Is it normal for coolant to boil?

[Dark Lord]

I did some reading through a few threads and can't really find a definitive answer on this. I've experienced the weirdest shit on my 4runner recently.

About 4 weeks ago I was driving, and my truck started overheating out of the blue, with white smoke coming out of the hood, so I pulled over and popped the hood. The white smoke was coming from the coolant reservoir which was popped open for some reason. I look in my coolant reservoir (which was really low) and the water was boiling. I looked in my radiator and the coolant was all gone. I filled it back up with coolant, everything was fine ever since. I talked to a few people, and although this sounds weird the best explanation we came up with was that the water evaporated..... I checked the hoses and everything else and didn't find any leaks.

Well yesterday when I got home, I got out of my truck and heard a hissing under the hood. I looked at the coolant reservoir and the coolant was boiling. It was filled pretty high because when I looked in my radiator, it appeared all the coolant was pulled to the reservoir. I let it sit for a while, and when I came back the coolant was back in the radiator. I did notice some crusty pink stuff appeared to have spilled out of the radiator cap, and a couple drops were sitting in other places, but it didn't make a mess or anything. I went to Advance Auto and bought a new radiator cap, and everything appears to be running fine. What the hell is going on????

 

[morbidsanity]

well a it is running through a 200 degree engine....i believe water boils at about 140, when it boils at operating temp in the radiator it builds up steam and a light pressure, wich if your lid wasnt on correctly it prob shot off and blowing your coolant out....my 2 cents...

 

[Dark Lord]

I have antifreeze in there now, and that's what was boiling. Although I do believe some water is still left over, would it still boil like that? I thought antifreeze had antifreeze and antiboil properties or something.

 

[Kurtis]

Water doesn't boil until 212 degrees. I'm not sure what coolant boils at. I think some where around 245 degrees. Were you over heating when this happened yesterday?

 

[morbidsanity]

I have antifreeze in there now, and that's what was boiling. Although I do believe some water is still left over, would it still boil like that? I thought antifreeze had antifreeze and antiboil properties or something.

im not sure about anti boil but i do know that it is slightly pressurized from the heat....

 

[Dous]

When the water is pressurized the boiling point is even higher than 212. So it could be that your cap is bad and the coolant isn't pressurizing resulting in the coolant boiling.

 

[Skidmarcx]

When the water is pressurized the boiling point is even higher than 212. So it could be that your cap is bad and the coolant isn't pressurizing resulting in the coolant boiling.

This

 

[Dark Lord]

Water doesn't boil until 212 degrees. I'm not sure what coolant boils at. I think some where around 245 degrees. Were you over heating when this happened yesterday?

I was not overheating yesterday when this happened. I just got out of my truck and heard the noise and decided to take a look.

When the water is pressurized the boiling point is even higher than 212. So it could be that your cap is bad and the coolant isn't pressurizing resulting in the coolant boiling.

Thanks. I bought a new cap yesterday, we'll see what happens.

 

[JohnsD90]

I was not overheating yesterday when this happened. I just got out of my truck and heard the noise and decided to take a look.



Thanks. I bought a new cap yesterday, we'll see what happens.

He's referring to the radiator cap, I don't know what you bought, just giving a heads up.

 

[Dous]

I was not overheating yesterday when this happened. I just got out of my truck and heard the noise and decided to take a look.



Thanks. I bought a new cap yesterday, we'll see what happens.

Right, running 212 degrees wouldn't cause the stock gauge to read even a bit higher than normal, even though it is hotter than the working temperature....not harmful though.

So, what I am trying to say is, your cap is probably bad which is allowing not pressure in the radiator causing the water to boil at 212 which would not normally happen.

 

[shep0101]

Mine was doing the same thing and started bubbling just in the overflow. But now there is something dark coming out of the hose into the radiator over flow. Anyone know that this means, I just know its not good.

 

[JRZEE2000TR4LTD]

Mine was doing the same thing and started bubbling just in the overflow. But now there is something dark coming out of the hose into the radiator over flow. Anyone know that this means, I just know its not good.

