A few days ago, drove to the store and on return a bit later noticed coolant under car on (LHD) driver's side front. Figured oh great the ubiquitous tank split/failure. Looked freaking everywhere and nothing. Knew it was more than strange. I seldom drive anywhere anymore (3,000 miles last year total) so couple of days later went out started car, let it run 15 minutes and = nothing. Okay then this is puzzling.

Yesterday drove to a couple of locations (bank, take out, etc) where I didn't need to shut car off. Got home, couple of trips into house and DAMN! it's pudding again. Popped the hood, and just as I raised it, sun over my shoulder caught what I thought was a single strand of a spider web going from the front of the expansion tank to the battery box. I crooked a finger to sweep it aside to start inspecting for the leak. And lo and behold it was not spider web, but the thinnest single stream of coolant you can envision coming from the middle front of the coolant tank and hitting the rear of the battery box! Well, that's an odd one.

So I surmise the hit/miss of locating the failure was system needed to have some stress on it, calling for maximum cool (it's been a record breaking run of 100°+ F days here this month). and really fully pressurized to leak because it was so small.

It was located here =




Found and ordered a new one (that has a new cap also). The leak stream, not to beat a dead horse, was so fine I question had the light not hit it just right, if I would have seen/found it. And it was leaking only under high pressure, not just really well warmed up car (odd that also).

 

Had similar a few months ago.My leak was from a tiny pin hole where the tiny overflow hose pushes on..Luckily mine was stopped (so far) by moving the hose a fraction tighter onto the outlet. pipe.which sealed the hole under the metal clip and hose.
Hope you sort it.

 

If the expansion tank is starting to leak, best to replace as soon as possible. It’s starting to get brittle and will start cracking. Mine started as a slight leak and the hose connector. When is tried to push the hose on a little bit further, it broke off clean. I was able to make a temp fix with J-B Weld.
Got a replacement tank overnight from Amazon prime. Took about 15 minutes to replace to refill the tank. Just make sure you use the correct antifreeze. (Mine was “Orange”)

 

My tank has now broken for the second time. The tank is fine, but the two small pipes are both broken, and water is leaking from there, or rather steam.
I could hear the fan was on, but nothing to see really on the gauge!!
The giveaway was that the heater only worked when the revs increased! So watch that, it will give you a warning before the gauge.
I checked the expansion tank, and right, no coolant at all.
I took the expansion tank out, dead easy, and it seems in good nick, except for the two small pipes.so I decided to fix it!
Turned two small studs in brass, M6 thread, and threaded the two holes where the pipes had broken off in the tank. . 2.5mm hole through stud, and used superglue to smear the thread before screwing in place. i will use superglue and filler, to bond the outside of the stud to the casing.
I am confident this will be even better than a new tank, as the thin material in this area is a design fault!
If anyone is intrested, I will post a photo!
Happy new Year to all!