To much build up pressure in coolant system!

Hey guys, I was driving to Carlisle from New York in my 72 slant 6 Dart. Went 100 miles and stopped for gas, but I got out and saw white smoke and coolant puking everywhere. Coolant overflow tank had a hole at the bottom. Checking that the radiator was not leaking (its not), I figured maybe the overflow needed to be replaced. Limped out to Napa and got coolant, overflow tank, and new radiator cap (vent was getting sticky and cap was hissing). Drove maybe 10 miles and checked it. No overflow anymore but a lot of hot hot hair pressure in the overflow. Thought it was doing okay so was driving towards home. Didn't go more than 20 miles before white smoke filled the cabin and under the hood and I heard a horrible noise. Pulled over and shut off the car immediately, while the noise continued. The overflow host blew off the radiator and sprayed hot coolant everywhere! Ended up getting my car towed to the end of a disappointing day. In questioning my 180 thermostat, by both it and my water pump are new as of last year. Pulled my oil dipstick but no milky oil. Help would be greatly appreciated!


EDIT: want to add that the idle got pretty rough a couple days before this, like a misfire during idle and under acceleration then a stumble under hard acceleration. When driving on the highway, I had a sudden loss of power for about 5 seconds where it was stumbling horribly and the throttle did not help. I finally mashed the pedal and it gained power. This happened before the coolant problem. I have good fuel delivery looking down the throat of the carb. The misfire is intermittent.

What did the temperature gauge show during all of this? Sounds like you overheated.

Cap failure could cause the overpressure, but it did the same thing with two different caps. Now, both caps could be bad or maybe the replacement was the wrong type, but that's a fairly big coincidence. The thermostat wouldn't have much to do with it, it either opens or doesn't. If there's hot water in the radiator then the thermostat is at least partially open. Same for the pump, it's would be impossible for it to create an overpressure by itself.

Did you run the system open (cap off) for a bit after you added coolant? The hot air in the overflow could have been at least partially because you didn't get all the air out of the system after you added coolant. But even then you shouldn't generate that kind of pressure. Did the new overflow container have a vent or way to drain if it filled up completely?

I'm going to go on record here and say Head gasket/ cracked head. Sounds like your getting compression into the radiator.

Looked at it a little more when it got home. Man did it stumble and misfire when I was backing up an incline to get into the driveway. Coolant was everywhere, so I rinsed most of it off with some water. And yes, my new overflow tank has a small hole at the top to relieve pressure. My dad revved it a couple times with it stumbling and popping, with white smoke coming out the tailpipe upon starting it up and deceleration. Trying to get the problem recreated but it wouldn't do it by just sitting there. Checked the temp of the fluid (no burps of air came out after 10 minutes) which was 185. Turned it off, checked the thermostat. It was open like it should have been. Checked the oil dipstick. May have been from the house down of the engine but there was some wetter bubbles on there. I'm fearing a broken head gasket/even a cracked head. My dad thinks we should look at the water pump next (that's also new, under a year old). Any other things to check to rule out broken head gasket?

Pull the plugs and check them for moisture. If you have the ability to put air in the cylinder, look for bubbles in the radiator with the cap off. Do this with the engine OFF! If not take a compression test. That should keep you busy for a while.

White smoke out the exhaust and pressure out the overflow nails it. You have a breach in the head gasket, head or block.

White smoke out the exhaust? With that info I'm with RRR, it's either the head gasket or a crack. If you have the equipment to do a cylinder leak down test that would be the next step, or a compression check as already mentioned. The leak down test would be a little more accurate in pinpointing the leak rather than just telling you the low cylinder(s), but at that point it's pretty moot as it all has to come apart anyway.

"with white smoke coming out the tailpipe upon starting it up and deceleration.' (Head gasket or cracked head) Coolant doesn't get in the combustion chamber unless you have a crack or gasket leak.

reenactment of Duel?

Looks like I'll be pulling the head then tomorrow to see what's going on! I'll post here again when I get a better look at everything.

