Boiling sound when shutting the truck off?

[over2land]

Despite my somewhat elevated idle, I'm driving the truck.

And, when I shut it off, and pop the hood, I can hear what sounds to be boiling water from under the hood.

I'm not losing coolant, nor am I over heating.

Is this a normal condition of the lovely closed cooling system?

BTW, it's an 88 MJ with a 4.0

Thanks.

 

[XJack]

May be boiling coolant mix.

Or it might be oil running back down into the pan.

 

[over2land]

the stupid plastic overflow tank doesn't show any bubbles in it.

When my Camaro was over heating, it'd have bubbles coming up into the overflow tank.

If it doesn't overheat, should I worry about iT?

 

[jdougn]

My '98XJ did this when I first got it. I finally figured out it was contaminated oil in the front differential. After it was driven for awhile the oil & water in the diff would get hot and boil. It finally boiled out the vent tube & that's when I figured out what I was hearing all the time. Luckily it wasn't driven much before it was corrected. hth

 

[over2land]

Interesting, but since mine is 2WD, dunno if that applies....

thanks though

 

[90xjpos]

its in the coolant lines. probably betweent he radiator and thermostat. nothing to be alarmed about yet just air pockets. and after getting to temp they can run back through the thermostat. thats what your hearing. you might want to let them out though. sometimes a bunch of lil air pockets gather in one place and create a vacume situation. which will cause a sudden overheat. which wont read on the guage. it'll just kill on you. it's simple to bleed out. just simply pressure test the radiator. a few times. you will see the bubble start to show in the overflow after your first few tries

 

[Dr. Dyno]

I can hear what sounds to be boiling water from under the hood.

If you're hearing what sounds like boiling water, there's a good chance that it IS boiling water. The most likely place for that is the coolant expansion bottle. If the bottle isn't cracked and the pressure cap is good, the system should be pressurized enough to keep the boiling point of the coolant high enough to prevent it boiling off. Therefore check the cap and check the bottle for cracks; a fine hairline crack is enough and it may be hard to see.

 

[Purple]

im getting the same thing... but mine does that around gas tank cap area, its a 98. checked the breather hose and also did about 4 diff oil changes over the past year, and it still does it. I figured it must be the pressure relief lines that come from the tank or something..