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COOLANT BOILING

Yorgo52

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After engine is warm and then turned off after driving, coolant is boiling in overflow tank. Thermostat was just replaced but still happens. No coolant loss and no overheating on temp gauge. Car starts and runs fine. Interestingly, seems worse after driving up a long steep hill to get home. Fan appears to be working but could it be fan clutch? Or?
 
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Blackhawkxx

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Have you replaced the radiator cap? Is the antifreeze level in the overflow bottle higher when it is doing this?
 
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LorenzoGarbanzo

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Only times I've seen this happen - there was a blockage or an air pocket somewhere. Make sure the system is properly bled and that the engine isn't overheating.
 
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94Eddie

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Is the thermostat in backwards? Some thermostat designs can be reversed and fit perfectly.
 
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Mbrooks420

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If your coolant is boiling, you’re overheating. If you continue to drive it you’ll kill the motor (if it’s not already).
 
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ThunderbirdSport

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X2 on a possible air pocket. Also, how's the water pump? Definitely sounds like a flow issue. Like going up a hill, it gets hotter....it's not able to take the (extra) heat away. Gauges can be misleading too. Get a laser temp scanner and measure hoses, etc, just to be sure you're not actually running too hot.
 
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07EddyB

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Can you be more specific about the coolant 'boiling' in the recovery tank? Is it literally boiling like a pot of water on a stove? I've overheated mine briefly and believe me when I say the temperature and the cylinder cut out let me know pretty quickly. If you were getting that hot I would think you would see it on the gauge and in how it runs.
 
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prince402

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Check for a head gasket leak. The combustion gases can make it overflow and look like boiling. The fact that the coolant temperature is not too high points to this.
 
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Blackhawkxx

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Check for a head gasket leak. The combustion gases can make it overflow and look like boiling. The fact that the coolant temperature is not too high points to this.
I was thinking of the same thing as I had a Mustang that would fill the overflow bottle with coolant when I ran it hard. It had a bad head gasket that was leaking combustion pressure into the cooling system.
 
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Yorgo52

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Have you replaced the radiator cap? Is the antifreeze level in the overflow bottle higher when it is doing this?
I have ordered an OEM radiator cap. Should be here in a couple of days. It may be the best solution as I have noticed moisture coming out under the cap which would suggest pressure escape.
 
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Yorgo52

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Only times I've seen this happen - there was a blockage or an air pocket somewhere. Make sure the system is properly bled and that the engine isn't overheating.
Did bleed it. Didn't seem to be air in system.
 
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ThunderbirdSport

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When you say you seem to have moisture seeping from the cap, it makes me think you ought to do a pressure test on the cooling system.

I think the guy who suggested that combustion pressure is entering the cooling system may be onto something.

I hope this isn't the case because at best, you'd need new headgasket(s), or worst case, a cracked head or block...but a pressure test would point you in the direction of either that or a leaking radiator. Though the new cap is certainly a quick and cheap thing to try.

But I don't think a leaking cap is going to cause the boiling, or bubbling you're hearing. Keep us updated..
 
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94Eddie

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It is easy to check for hydrocarbons in the coolant. They sell kits for this at auto parts stores. Also, repair shops can do it quickly and for a decent price.
 
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Yorgo52

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UPDATE: Thank you everyone for your replies and suggestions. So the first thing I did was replace the thermostat but the issue was still there. I disconnected the rad hose and coolant came gushing out so I assumed water pump was ok. Fan was operating. No milky residue in oil so ruled out head gasket. I finally replaced the radiator cap, first time in 50 years of driving I have ever done so and guess what? Problem went away. So I think there was air getting into the system through a 15 year old radiator cap and what I thought was boiling was actually bubbling because of air. That's why temp gauge never showed overheating.
 
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94Eddie

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You might want to switch to a 16 psi cap. Some of us here think a lot of the radiator and other cooling system failures are due to the 20 psi pressure Ford has the system running from the factory. I changed mine a few months ago and see no difference in the cooling system's performance. After summer passes I will know if there is an issue running 16 psi in warmer weather. I keep the old 20 psi cap in the console just in case I need to reinstall it. My guess is I won't ever have to do this.
 
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Yorgo52

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You might want to switch to a 16 psi cap. Some of us here think a lot of the radiator and other cooling system failures are due to the 20 psi pressure Ford has the system running from the factory. I changed mine a few months ago and see no difference in the cooling system's performance. After summer passes I will know if there is an issue running 16 psi in warmer weather. I keep the old 20 psi cap in the console just in case I need to reinstall it. My guess is I won't ever have to do this.
Worth looking into. This vehicle is always in warm weather as I am in Puerto Vallarta, Mexico. Should I give it a try with 16psi?
 
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94Eddie

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Worth looking into. This vehicle is always in warm weather as I am in Puerto Vallarta, Mexico. Should I give it a try with 16psi?
I don't think you have anything to lose other than 4 psi of unnecessary additional coolant pressure stressing the cooling system for no good reason. Just keep the 20 psi cap handy in case you need to reinstall it.
 
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Yorgo52

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I don't think you have anything to lose other than 4 psi of unnecessary additional coolant pressure stressing the cooling system for no good reason. Just keep the 20 psi cap handy in case you need to reinstall it.
Thanks for the tip!
 
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Blackhawkxx

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UPDATE: Thank you everyone for your replies and suggestions. So the first thing I did was replace the thermostat but the issue was still there. I disconnected the rad hose and coolant came gushing out so I assumed water pump was ok. Fan was operating. No milky residue in oil so ruled out head gasket. I finally replaced the radiator cap, first time in 50 years of driving I have ever done so and guess what? Problem went away. So I think there was air getting into the system through a 15 year old radiator cap and what I thought was boiling was actually bubbling because of air. That's why temp gauge never showed overheating.
I'm glad that worked for you. Always start with the easiest thing.
 
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07EddyB

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So - the cap was stuck open? And that was letting air into the system although the recovery tank had fluid in it?
Am I the only one that thinks that victory has been declared prematurely unless pulling the hose while it was running shot something out?
Having a hard time wrapping my head around this one.
 
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