the lower hose via the radiator when I flushed it too. I understand my heater core may still be dirty, but my heat inside works great, and even if it was clogged I'm not sure that issue would result in what I'm describing, right (because the heater core flowing or not flowing wouldn't effect the circulation of the coolant through the radiator)? Not opposed to doing this repeatedly until its fixed, but I'm trying to make sure I know what "fixed" looks like.

So I don't think it's stuck closed. You wouldn't get "boil over" since everything would still be trapped in the block. The engine would over heat though and may stall.

This is where I'm confused. The engine gets hot and the rad cap is open. Couldn't expanding hot water come back up through the rad neck from either direction if the flow was obstructed? I realize that if my understanding of how the cooling system flows is correct, then all my heat is getting generated on the other side of the water pump. But if its getting hot and not flowing, wouldn't it still expand and eventually back up through the rad neck? Doesn't seem like its got anywhere else to go (except maybe through the head gasket).

Thanks for the response buddy. Just be patient with me. I'm trying not to be a parts canon guy...

 

[Saudade]

No worries!

What I meant by "not stuck closed" is you would not likely get any flow back to the radiator. The engine would overheat and likely stall. Sounds like the thermostat is opening, hence the rush of air and coolant after the warmup. If in doubt, remove the thermostat (once everything cools) and drop in some boiling water.

Since you don't have a temp gauge, you should get one of those IR thermometers and check the thermostat housing's temp.

Your scenario is certainly possible. Testing the thermostat should be next.

 

[RCP Phx]

Water is always flowing thru system even when the stat is closed. It flows thru the heater core since a '98 doesnt have a heater control valve!

 

[SurplusFan98]

Update: pretty sure it was the thermostat...

To check my suspicions, I drained everything and pulled out the thermostat. It was crusty, but still moved freely, though I still don't know at what temperatire it would have done so voluntarily. I decided that before I put another one in it I'd make a cereal box gasket and bolt the housing back on without the thermostat installed. I filled everything back up with some coolant flush stuff and distilled water. I then started the jeep and burped the system, capped the radiator and turned the heater up all the way. She ran that way for at least 30 minutes without overheating, and my upper hose was plenty hot this time. Now I'll just have to drain it again and install my thermostat and some coolant, and I suspect I'll be good to go.

I bought a failsafe thermostat this time. I love these things, but overheating issues are just the worst.

 

[SurplusFan98]

How many times are you guys having to flush a system thats been sitting up a few years? I'm using the Prestone stuff and distilled water, and letting the engine run for 30m to an hour. I back-flush the heater core between flushe cycles. I think I'm on flush #4. What's coming out still looks like toilet water. I'd think that was a good thing, so long as it gets better eventually...

 

[maxbraketorque]

How many times are you guys having to flush a system thats been sitting up a few years? I'm using the Prestone stuff and distilled water, and letting the engine run for 30m to an hour. I back-flush the heater core between flushe cycles. I think I'm on flush #4. What's coming out still looks like toilet water. I'd think that was a good thing, so long as it gets better eventually...

Are you pulling the lower radiator hose or the block drain?

 

[TheXJDrew]

With a vehicle that’s been sitting for a decent time, it can take a number of flushes to get all the bad coolant out. It wouldn’t even hurt to replace the cooling system if you’re able to, just to eliminate all the problems that could arise due to old nasty coolant. Coolant that has been sitting for a while can take a toll on a water pump as well. It’s not uncommon to see one that’s deteriorated due to not being used and coolant not circulating.

Side note, just a piece of advice, I have a couple of these funnels, one at work and one at home. They are an absolute life saver when burping a cooling system. They allow it to get to operating temp, the thermostat open up and burp the air out. They’ve worked wonders for me for years and help keep the mess to a minimum. I always use them, especially on Inline 6’s because they like to trap air in the back of the engine. It would be a good thing to use once you get all the nasty crud out and are ready to fill it for the last time and want to make sure all the air is out of the system.

https://www.amazon.com/OEMTOOLS-870...ocphy=9013464&hvtargid=pla-493792710903&psc=1

 

[SurplusFan98]

Are you pulling the lower radiator hose or the block drain?

The lower rad hose. I've actually encountered advice from different places that basically say to NEVER mess with the block drain unless you're doing a rebuild. Basically that you could strip it out and end up causing yourself a whole world of issues, you didn't have already.

Opinions?

 

[SurplusFan98]

With a vehicle that’s been sitting for a decent time, it can take a number of flushes to get all the bad coolant out. It wouldn’t even hurt to replace the cooling system if you’re able to, just to eliminate all the problems that could arise due to old nasty coolant. Coolant that has been sitting for a while can take a toll on a water pump as well. It’s not uncommon to see one that’s deteriorated due to not being used and coolant not circulating.

