So now a test....can you apply your knowledge to a car that isn't a BX?
The car is my newly purchased Rover 216i. The problem....cooling system! Now before anyone just says "head gasket", please read on.
On several occasions now, I've come back to my car having parked it up after a run to find a big puddle of coolant on the O/S/F of the car. At first I assumed it was a flange or a leaky water pump, as its roughly under the timing belt area, but not quite.
However its not a constant leak. It only ever seems to do it once the car has been for a run, and then left to cool. But not everytime either, as I parked it up at work this morning, came back 6hrs later and it was bone dry underneath.
Having just jacked it up and run it hot, I can find no leak at all!
Its bone dry under the car, no real traces of a leak anywhere under the bonnet! With the engine on or off, there was no leaking anywhere.
The only odd thing that did happen, is that I left the cap off the expansion tank while it was running, as I tried the bleed screws to check for any air in the system.....couldn't find any. On this car, there is a small pipe which comes off the top hose and returns to the top of the expansion tank via the head. When you rev the engine, this returns water to the tank, the more being returned varying on the speed of the engine.
While the engine was getting hotter, the level in the coolant tank was slowly rising. I'm told this is normal in these cars, as this return pipe can fill them quicker than they drain. However when the cooling fan cut it, it all pissed out the top like an erupting volcano! In the BX, the level rises and then suddenly drops the second the fan cuts in, so you can imagine I was surprised!
It behaves as good as gold in any other way. With the lid off, and the engine revving there is no bubbling or anything in the tank. The coolant is clean as a whistle, no white gunk in the oil either. It doesn't seem to overheat, and the needle never exceeds the normal position for one of these cars.
My theory was that I'm getting a puddle, because the car is parked up hot, then slowly cools down. The water escapes from the tank as it does, just like when the fan cuts in. I know the cap doesn't hold the water back either, so I was wondering if the coolant is dribbling out, running down the bulkhead somewhere and exiting on the OSF, as the coolant bottle is on the NSF! But again, this theory doesn't hold water (no pun intended) as the car was parked leaning to the left on my gf's driveway.
But why would it burst out like this when the car is being cooled down? I can't work out if I'm leading myself up the wrong path or not here.
So basically..........eh?!
We need the car to go anyway to Devon for our anniversary on the weekend.
Any help greatly appreciated. If you solve the mystery, my 16v is yours for a 30minute countryside blat 
