Aussie_Dark
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Hopefully someone will be able to guide me to work out what has failed.
I have already had the radiator cleaned, had the cooling system pressure tested, and I have replaced the cap twice as I know the caps are unreliable. Also the fans seem to cut in appropriately. There are no leaks apparent. The exhaust does not appear to blow steam, and there does not appear to be any coolant in the oil, or vice versa. There is no strange residue around the oil filler cap.
What normally happens is that the car temperature gauge stays around the 25% mark for approximately half an hour of driving and then will shoot up rapidly to 100% and the overheat alarm sounds. It doesn't need to be a hot day for this to happen.
On a cool to cold morning the temperature stays just below the 25% mark. On these occasions there is no drop in coolant and the overflow reservoir stays at the same level.
On days where it hasn't overheated, but the temperature has drifted a little above the 25% mark, I have found that more coolant has been pushed out into the overflow reservoir than what is sucked back, but it isn't a huge amount. All checks of the overflow reservoir have been done after the car had completely cooled down.
On a couple of occasions I have had the temperature operate at the 25% mark, shoot up wildly to around 75%+, shoot back down to normal, shoot back up again, then down and stay down until I got home. On another occasion it continued to shoot up and down for the whole journey (but on all of these occasions it was about 30 minutes before the strange behaviour started).
I have removed the radiator cap and watched the water circulating as the car gradually heated up. The first thing I observed is that bubbles appeared every so often as the water circulated. If I slightly pressed the accelerator the water will overflow. Every so often the bubbles became extreme to the point of the water foaming, and then return to bubbling every so often. The water level also fluctuated up and down. After approximately 30 minutes (and rapidly without any real warning) the water appeared to boil with steam and water spurting out. A check of the temperature gauge indicated that it was still only a little above the 25% mark.
So what I have concluded is that with this problem, the gauge may be still be at around the 25% mark with the system being hot enough to push coolant out of the overflow. I'm assuming once enough coolant is pushed out that the temperature will start fluctuating or rapidly hitting the 100% mark.
Any pointers to what could be the problem would be greatly appreciated. I am down to the water pump, thermostat, or head gasket. None of these are things that you want to fork out to fix without some hope of being right.
I have already had the radiator cleaned, had the cooling system pressure tested, and I have replaced the cap twice as I know the caps are unreliable. Also the fans seem to cut in appropriately. There are no leaks apparent. The exhaust does not appear to blow steam, and there does not appear to be any coolant in the oil, or vice versa. There is no strange residue around the oil filler cap.
What normally happens is that the car temperature gauge stays around the 25% mark for approximately half an hour of driving and then will shoot up rapidly to 100% and the overheat alarm sounds. It doesn't need to be a hot day for this to happen.
On a cool to cold morning the temperature stays just below the 25% mark. On these occasions there is no drop in coolant and the overflow reservoir stays at the same level.
On days where it hasn't overheated, but the temperature has drifted a little above the 25% mark, I have found that more coolant has been pushed out into the overflow reservoir than what is sucked back, but it isn't a huge amount. All checks of the overflow reservoir have been done after the car had completely cooled down.
On a couple of occasions I have had the temperature operate at the 25% mark, shoot up wildly to around 75%+, shoot back down to normal, shoot back up again, then down and stay down until I got home. On another occasion it continued to shoot up and down for the whole journey (but on all of these occasions it was about 30 minutes before the strange behaviour started).
I have removed the radiator cap and watched the water circulating as the car gradually heated up. The first thing I observed is that bubbles appeared every so often as the water circulated. If I slightly pressed the accelerator the water will overflow. Every so often the bubbles became extreme to the point of the water foaming, and then return to bubbling every so often. The water level also fluctuated up and down. After approximately 30 minutes (and rapidly without any real warning) the water appeared to boil with steam and water spurting out. A check of the temperature gauge indicated that it was still only a little above the 25% mark.
So what I have concluded is that with this problem, the gauge may be still be at around the 25% mark with the system being hot enough to push coolant out of the overflow. I'm assuming once enough coolant is pushed out that the temperature will start fluctuating or rapidly hitting the 100% mark.
Any pointers to what could be the problem would be greatly appreciated. I am down to the water pump, thermostat, or head gasket. None of these are things that you want to fork out to fix without some hope of being right.