Low Coolant - Single Episode Only

[AUSTSE]

My 18 month old Aurion's coolant has always been at about the half way level on the reservoir container, until a week ago when I found it to be almost empty (obviously not low enough to show a warning lamp on the instrument panel). My thorough search around the engine and radiator with a torch failed to locate any obvious leaks. I topped it up and have since driven 1,700km incident free (in hot weather) with no further evidence of coolant loss; during this time the car has operated perfectly with the engine Temp' gauge sitting at the normal point, just below the symbol. Any idea as to why the regularly checked coolant was low on only one occasion?

[DJKOR]

Was it sudden, or how long was it since you last checked your coolant level? What has the temperature been like over all the time you have been keeping an eye on it?

With my Aurion, I've had the same deal but this was caused by hot coolant managing to boil/evaporate past the lid on the reservoir. Since the reservoir is there to handle the overflow of coolant as it heats up and expands there is the possibility that in really hot conditions, the reservoir can fill to a high level and coolant from there can work it's way past the seal over time from evaporation or even more worse case, overflow. Then as some coolant gets lost and the engine cools, it sucks the coolant out of the reservoir and it can get to the point that the level reaches low.

On a side note, having an empty reservoir will not necessary cause overheating. As well, if a radiator coolant level sensor was present (which the Aurion doesn't have), having little to no coolant in the reservoir would not cause any warning lights as it is just the reservoir.

[AUSTSE]

Was it sudden, or how long was it since you last checked your coolant level? What has the temperature been like over all the time you have been keeping an eye on it?

With my Aurion, I've had the same deal but this was caused by hot coolant managing to boil/evaporate past the lid on the reservoir. Since the reservoir is there to handle the overflow of coolant as it heats up and expands there is the possibility that in really hot conditions, the reservoir can fill to a high level and coolant from there can work it's way past the seal over time from evaporation or even more worse case, overflow. Then as some coolant gets lost and the engine cools, it sucks the coolant out of the reservoir and it can get to the point that the level reaches low.

On a side note, having an empty reservoir will not necessary cause overheating. As well, if a radiator coolant level sensor was present (which the Aurion doesn't have), having little to no coolant in the reservoir would not cause any warning lights as it is just the reservoir.

Thanks DJ'

I checked the level every two to three days.

Your reply seems logical and the level has remained constant since my original coolant post.

TA