Identify the substance and don't drive until you know what it is. If it's oil or tranny fluid, neither would be good at all.

 

[mtbtim]

The radiator caps on our rigs do disintegrate. I've seen it on 3 different rigs now. A plastic cap and spring will come off and end up in the top of the radiator. The only way you're going to get it out is pull the radiator and shake it around a bit upside down hoping you can work the pieces out the hole.

Here's a science lesson as it relates to Auto Mechanics from Timmy the Toolman:

Your cooling system depends on the pressure the cap is holding in order to work properly. Think about how a pressure cooker works. The pressure cooker increases the atmospheric pressure inside the cooker and that has a direct effect on the temperature water will boil at. Higher atmospheric pressure means a higher boiling temperature.

When you lower atmospheric pressure, the reverse is true, and water will boil at lower temperatures. Remember the times you visited a higher elevation location and you cooked pasta or something else in boiling water. It took longer to cook, right? That's because atmospheric pressure drops .5 psi per 1000 ft above sea level. Atmospheric pressure at sea level is 14.7 psi and water boils at 212 degrees F as sea level. At 1000 ft, atmospheric pressure would be 14.2 psi. In Lake Tahoe, California which sits at around 6000 ft above sea level, atmospheric pressure would be 11.2 psi and the boiling temperature of water would be much less than 212 degrees F.

Lowering atmospheric pressure to the extreme is what you are doing when you vacuum down an AC system getting it ready to be recharged with refrigerant. When you vacuum down a system, you're removing the air and getting rid of any moisture in the system. Some think the vacuum pump is actually sucking the moisture out but this is not accurate. What you're doing is lowering the atmospheric pressure so low, that water will boil off at ambient temperatures. So, you're not sucking the moisture out but actually causing the moisture to boil off inside your AC system. Check out this link:
http://www.jbind.com/pdf/Cross-Reference-of-Boiling-Temps.pdf
If you look at the chart, if you were able to pull around 29 inches of mercury on your system, and it was 80 degrees where you're at, water would boil off inside your system thus ridding your system of any moisture.

Science lesson as it relates to auto mechanics complete.

 

[19963.4lsr5]

The boiling point of DexCool is close to 270 without a pressure cap. The procedure for my Saturn is to run system with cap off for three fan cycles then install cap. If antifreeze boiled at 212 that would be a big fail


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[tsheaby]

Thermostat

Found this post after doing some research... my 97' 4Runner has been acting up recently when A. Going up into the mountains (increased elevation) and B. When the A/C has been blasting. - I live in Colorado, so its common for me to drive somewhere with an altitude change. Seeing notes on this is very interesting!

Same symptoms! I would park and notice that my coolant overflow tank was leaking coolant and bubbling. Pop the hood and it would be boiling over... eventually the engine started overheating even!

I just replaced the thermostat and so far so good. I tested the old thermostat with the boiling water test, by first placing it in 32 degree F water and then in 180 degree water, which is the temp at which it is supposed to close up. It didn't budge even a little bit so I'm hoping that resolved the issue.

I also replaced the radiator cap with a lever lock pressure cap. Thanks for the insight!!

 

[JayRolla]

Found this post after doing some research... my 97' 4Runner has been acting up recently when A. Going up into the mountains (increased elevation) and B. When the A/C has been blasting. - I live in Colorado, so its common for me to drive somewhere with an altitude change. Seeing notes on this is very interesting!

Same symptoms! I would park and notice that my coolant overflow tank was leaking coolant and bubbling. Pop the hood and it would be boiling over... eventually the engine started overheating even!

I just replaced the thermostat and so far so good. I tested the old thermostat with the boiling water test, by first placing it in 32 degree F water and then in 180 degree water, which is the temp at which it is supposed to close up. It didn't budge even a little bit so I'm hoping that resolved the issue.

I also replaced the radiator cap with a lever lock pressure cap. Thanks for the insight!!

I would get an OEM cap. Those aftermarket ones are trash.