Boiling coolant

jimjeep0 · **Posted:** Fri Nov 13, 2009 1:05 am

Had motor replaced with used and am working out bugs. You guys have been a huge help. Has had coolant leak that looks like it comming from thermostat housing, sometimes seems like alot other times nothing.(mechanic who did work says he will fix). Noticed yesterday and today that the coolant is "boiling" in expansion tank. Temp gage is reading normal and dosent fluctuate. Also noticed I have a small crack in the top drivers side of radiator. Should i be worried about motor? would a bad thermostat cause?
thanks goodnight

valvestem · **Joined:** Thu Jul 07, 2005 7:01 pm **Posts:** 222

The coolant is not boiling, just looks that way from... air in the system. I say "air" for the lack of a better term. It may be the system purging any trapped air pockets in the cooling system, it may be sucking air in through the crack you saw-although unlikely, and worse case, a head gasket issue where exhaust gases are going into the cooling system and "boiling" out in the overflow tank.

A quick and easy pressure test of the system will help diagnose the problem, if any.

dgeist · **Posted:** Fri Nov 13, 2009 3:48 pm

Also don't forget that it's a Schroedinger's Cat situation. The coolant behaves differently under pressure (normal) than it does if you open the cap, and you can't see what it's doing unless you open the cap... Is the cat still alive in there?

A good high-temp meat thermometer will confirm the coolant temp for you, and normal is probably in the low 200s anyway.

Oh, and as for the radiator, drain down past that crack and jb-weld the leak. The epoxy should hold quite well as long as you get the area clean first and perhaps scuff it up with some high-grit abrasive. Leaks in coolant system == bad news if left unfixed. I'd fix that before chasing down any other rabbit holes.

Dan

jimjeep0 · **Posted:** Sat Nov 14, 2009 1:42 pm

Dan,
Never even heard of Schroedinger's cat (I know of Pavlov's dogs). I will have to do some research on that. I haven't taken cap off when this happens as it seems that it would spew out very hot coolant. It didn't do it at all yesterday. Well see what happens today.
I want to make sure somethings not wrong with motor like Valvestem mentioned a head gasket or something along those lines, before motor warrenty is gone.

mochodurazo · **Posted:** Sat Nov 14, 2009 1:55 pm

same is happening with a dodge neon 01. i hear boiling water after turning off the engine, and last for 5 minutes to disapear the boiling sound. i just change the recovery deposit. and the sound continues, just ofr input of the subject

Jeepjeepster · **Posted:** Sat Nov 14, 2009 2:32 pm

Need to figure out what the actual temperature of the engine is. That gauge on the dash wont tell you a thing.

If you have a leak the system may not have the pressure it should so its boiling. The coolant can easily get over 212F when idling. Mine goes up to 220F when it idles for long periods of time before the fan kicks on.

Does coolant raise or lower the boiling point?

mochodurazo · **Posted:** Sat Nov 14, 2009 2:37 pm

i'll check with a real thermometer

Boiling coolant

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