Jonny K

After driving my car hard (which is usually how I do it) and inspecting the coolant reservoir I find it boiling. The coolant level seems to keep decreasing because it'll boil over when hot. Then when cool, I'll get low coolant warnings (when taking hard corners). Do I have a coolant issue?

4Driver4

You might have a problem with the fans, t-stat, or coolant cap.

Jonny K

The thermostat was replaced about a year ago, the coolant cap came with my new reservoir so I assume it's a good seal, and my coolant temperature is always the standard 90 C.

speedtek

Only reason it will boil is if the system is depressurizing, most likely a leaky resevoir cap or a cracked resevoir.

4x5x5

Either your gauge/sensor is wrong, or your system is backing up much hotter fluid somewhere. Water doesn't boil @ 90C and coolant and water sure don't boil @ 90C, and most definately not if your system is holding pressure would it evn boil @ 100C+.

Sloooo4esT

i looked at my coolant resevoir and found the coolant almost not there, just lots of bubbles, turned out the water pump was spinning so fast coolant was not getting through, maybe if you were driving hard enough this could be what happened?

4x5x5

I'd sure check on that. The coolant system is closed, i.e., no where for coolant to go. If your level was off the charts low, then you have a leak. If your WP is not pushing coolant, your in a world of hure especially at the track. Hard driving will not change the level of a full system.

MacWorld

Is your coolant boiling with the reservoir cap installed? It is normal if it starts boiling when you open the cap, the pressures drop and the boiling point of the coolant gets lower.

PV=nRT (http://en.wikipedia.org/wiki/Ideal_gas_law)

Pressure * Volume = number of moles * Universal Gas Constant * Temperature

If you lower the pressure then something else must change: the volume, the temperature or both.

Yes this is a law for the gasses, our boiling coolant is on the point to get to a gas so we can understand what's going on with this law.

I had this happening with my '89 Jetta even at operating temperature, only the action of opening the cap got the coolant to boil. This is why they recommend never opening the cap when the engine is hot, overheating or not.

BTW my explanations are probably not the most accurate of them all but it is only to explain a bit the idea.

UrSobsessed

bottom line, NO. In hotter weather, I would hear gurgling coming up into the x-tank from the t-stat. I'm not sure if this was good or not. I didn't get anything definitive here when I asked. I have gone through my entire cooling system, except the rad and head gasket since then. I'm hoping it has stopped. I haven't heard it since then anyway.

Things to consider:

Blocked radiator-maybe flush it?
Head gasket leaking letting air in the system from the cylinders.
Faulty x-tank cap-even though it's new, it could have been a defective one in the first place.
If you haven't yet done it, replace the MFTS. It's easy, and it will give you an accurate reading of your coolant temp(these can go bad and mislead you). Also, replace your fan switch (in the bottom right of the rad) to make sure your electric fan will operate when it's supposed to.
Viscous coupling-if your motor is hot, you should hear your fan(not electric) moving air, especially if the window is down.

Sorry to load you with stuff to think about here. I'd start with the easy stuff, and go from there.

HTH

UrSoccer_mobileĀ®

Is the fan sensor the one on the bottom left of the radiator?