Side note, just a piece of advice, I have a couple of these funnels, one at work and one at home. They are an absolute life saver when burping a cooling system. They allow it to get to operating temp, the thermostat open up and burp the air out. They’ve worked wonders for me for years and help keep the mess to a minimum. I always use them, especially on Inline 6’s because they like to trap air in the back of the engine. It would be a good thing to use once you get all the nasty crud out and are ready to fill it for the last time and want to make sure all the air is out of the system.

https://www.amazon.com/OEMTOOLS-870...ocphy=9013464&hvtargid=pla-493792710903&psc=1

Thank you, these are great suggestions. Since everything is flowing and I'm not getting any overheating at idle now, I'm just going to continue to flush. At around $10 a flush, I can do a bunch before I've spent the money for a new radiator. Its also possible that the majority of the junk is coming from the head/block, in whichd case all new cooling components wouldn't solve the problem anyway. Its a good suggestion though. The funnels is too. I was aware of these but have been putting off getting one because I didn't think I would need it (and have been correct up until now). This job is swaying me. For $20, I'll likely get one.

I isolated and back-flushed the heater core a few times until its running clear, so I know that's not my issue. I had a way to bypass it, so I have. My next couple of flushes should only be getting junk from the head/block, water pump, or the radiator. If they don't clear up soon, I'll pull the water pump and look at it.

 

[maxbraketorque]

The funnel kits are awesome. I can't imagine working on a cooling system without one, at least if a goal is not to get coolant and water all over the place.

Are you using any of the rust/scale remover additives?

 

[RCP Phx]

White vinegar is a cheap good flushing mixture followed by a baking soda flush to neutralize everything.

 

[SurplusFan98]

Are you using any of the rust/scale remover additives?

Yep, using this Prestone Radiator Flush.

The instructions say to do a flush, and then refill with only water and flush. That was my original plan until what came out was essentially chocolate milk. Figured I might need a few rounds, and this stuff is pretty cheap (I actually buy it at Walmart). I've done at least 2 flushes with a full bottle, maybe 3. I just started doing them with a half bottle. I'm going to keep tapering off like that until what comes out isn't completely opaque. Then I'll do a water only flush.

Unless there are other suggestions...

 

[SurplusFan98]

White vinegar is a cheap good flushing mixture followed by a baking soda flush to neutralize everything.

That makes sense. Don't know why I didn't think of that. Thanks!

 

[75SV1]

I had the same issue on my '00. I did several flushes. For several weeks. It was early spring so I could not leave the flush in there over night. I did try vinegar. I would look at Blue Devil radiator flush. Also, saw something on NAPA's shelf today. What I have tried in the past is Citric acid. You would need a pound of it. Wine making shops will have it. Mercedes Benz used to or still does sell it. Also, after that flush, I ran a water mixture of baking soda to neutralize the acid. And then flush with clear water a few times. I used distilled water, as IN has a PH of 23. Mine still burped out crud for some months or so. Also, I made a "U" bend and took the heater core out of the loop. I also took off the water pump a few times and hosed water through the block. The rear of the block can get crudded up. I would wonder about putting a presser washer tip back there and blast away. Good luck.

 

[XJI6191]

A lb of citric acid, we can only get it in 50g pots & if you tried to buy more than couple (say to descale a coffee machine) they'd probably refuse, if they didn't call the police, 'cos you'd straight'way be marked down as a drug dealer (for any innocents abroad, it's a favourite cutting agent for cocaine)

 

[75SV1]

Seems you can order it over the net:
https://www.soapgoods.com/citric-acid-p-557.html?msclkid=6a74ef93d9331a05f5848b513cd92b45

CVS, Walmart, Kroger might carry it.

 

[maxbraketorque]

Seems like vinegar is a pretty common approach, but I'd be cautious about it.
The low pH induced by putting vinegar in the water causes metals to become soluble in water. Metal erosion rates increase dramatically when dropping into this regime. Not a big deal for a thick steel block or head, but can be a problem for an aluminum radiator or heater core if the pH is below 4. You could purchase some pH strips and see

I'd be more inclined to use Thermocure perhaps altering with the Prestone product. Thermocure attacks rust without lowering pH while the Prestone product works more on scale.

Anyhow, if you are using the Prestone, I'm not sure you should be expecting the coolant to ever be clear or nearly clear at the end of an exposure cycle. It may take hundreds of hours of exposures and flushed before the water is clear at the end of a cycle.

 

[75SV1]

I did have issues with the MB 240D radiator a year or so after the Citric Acid flush. Still, the brass radiator was over 20 years old.
I also tried Evapo Rusts radiator flush. That and the top end Blue Devil are suppose to be run for 3 days or more. I didn't give either that time, and there was possible freezing temps during the night at the time.