Well I pulled the head! And it looks like for the first time on my engine by the looks of the stamped steel head gasket. Unfortunately though, I did not find an obvious problem that could have led to what happened a couple days ago. The head gasket is still very much intact. So, I'll show the pictures of what I got and what I found and hopefully I can find a conclusion. The head is going to the machine shop to get hot tanked and pressure tested for any cracks.



(Just to note here, the coolant in #4 I believe is what pour out from the head when we lifted it off). So here's the block and pistons. Typical carbon build up on the tops. From the passageways, the top triangular one in between #3 and #4 looked like a lot of hard crusty carbon build up, as well as the big circular passageways next to #6 and #1. Also on #2, there seems to be a pretty bad blockage of some sorts? You can see it better in the next picture. I tried looking close but I couldn't find any real cracks in between the cylinders or passageways. Then again, it is dirty so I will gently try to clean the surface to see if I can find anything.





Close up of the cylinder walls of #1-#3. Lots of varnish on the tops but I assume that's pretty normal? Other than that the cylinder walls look very clean. There's the "plugged passage" mentioned earlier on top of #2. What are those passageways for?



The cylinder head. There looks like there is some moisture on the exhaust valves? They were all pretty dry when I took the head off. Are the white exhaust valves normal engine operation? Again, I couldn't see any cracks but it is very dirty. This will be headed out to the machine shop to get cleaned up and tested. And just to put it out there, I've never really taken the head off an engine so I am not totally sure what is normal and what is not. If something looks abnormal then I can take a closer look.



The tops of #6-#3 for a closer look. Some buildup in the coolant passage of #3.



The head gasket. I think it's original because I saw a little pentastar on the bottom of it and it's stamped steel. No breaks anywhere on it, which only means the mystery to find something wrong only goes further.




The freeze plugs. Now this is where I found something a little abnormal. The day before the coolant blew out I noticed a very small leak coming from the second from the left plug. This was very new looking as I've never noticed a leak and it did not look like it was there for long at all. Now when I took the manifolds off, I noticed that it was not as flush as all the others, as a side of it was up a little more. It was also void of all paint and looked like it was getting pretty hot. Maybe from the exhaust manifold? I never noticed it like this before however. So I popped it out and it said it was an 'EZ' plug. The top was some sort of metal but the inside was rubber. Obviously these all but one are not the original brass freeze plugs. I intend to replace them but was this my problem? Or did it simply 'pop' out due to the excess pressure in my cooling system? Note how green the coolant is in the plug, because this is what I found in my overflow tank....




I also spun my water pump to see if it spun. It spun freely and sounded like it was moving what coolant was left in the block. I just replaced the water pump a little under a year ago, however I'm confused as to why i have such different colors in my coolant. Is there just a blockage somewhere? Still doesn't explain the white smoke out of the tailpipe though. I'll keep looking, I appreciate the help.

I am very suspicious of all the rubber core plugs. Almost like the block froze with not enough coolant in it. I hope there isn't a crack somewhere. If you're lucky it will be just a cracked head.

The rubber plugs are temporary fixes until real metal ones are installed. From the paint on them, it appears as a fix it and sell it.

Yeah, ditch the rubber plugs for sure. They suck. That "coolant" from the overflow certainly has oil in it.

Heading out today to get new manifold, head, thermostat, and valve cover gaskets, as well as brass freeze plugs. Should I use a sealant on those freeze plugs? Also want to flush out my radiator and block of all crud that may be in it. Would a garden hose do it or should I add something other than water?

I use Indian Head Shellac on all my freeze plugs before I install them. Yes flush the block as good as you can.

