Radiator flush mishap question

As the title states I had a mishap while flushing my coolant system and I’d like to understand what happened so it doesn’t happen again.

I had to replace the heater control or water control valve, so I also replaced all the hoses on the firewall. That all went pretty well other than the difficulty getting those hoses off, that was tricky due to the tight space between the block and firewall. After having completed this project I’d recommend having some of those longer reach pliers for reaching down between the block and firewall.

Anyhow, everything was going well and I was on my third or fourth flush with distilled water. I was using one of those radiator funnels and was quite pleased with how well it had been working. My neighbor came over and started chatting with me and I wasn’t paying quite as much attention to the process as I should have been. I had the funnel in place and was letting it idle with occasional revving the engine to burp out the air, just as I had the previous times. Really the only difference I can think of was that this time it was taking longer than the previous times and I think the water was also hotter than any of the earlier flushes.

My neighbor’s wife called him in for dinner and as I looked back to the funnel I noticed the water level going up fast and it was about to spill out. I went to turn off the ignition as quick as I could, but the water spilled out a quart or so. In the moment I actually thought my radiator bought the farm.

I let it cool down and then added more water to top it off and waited to see if there were any leaks which I didn’t find. So I put the cap on and started it up. Everything seemed fine although I didn’t leave it running long enough to get too hot.

So my question is, what happened? I didn’t have this trouble any of the other times and other than being distracted by my neighbor and taking longer than the previous times nothing was really very different in my process. The instructions do mention not to over rev the motor, which I don’t believe I did. It states “excessive RMP can cause the fluid to erupt” And, “If fluid level should rise excessively shut down engine and wait for fluid level to lower before restarting engine”.

Any ideas or suggestions other than keep a closer eye on the fluid level and don’t dillydally? I’m assuming that since the instructions specifically state the fluid level can rise excessively that this is what happened, but I’d really like to make sure this doesn’t happen again especially with the coolant.

 

Sounds like a burp was comin thru. Did you hurt anything? No. Worried? Blow it off. Carry on.

 

Alright, I warmed it up to operating temperature and drove it around the block. Everything seems fine. I was pretty worried yesterday because I thought I heard a noise like something broke. But, I think it was just what the instructions warned about. I’m not sure if I over revved it or maybe I overstayed my welcome. I’m leaning towards overstaying my welcome since I was distracted and I’m fairly sure the length of time was the only real difference in my approach from the previous successful fills. I was actually past ready to shut it down and remove the funnel when I noticed the fluid level surging.

So don’t do either of those two things with a radiator funnel and you probably won’t have the mess on your hands I did.

Also, once the coolant system was filled and I was burping it, I was careful not to have more than about a third of the funnel full of fluid. I’d recommend doing this as well since it may allow extra time to get it shut off before an overflow.

Be prepared to shut it down quickly because it happened very abruptly. I’d make sure to have the window rolled down so you can reach the ignition as quick as possible.

 

The coolant molecules were excited from heat. Coolant does not steam off until a much higher temp than water. But it does still expand. That is why there is a coolant overflow reservoir.

Seems to me, based on your description that you let it get a little hotter than you usually do (in your procedure), and the radiator cap was not on, so it spilled instead of being pushed into the hose for the reservoir.

by the way, the system (if in good working order) will self burp air into the overflow tank when hot. As the system cools, it will suck fluid from the tank, into the radiator.

for small burps, you can just let this happen on its own.

 

Nope! It couldn’t be that easy.

Well, after fooling around with it for a bit yesterday, I think there may be a coolant circulation issue of some sort. I’m wondering if I might have a blockage somewhere or if the water pump could have failed.

Everything was working perfectly up and until the fluid eruption. The newest detail is the heat has completely stopped working - zero heat. I had been measuring the amount of coolant draining out and it was 5.5L the first time and 6L the second time. I didn’t measure it after the eruption because I thought everything was fine, but the last drain was only 4.7L. Somewhere between .7L to 1.3 L is not getting into the coolant system, which means I am only getting about 90% of the expected fluid into the system.

On the previous fills I was able to successfully purge at least most of the air out of the system and everything - including the heater - was working as expected. Because of this, I'm leaning against the idea it's the new water control valve, a defective thermostat, or air in the system, unless it is because of a blockage.

