Recall on Coolant caps

[Joji]

All right I am making some progress. I finally have the coolant level right below the max line when the car is cool. The Temperature light above 250 is off now. The new cap I ordered from Sunset works with no hissing and leaks. The only thing I notice now is when I open the trunk after a drive it sounds like the coolant is boiling. Far as I know coolant can't boil. Is it the water mixture boiling? do you think it is boiling at all.

Also if it is wouldn't the coolant tank melt since it is plastic

I also smell a slight burning smell now. not sure if it is related

thanks

[Jaxonalden]

Joji,

Quote;
Q-"Far as I know coolant can't boil." A-Yes it can, adding anti-freeze raises the boil point of water (212 degrees). The radiator cap is set at a certain pressure (8-15 psi) this pressurization of the coolant system also raises the boiling point.
Q-"Is it the water mixture boiling? do you think it is boiling at all." A- Not possible, the water and anti-freeze is a mixture. If it was the engine would be so hot that you would be getting an idiot light and the temp gauge would be well above 230 degrees.
Q-"Also if it is wouldn't the coolant tank melt since it is plastic." A-The melting point of the tank is well above the boiling point of the coolant. If the tank ever melted, you would have bigger problems on your hands than the tank.

[roadracer311]

Are your cooling fans coming on? Boiling suggests something is really wrong with your cooling system, like a stuck thermostat or cooling fans that fail to come on.

[Joji]

I checked the 2 in the front. I hear them come on. But the wierd thing is that 6 months ago I heard the left fan in the front sound like it was miss aligned. it was making a bizare noise. I was just about to bring it in but it went away. I did have the thermestat chaned recently when the water pump when out. but maybe it is a bad one or not instaled right. How do I check that?

How do I check the fans if they are spinning the rigth amount. Any type of tool or way of testing it
thanks

[turbo23dog]

I think that if you are hearing a boiling sound then your cooling system is not holding pressure or air tight. Since you've been through a couple of coolant caps, this leads me to believe the cap is not the problem but likely the tank or a hose at fault and the reason the system is not holding pressure.

BTW, the pressure is what keeps the coolant from boiling. Going too far back on my chemistry lessons to explain better but temp and pressure are related...

[Jaxonalden]

FYI;

A 1:1 mixture of ethylene glycol based anti-freeze and water raises the boiling point of coolant to 225 degrees, from 212 of straight water.

A 15 psi coolant system in turn raises that same coolant boiling point to 265 degrees.

Above those temps the coolant can't cool the engine any longer because the boiling (bubbles) actually insulates the coolant from the metal surface (cylinder) and engine temperature then raises (fast!) to the melting point of the pistons.

[turbo23dog]

Originally Posted by Jaxonalden

A 1:1 mixture of ethylene glycol based anti-freeze and water raises the boiling point of coolant to 225 degrees, from 212 of straight water.

A 15 psi coolant system in turn raises that same coolant boiling point to 265 degrees.

In my post above, I meant to say that pressure as well as antifreeze work to raise boiling point.

Aside from the temp/pressure and boiling point discussion, this problem reminds me of an old BMW I formerly owned (84 533i) that used to overheat frequently. After replacing all the obvious cooling system items, which did nothing, it turned out that the cylinder head was cracked and allowing exhaust gasses to enter the cooling system, thereby causing an air break and boil over.

Any chance this Boxster has a cracked cylinder head causing a similar problem?

[RandallNeighbour]

Originally Posted by Jaxonalden

FYI;

A 1:1 mixture of ethylene glycol based anti-freeze and water raises the boiling point of coolant to 225 degrees, from 212 of straight water.

A 15 psi coolant system in turn raises that same coolant boiling point to 265 degrees.

Above those temps the coolant can't cool the engine any longer because the boiling (bubbles) actually insulates the coolant from the metal surface (cylinder) and engine temperature then raises (fast!) to the melting point of the pistons.

Most of you never knew MNBoxster, but if he had read this I am sure he would have countered with all sorts of physics-based opposition just to be contrary!

Jaxon, thanks for this info. I love learning these kinds of things from everyone here on my home away from home, 986forum.com.