I popped all but one freeze plug off my block (the real freeze plug is being a pain to get out as it won't budge at all, I'd prefer to replace them all). Started to flush out the ports when I saw this passageway above #3 cylinder was waaay beyond clogged with crap. No way there was much of anything getting past that. Curiously enough that is also above where my problematic freeze plug was weeping a little coolant. On the head where that passageway met with another passageway that was the most clogged one with milky, gooey brown 'coolant'. I'll be taking a round wire brush to those to get them extra clean and continue to flush them all out. Machine shop tomorrow with the head! Oh, and I may have seen why my idle and driveability got so poor; pulling the spark plugs revealed they were in very poor shape with the amount of wet milk-chocolate brown buildup on especially #3 and #5. I could almost pull chunks off it was that bad. The head will be getting all new seals to fix that problem, providing that there's no cracks.

Milky, gooey, brown, Sounds like oil mixed with antifreeze or worse yet a system full of stop leak. Sounds even more like a block got froze and popped the core plugs out cracking the block or the head.

toolmanmike said:

Milky, gooey, brown, Sounds like oil mixed with antifreeze or worse yet a system full of stop leak. Sounds even more like a block got froze and popped the core plugs out cracking the block or the head.

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Well I do have to admit that when I pulled into the gas station and saw the coolant puking out for the first time, I thought my radiator busted because of the large wet area on it. (there is a pinhole leak that I need to fix; besides the point, it must have just gotten sprayed from the overflow tank and driving) Thought that was my problem and was 90 miles from home so I put it in there to just make it home. Turns out it wasn't the issue because it did the exact same thing in less than 4 miles of driving... Still, the coolant originally was a milky brown that I saw when it puked it all out of the leaky overflow tank I had. But when you say the "block got froze", you mean like ice frozen or seized?

Dodge72 said:

Well I do have to admit that when I pulled into the gas station and saw the coolant puking out for the first time, I thought my radiator busted because of the large wet area on it. (there is a pinhole leak that I need to fix; besides the point, it must have just gotten sprayed from the overflow tank and driving) Thought that was my problem and was 90 miles from home so I put it in there to just make it home. Turns out it wasn't the issue because it did the exact same thing in less than 4 miles of driving... Still, the coolant originally was a milky brown that I saw when it puked it all out of the leaky overflow tank I had. But when you say the "block got froze", you mean like ice frozen or seized?

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Lack of antifreeze and froze from the cold. If it freezes it will pop core plugs out (frost plugs) but can very easily crack the block or heads.

Those are core plugs, not freeze plugs, frost plugs or some kind of block protection scheme. Very rarely, IF at all did they actually prevent block damage from freezing. When the block mold is poured, you need an access point to get the core casting sand out. Picks, rapping, vibrators all were used to quickly get the sand out, then the holes machined for a water tight seal. Sure someone at sometime got lucky, it would be neater still where the "history" of freeze plugs started; but it's not their intent.

Been searching on Google again EH?

Been searching on Google again EH?

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Me? Are you talking to me?
No, it came from two sources; Fritz my Auto Shop instructor some 40 years ago, and employment at a foundry in Pa soon after.

As an FYI, one thing that has been going on is that the large irregular hole in the front of the head gasket is actually where the head gasket has corroded out. The original does not have a hole there; it is solid there to block coolant flow. When they have been in a car for 30-40 years, they corrode through there, and allow some of the coolant to bypass the head and block; most of it should flow to the back and the up through the 2 large holes in the back of the head gasket, so that most of the coolant flows through the length of the block front-to-back and then through the head back-to-front.

If I had to guess, I'd guess that is Bar's-Leak in the overflow, as suggested. It is pretty consistent and not quite like oil in the coolant. And there does not look like any coolant got into the crankcase, judging by the appearance of the lifter galleries. Drain the oil and check what comes out first.

It'll be interesting if the shop reports head warpage. BTW, what did the 'horrible noise' sound like?

If I may.
The entire green circled area is suspect, and the red is where the compression burn has been going.
The arrows point to water ports where the gasses were entering the cooling system, and quite possibly even the two big holes at the back of the block.
(Just forgot to circle those)
On the head the circled area is where it's burned the surface from getting past the gasket and gone into the water jacket on the upper side of the gasket.

It wouldn't surprise me one bit that this was all only caused by a really old head gasket failure, but of course it should all be checked.