coolant bubbling after shut down...
 

ok am I right that if I hear the coolant bubbling after I turn off the car that I just need to add more coolant to the system? I heard it bubbling today, I didn't see any crazy temps or anything but I am just wondering if I have to right idea on what I am supose to do, is there anything else I should be doing instead of just adding coolant? Thanks

No, you shouldn't be adding more coolant.

We just discussed this a couple of weeks ago. RonK thinks it's air in the system or coolant seals - I say it's the 30 lb cast iron heat sink (exhaust manifold) on the exhaust side causing boiling.

Search......

i agree with the boiling. all cars will send some coolant to the overflow tank when hot ours happen to stay really hot

It's likely air as the coolant runs back into the overflow and AST still under pressure. After swapping out with a Pettit AST, topping off and burping I havent heard a peep out of it, just normal heat soak "ticking". It gurgled like rythmic percolating coffee before tho. You could feel it leaning against the fender, like the car had bad indigestion.
:)

This is exactly the same as my car... before the new AST it was bubbling, after installing the AST the sound was gone!

Think of the engine as a coolant pump to and from the overflow bottle. When the engine warms up the coolant expands and forces its' way through the overflow tube into the overflow bottle. When the engine cools down it creates a vacuum, which sucks coolant back from the overflow bottle.

This works fine until one of your coolant caps develops a vacuum leak at the rubber seal. Then all that happens is some percentage of the coolant in the engine is pumped into the overflow bottle and remains there, leaving the engine a little low. This allows the pressure to drop after shutdown (because air is compressible), which in turn allows the coolant to boil after shutdown. The metal in the engine holds a lot of heat when the engine is running, and this is ok as long as there is coolant flow to carry it away. Once the flow stops, the coolant will heat up more than normal, and if the pressure is low enough, it will boil.

The classic event run is you notice the engine coolant level is way down (checking when cold, of course) when you look in the water pump fill tube. You pour in more water. It gets pumped into the overflow bottle (to stay as you have a vacuum leak and can't get it back to the
engine). You are now nervous, and check the level in the engine every day (morning when the car is cold), and fill it. Soon (two to three days) the overflow bottle is full to the top and leaks out where the filler tube (removeable) joins the bottle. You see the puddle and panic.

It happened to me. Solution - replace both caps (they were old), replace all small coolant hoses to/from overflow bottle (they are not designed for pressure use as there is no pressure in this part of the system, so they are thin and can be collapsed under suction - stopping the coolant from returning to the engine. I replaced them with suitable pressure coolant hose routed so it would not kink (it's thicker so care must be taken when routing it - it will not bend as well).

Hope this solves your problem.

well what are the ill effects of the bubbling (boiling) is it that the bubbles put space between the coolant and the metal so the metal loses it's ability to cool as well and heats up to an extreme? Is it anything else as well or am I completely wrong in the first place

clayne - here is where I got the idea that I was supose to add more coolant https://www.rx7club.com/showthread.p...olant+bubbling (The second post/first response)I did search but I thought it sounded weird so I started a new thread and asked my own question, I don't mean any disrespect I know you are more knowledgeable than me I am just showing that I did search, I appreciate all of the help guys.

The boiling really has no effect I can think of other than causing anxiety in the owner ;) . I was going to say it's bad for the coolant, but the temp. would be about the same. It's only boiling because the air pocket compresses enough to let it (effectively lowering the pressure). The fact that the coolant in the engine is a little low could allow bubbles into the coolant "stream" that cools the rotor housings. This could cause local hot spots. It -could- even be blamed for "O" ring failure (perhaps a bubble allows a spot to heat up greatly then cool, then heat, etc. weakening the aluminum). I haven't heard anyone raise this possibility though so perhaps I just have a good imagination ;) .

Bottom line is you probably need to do a little work on the system (new caps and/or small hoses). I think that is the major effect - it's a warning something needs attention. I do know some owners consider the boiling "normal". I do not because I found it easy to fix.