Chris old fruit.. that gurgling noise is air in the system.
It's in there because the coolant level has dropped and air gets drawn in through the filler cap to replace it. The cap will only hold 1 bar of postive pressure or vaccum.
The coolant must be going somewhere... If you get under the nose of your motor and peer at the radiator, it should be completely dry at the bottom, as it has not rained for a few days (down here in the sunny "Land That Time Forgot" anyway..)
If you detect moisture on the radiator mounting rail (or inside the bumper), you have a coolant leak. If the hoses are tight and in good condition, then it's more likely to be the radiatore, as it's getting on a bit now.
You can dry everything up and then rattle the old radiatore around a bit.. if it leaks more... that will rather prove it.
If there is REALLY no leak, then you could be looking at what my mechanic fellow calls a "shagged" head gasket. That may be causing the engine to suck coolant in (are you seeing a lot of condensation out of the exhaust pipe?) or blow exhaust gas out... into the coolant.
What happens in the case of the latter is that the gas then pressurises the coolant. This increases the pressure in the system until the coolant sprays gas and coolant out of the radiator cap (1 bar, remember). Do you see signs of spray under the bonnet or over the radiator at the reservoir cap end?
Once you have air in the system, you're on a hiding to nothing old fellow... The rad' has a sensor which constantly monitors the temperature of what's in the radiator. If it's hot, hot coolant it will turn the fan on.
Obviously, with less coolant in the system (and more air) the coolant becomes hotter much more quickly.. and as it's only passing through half the radiator (the other half.. the top .. has air in it) it also does not get cooled as much as it normally would, if it had the range of the entire radiatore to roam around in.
So, the coolant gets hot quickly.. then it is not cooled fully.. then goes back into the engine block... where it becomes hotter still. The temperature sensor switches the fan in very frequently as you have noticed. Feel the radiatore (don't put your hand inside the fan, in case it kicks off.. I presume you are attached to your fingers?) Is the top half of the radiator cold, when the bottom is stinking hot..?
Worse is to come, even though you undoubtedly assumed that your problems could not increase. Once the level of the coolant has fallen below the level of the sensor (it's that brass nut thing with a pair of wires attached in a single connector block) the sensor can't measure the temperature of the coolant any more. If you cast your mind up a few lines, you'll see that the air in the radiatore is cooler than hot coolant.
So, the sensor thinks everything is kosher, even though the radiatore is not Jewish at all. It does not activate the fan (even though the fan would be blowing cold air through an empty radiatore) and so the engine will get hotter and hotter and hotter and finally melt.
It may strike you as imperative therefore, to identify the cause of the coolant loss in your donkey. The best scenario may be that a loose hose or leaking clip may be causing coolant loss under pressure (as the coolant heats up). If so, replace the defective part.
It could be the radiatore.. they are plastic and zinc-plated steel and alumium.. but wear and tear or vibration allied to some corrosion may have rendered it unserviceable.
Finally it may be that you have a failed head gasket. The reparation of this is a less than attractive task.. requiring some dismantling of the engine components. You can test for a gasket failure by performing a Carbon Monoxide test on the coolant. Your local garage will have some chemical analysing liquid that changes colour when mixed with coolant that has been exposed to exhaust gas.
Ralf S.
