On Thursday I swapped out my leaky top hose - the bleed screw was shot, and thermostat (I've made that a habit - they always seem to fail as soon as they're refilled). Couldn't bleed the system 100% as it wouldn't get up to temperature - presumably just too cold out to manage that while stationary. But Friday I went for a drive, up to temp no problem, and topped it back up again after. All seemed well.
Saturday drove a couple of hundred miles, and lost about an inch from the level on the header tank again. A little miffed, looked around for leaks, but nothing seemed to be dripping. Topped up again for the same drive home again, stopped for food just half an hour down the motorway, and came back to a big red puddle under the driver's door. A peek underneath and it was dripping profusely from the chassis; looked like it was actually coming out of one of the holes. Could see a wet, red area on the top of the chassis looking behind the driver's side wheel.
Well we needed to get home, and had about 3l of coolant, so we set a timer to check it again in another half hour. Topped up the inch or so it had dropped, and set off. Half an hour down the road we pulled over again, opened to have a look - completely full, and no sign of anything dripping down from the chassis at all. Even the bit behind the wheel was dried up. Confused we set off again, and reset the timer. Stopped to check, and once again no sign of any leaking whatsoever.
OK, two differences we can think of:
1. The first half hour we started with the heater on for a bit and haven't had it on at all since; maybe it's only that loop that's leaking
2. The engine had a bit of time to cool down at our first stop, and we were checking just moments after stopping the other times.
Well 1. we can test, right; so once we got to half an hour from home we turned the heater on. Warmed up, no leaks in the cabin (that's what we'd get from a worn out heater matrix, right?) and no problems. Arrived home and checked the level - totally fine.
OK, 2. then. Checked it a few times across yesterday evening, and again this morning - nothing. Still completely full.
I'm really confused haha.