My car is a UK Diesel Honda Accord 2.2 CDTi
So I've had a problem with my car for about a week, it started overheating and not accelerating when I put my foot down on the accelerator (losing power)
I realised after the first time it happened that it's because the coolant level was below the minimum in the reserve tank
So I topped it up with about 0.75 litres of tap water and the engine temperature was ok after that, drove it a couple hundred miles over the next few days and then had to top up the reserve tank again because it was low, but the car did not have any problems with overheating or losing power
A mechanic friend brought over a pressure testing kit which he used to increase the pressure on the coolant system to 1.5 bar (the system is rated to 1.3 bar) and we ran the engine for about 20 minutes but couldn't see any water leaking from anywhere in the engine compartment, water pump, any of the hoses, radiator or exhaust
There's no white gunk in the oil filler cap, or in the dipstick so I don't think it's a gasket
I can't see and haven't seen at any time water dripping from anywhere underneath the car or in the driver or passenger foot well
Any ideas where the water could be going? It must be about 3-4 litres now over a week, the coolant system holds 6.3 litres according to owners manual
EDIT: I've ordered a UV dye and trace kit to see if that helps trace the problem, will update once I've had a chance to use it
UPDATE 28-07-2019: Have tried the UV dye for a few weeks now but still haven't been able to find the source of the leak, tried another liquid called FIXT engine coolant stop leak but I think it's still losing coolant, perhaps more slowly than before. The car itself runs fine otherwise