Coolant in expansion tank dissapearing

Hello guys.
I have this really strange issue with my car, but it is a looong time between it shows up, and wanted to ask if any of you ever had experienced something simelar.

The coolant fluid in the expansion tank sometimes just dissapears, and the really strange thing is that not 1 drop of water is missing in the engine itself… I had the expansion tank out and checked it well and truly for leaks and there are none, I even changed the headgasket, water pump and all other things with the 60k service, and it still does it from time to time… It can be 3-4 months between and I have even had almost 1 year go by and then all of a sudden the water just dissapeared…

I feel like I am chasing some ghost as this thing is more of a mystery then anything else I have ever dealt with on a car.

If anybody has some ideas/suggestions, then I am happy to put my ear to the listening advice :slightly_smiling_face:

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Have you checked the filler neck nipple the hose and expansion tank cap for blockage ?

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Yeah, I took em off, ran a wire through them and also water just for measures… The thing is that it is that there is no indicator of when the water might have gone from the tank, because it can be months between the indicator light coming on, and sure enough when it does the water in there is low, but all the engine still has water all the way up in the filler cap, and even if I turn the car on and leave the filler cap off, the water level never drops

Dude, your engine might be burning coolant. Check the color of your exhaust smoke. Head gasket could be cracked, or the block could be cracked. When the engine needs coolant it will take from the reservoir. I had a Tercel in the 90’s and those were notorious for rusting. My radiator rusted a hole in it and leaked coolant. reservoir was empty every time I checked. I started filling it with water every 2 miles :joy: until I could change the radiator. I never noticed a leak. Just engine starting to heat up and empty reservoir. for sure, you are leaking somewhere. Coolant doesn’t just disappear. Got to find out or you could get into a bind. Right now your car is not over heating, thats good. Find the problem and fix it or you’ll be filling up the reservoir every 2 miles like I did :joy: and when you over heat, the engine dies.

Check the hoses too. Cracked hoses from dry rotted plastic are notorious for leaks. Check the entire pathway for the coolant. Heater core, thermostat, and as I already mentioned, the radiator. Look under the car for small puddles after you have been parking for a while.

It is really bonkers crazy… When I wrote this post I had 2 times prior just made a small fillup into the expansion tank with around 3 months between each, and it was a small amount that went in there… It was just so the indicator warning light turned off again, and I checked right now just for good measures, and it does not look like 1 single drop has dissapeared…
The headgasket is recently changed aswell as water pump and all those things… Did a 120.000 km service where basically everything that needs changing got changed aswell as hoses and etc. etc. etc.
That dissapearance of coolant came out of the nothing, and it seems like it has vanished out into the vast spaces of nothingness again… Really really strange, but I dont want to worry about it when it seems like it more or less has vanished again :rofl:

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This is truly incredible… 1 year later and the excact same thing happend… The water in the expansion tank had gone so low that it activated the low coolant warning light in the dash… This is such a mystery that I have no words for it…
Put a little in it and all is good… This same excact thing has been happening every year at excactly the same time after winter, and then it will not show up again for several months… Life´s little mysteries :grin: :grin: :grin:

I had this type of issue on my truck once and it was a pinhole that was misting out coolant gradually on one of my radiator lines.

Took forever to figure out because the coolant would dry up so quickly there was no sign of it leaking with such a fine mist.

Check the seal on top of the expansion tank, or maybe just replace it, I have been doing some research on the cooling system lately and it’s very interesting the way it works. Replace the filler cap also, these are also prone to failure.

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Can the seal on the expansion tank be sourced anywhere?? I have not really ever seen it :face_with_monocle:

Honestly I’m not sure if replacement or check and repair is better. I’ve been reading about this and will have to re-read a few times to get my head around it but the bottom line is that the seal on the filler cap and the seal on the expansion can result in coolant loss if not operating properly. The filler cap was one of the first thing I changed when I got the car due to Robs recommendation at the time and he tried to explain to me why but that’s a few years ago now.