VS bubbling out of overflow

[Z2TT]

Hi,

My VS has never done anything like this before, ussually it would overheat and the beeping warning would come on (So temp sensor was working, or is that indication of no water), that was when I first got it, I always stopped as soon as it was about to go to the top to protect the motor and filled up the coolant then drove off again. The radiator was leaky so I replaced it with a brand new radiator, flushed the system and refilled with new coolant properly according to the procedures in the books.

Don't think I had a blown head gasket, no smoke at all from exhaust, coolant didn't look murky (even before change), oil didn't have any signs of BHG, no bubbles in rad etc when running etc.

Few weeks driving and driving it would never overheat, never loose coolant and work great. Today though I brang it back, let it idle a bit as i was checking exhaust for leaks, thermo fan would come on here and then, then when I turned it off. It began bubbling out of the overflow, and spilled lots of coolant out, while it was spilling coolant out i popped the overflow open, was bubbling inside, and could feel the overflow hose near the rad cap pulsing.

The car also has a new thermostat and radiator cap that I put in.

Just wondering what could be the problem?

Thanks.

[patmac64]

Hi,sounds like youve covered just about anything i can think of but it does sound like a coolant blockage somewhere!Even though you have replaced the thermostat it may be faulty.If you remove the thermostat and put it in a saucepan with water and heat the water(ON THE WAY TO BOILING) the thermostat should open up if its isnt faulty.Other than that possible head gasket.Why dont you get your cooling system pressure tested?

[hako]

I'd say the problem with overheating that you experienced today is called "heat soak" and it happens when you turn a hot motor off - see this link for an explanation: http://cjbfire.com/Heatsoak.pdf
Maybe also change your radiator cap and check it is the correct 1.35Kpa one.
But if it doesn't overheat during normal day to day driving I wouldn't worry too much...just keep an eye on it.

[Z2TT]

Yep I made sure to get the correct cap, for some reason VS Series II have a 1.35 cap and somewhat thinner radiator core?

Took it for a drive today, about 25 degrees, hardly ever had to turn the thermo fan on during driving as it never got hot, even when coating slowly in traffic a bit,
Got home let it idle, turned it off and all is fine. Will have to do some investigation, wonder if it will do it on hotter days.

None of my other cars have done this even on 43 degree heat, was kind of weird to see it just boil out all the water.

[hako]

They will boil if the cap is not sealing properly as then the radiator is under a lower pressure and will boil at a lower temp. the 1.35 cap raises the boiling point from 100deg to about 130deg so it it's not 100% the car may boil with heat soak. I'd closely check the seals on the new cap and also where it attaches to the radiator as it's not unknown for even new ones to be faulty. Here is a good explanation on the pressure cap (I'm sure you know how it works but just in case!) HowStuffWorks "How Car Cooling Systems Work"

[The1]

So you bled the air out of the system correctly as well?