The drain right after the eruption did have a small amount of grey sludge in the bottom of the pan which didn’t happenon any of the other drains and made me think of the water pump, but there are no leaks or noise that I can tell. The sludge did remind me of the residue left behind when my power steering pump bearing bit the farm.

The eruption in the funnel continues to happen when I try to burp the air out of the system. I now seem to be unable to get the correct amount of fluid either into or out of the system. I pour as much fluid in as it will take and then start it. It starts off okay with some bubbles coming up. As it idles, the fluid level slowly begins to rise in the funnel as the engine is warming up. I made a mark on the funnel so I could easily monitor if it was rising to prevent another eruption. I also checked the overflow tank with the cap on and as it heats up it does begin to push fluid in there as well. It began dripping pretty quickly after I started it, but it was already warmed up a bit.

The radiator, thermostat and water pump are original. The inside of the radiator looked clean aside from some green stain/residue with no visible corrosion. The water pump isn't leaking or making any noise that I can tell. Other than the bit of grey sludge in the drain right after the eruption, there wasn’t anything in the pan after drains other than fluid. I did gravity flush the heater core via the inlet when I had the hoses off and nothing came out except coolant.

I’m a beginner mechanic, but I’ve learned quite a bit pretty much exclusively through this forum and youtube. I’m learning as I go and this is my first work on the coolant system. I need to figure out what is going on and would appreciate any help on how to go about it.

Any ideas appreciated? What do you think?

 

I think there's a lack of understanding here as to how the coolant system works.

When your truck is cold (<190*F or so), the thermostat is closed and fluid does not return to the radiator. When it reaches operating temp, it does. This is probably what the flood of fluid is - not air/burp.
Your coolant cap is pressure rated. This is so that the system becomes a closed loop system and releases fluid to your expansion tank if pressure becomes too great (typically due to temporary, excess heat, or having too much fluid in there in the first place).
After a coolant drain/refill, I have never let my cars run so long that it gets to the thermostat opening - you don't need to really burp anything imo, air will rise naturally to the highest point and it will be the first thing to be let out by the pressure cap.

As to your heater core, that would seem to be its own issue. Can you test the bypass flap by hand?

 

I think you're just overthinking it. The way you use those funnels is to never fill it more than an inch or two above the bottom (the taper line is a good target). You do the initial fill and let the system run until the thermostat opens and sucks the fluid down. Fill again until you have an inch or two and let it run a while until it stabilizes. As the coolant heats up and as it burps, the funnel will drain and fill itself as it's replacing the reservoir and this is fully expected behavior (also why you just barely fill the funnel). Just fill that little bit if it's drinking and leave it if the system is filling it.

The problem with revving the engine is that you get coolant moving, and depending on the system design, if there's a bottleneck downstream of the radiator, the fluid will back up into the funnel. At most you want to run it at a high idle and you want to be very consistent and deliberate - no blipping or dumping the throttle. Once you stop seeing air bubbles and the system is stable at operating temp, shut it down (yes, the level will probably rise) and let it sit a few before plugging the funnel and closing it up with the standard cap. Fill the reservoir to the max line and take it for a spin. You'll want to re-check after a few days while it's cold to confirm the level but doing it this way never failed me when I was wrenching.

If you're having a no-heat issue you are either dangerously low on coolant or there is a valve/obstruction issue. Make sure the coolant side is correct before chasing the valve/obstruction.

 

You have an air pocket in the cooling system. As the air pocket heats up it expands causing the coolant level in the funnel to rise. You need to rebleed the system. Make sure the heater is on full heat. I'd Rev it up hold it for 30 seconds then let it idle for a minute or 2. You'll find your heat comes back.

 

And park on an incline so the mouth of the radiator is the highest point in the system, so it's higher than the hoses and blend valve and all that stuff. Better chance of bleeding the air out, if their is any air. It can be a pain to get all of the air out sometimes.

 

Okay…..I have it figured out. It is an air lock at the heater core as was suggested. The recommended higher revving and massaging the heater hoses seems to get all the air out of there and then everything works as expected.

I think the fluid difference I noticed on a couple of occasions may have been due to having the control valve closed. I had been fooling around with it and I think leaving it closed is what led to less fluid on a few drains. When I leave it open I get the expected amount which makes sense.

I was reading some threads last night and I noticed I’m not the only who has had difficulty purging the air on the 2.7L, so maybe it is just fussy.

Thank you for the help, I appreciate it.

 

That's great to hear, hermano! Thanks for letting us know