Overheating and bubbling after turn off

[70Broncoboy]

I have been experiencing an issue where my Broncos coolant bubbles after turning the bronco off. Anyone have any experience with a similar issue and how did you resolve it?


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[Broncobowsher]

Define coolant bubbles? spitting coolant on the ground? Hear gurgling in the cooling system? Clear hose from the radoator to the catch tank shows bubbles? Lots of possible inturpatitions of what you ask.

Do you have a good radiator cap? One that actually holds pressure?

What you are finding is heat soak. Just because the coolant is 180 degrees, or whatever it is running at, doesn't mean everything in the engine is that cool. Heat transfer requires something to be hotter for the heat to transfer into something cooler. The coolant is the coolest thing in the engine. Everything else is hotter and putting heat into the coolant. Now stop the coolant flow. But there are still hot parts in the engine, and they are dumping heat into the coolant. As the coolant tries to boil the pressure rises. A good cap will hold that pressure, raise the boiling point and not get into a boil. A weak or non-sealing radiator cap won't hold pressure and coolant will boil sooner.

 

[Yeller]

@Broncobowsher is correct. The system is not holding pressure, and is probably the cap.

 

[Timmy390]

Good advice above BUT........WELL yes.....I had this issue with my freshly built 351W. https://classicbroncos.com/forums/t...lant-reservoir-on-my-fresh-351w-build.266011/

I'll save you the trouble reading Cracked head........

At idle no bubbles but when driving there were. After shutdown.......BUBBLES......That's how I found the issue. Walked by and heard the bubbling after I parked.

Tim

 

[ntsqd]

I've come to learn that radiator caps are not a one-time purchase either. They have a life-span and at the end of that life-span the engine starts running warmer than normal. I went thru several of them in the ~125k miles that I drove Patch. If something is starting to run warmer than it used to the first thing that I do is replace the cap.

 

[DirtDonk]

The interesting thing this says to me, at least, is that, in my opinion anyway, a bad or loose cap should not allow the engine to run hotter. The pressure simply changes the temperature at which the coolant boils. Not the ability of the coolant to transfer heat.
However, and this is a big HOWEVER(!), that also tells me that the extra pressure allowed by a good working cap, also is doing what we’ve talked about in the past. And that is keeping the coolant in better contact with all the inner surfaces of the engine block and cylinder heads. As well as keeping hotspots to a minimum which in themselves cause small boiling points, adding air to the system and promoting cavitation and hurting the overall efficiency.
More ambient pressure (cap) is good and more water pressure (pump) is good.
At least that’s what it says to me when a leaky cap causes the temperature to go up.

Probably not wording that, or using the words correctly. Hopefully everybody gets what I’m trying to say.

 

[70Broncoboy]

The radiator will not bubble on start up or while the motors running at a high rpm. It only does it while it’s off. I’ve put on three new caps and still am running into the same issues.


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[ntsqd]

Did it not do this in the past with the same radiator?

Have you done a coolant system pressure check?

 

[lars]

The radiator will not bubble on start up or while the motors running at a high rpm. It only does it while it’s off. I’ve put on three new caps and still am running into the same issues.


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Photos are worth many thousands of words.

 

[Chiclassics]

How do you know it is bubbling ? are you observing it without radiator cap to test any trapped air? explain your mechanism to see bubbling

 

[70Broncoboy]

How do you know it is bubbling ? are you observing it without radiator cap to test any trapped air? explain your mechanism to see bubbling

I have it plugged into an overflow bottle and when I’m trying to bleed the system of air it does it as well.


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[ba123]

I had this happen with a bad cap and I also had after refilling and not getting all the air out of the system.

Both reasons were air in the system where it should not have been.

 

[70Broncoboy]

I had this happen with a bad cap and I also had after refilling and not getting all the air out of the system.

Both reasons were air in the system where it should not have been.

I’m two new caps in with the same issue and 6 fill attempts with the same issue.


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[DirtDonk]

What is the coolant temperature during all this?
What you’re describing sounds pretty normal to me.
But as was asked, did it do this before? Is the Bronco new to you and you’re trying to track down this potential issue? Or did it just start, either out of the blue, or after some work was done?

 

[Chiclassics]

Post some pics. Its normal for coolant to bubble and overflow especially if its a rebuild new engine - not sure what your engine history is. As parts break in they produce a lot more heat during break in. If its just normal coolant overflow after you shut off engine its fine. Typically when I flush radiator and fill new coolant I keep radiator cap off for first 15mins to bleed any air out as it circulates (without radiator cap) and then shutoff engine and put radiator cap back on. You might have either trapped air or a in there in either case let it out.

 

[73azbronco]

I'd pressure test cooling system then report bak

 

[Brush Hog]

I found that if I filled my radiator up too much it would gurgle and spit all over when I turned engine off. Even with over flow bottle attached it seemed like it couldn’t or wouldn’t keep up. Once I stopped topping it off and keep the level to where the internal core is just barely covered with coolant when cold the problem went away and the over flow works perfectly. Engines temp stays constant 195-205 depending on outside temp.

 

[MarsChariot]

A small leak somewhere in the system, even a hose not quite clamped right, will keep the system from pressurizing. Lower pressure = lower boiling point. Our 76 was doing this the past year due to a leak on the side tanks of the radiator. New radiator (and cap) and problem solved.