Hyundai Repair: Cooling system problems, radiator cap, expansion tank

Question
Hi,

I live in China and own a locally made Hyundai Refine 2.5L van (sold in other countries as H-1 or Starex) that has a cooling problem. Despite it's not made in the USA, I think my question is very generic. I just wanna know before I take it to the garage and I can't find anyone else to ask this question.

Basically when I turn off the engine the level of the coolant liquid in the expansion tank will rise rapidly and often overflow. Surprisingly, at the same time I see plenty of bubbles coming from the radiator back to the expansion tank. Looks like boiling...

The temperature reading is always OK (never above 90 C).
Sometimes I get a luminous warning (the icon of an engine in orange). What does this mean?

The thermostatic valve was replaced but nothing changed.

Looks like there was plenty of air in the cooling circuit. Absurd? Any chances the circuit is taking air through a bad fitting (i.e. a crack right before the cooling pump, so it is sucking air in)?

Could it be a problem in the pump itself?

The two little fans facing the radiator do turn on and off often, but never stay on afer I turn off the engine. A friend told me this could be why. Is that so?

Thanks in advance and bes regards.
Tony.

Answer
My first suspicion is that you may have a problem with your radiator cap sealing properly.  This can allow air into the system and also allow the rapid increase of coolant in the reservoir.  The fact that your coolant gauge remains normal suggests that you do not have a significant cooling system issue (i.e., your engine doesn't seem to be overheating).  Check your radiator cap and radiator filler neck.  I'm presuming the reservoir isn't overfilled.  If it is, you'll need to reduce the coolant to the proper level to prevent expansion of the coolant to the point of coming out of the reservoir.

If your radiator cap is working properly, the system should not be able to suck in air.  A properly operating radiator cap will prevent the buildup of a vacuum in the cooling system.  Similarly, there's no reason to suspect the problem is with the coolant pump.

It's normal for the cooling fans to cycle when the engine is on.  This means they're controlling coolant temperature effectively.  On most vehicles, the fan circuit is designed so the fans will not operate when the ignition is off.  While the coolant will expand from additional engine heat after the engine is turned off, the level in the reservoir should not rise grossly and quickly because of this.

It's unlikely but possible that the orange lamp (sounds like a "check engine" lamp) is related to your coolant issue.  You'll need to have the diagnostic trouble codes read to determine the nature of the problem causing the lamp to illuminate.