one of the problems, skellum, is even if you see the dripping of coolant under the car and on the passenger side.. that doesnt mean its where the leak is..
as ajsmith66 suggested " As a basic test you could use an old pressure cap, drill it out and fit a tyre type valve and then use a foot pump to pressurize your system, worked a couple of times for me but not always, but for about £1 its worth trying, just don't connect to an airline as you'll blow a hose."
i made a similar thing to pressurize the system, but in a bit of pipe that connects in series with the jiggle pipe return into the header tank.. with a 2 bar pressure gauge in it ( the system under pressure will vent through the pressure cap over 1 bar ) so i could check not only for leaks but the operation of the pressure cap..
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it cost me £11 then.. i see its gone up... to £18 now.. such is life..
here is the thread i started when i was investigating... and pick of the pipe in situ, before i fitted the omega pressure gauge...
of interest, i did try driving the car with the pipe and gauge in place, to see if i could get it up to pressure and read that on the gauge when i stopped.. but even though i could get the car hot... i couldnt get the gauge to climb toward one bar at all...
i haven't pursued that ... but it should have told me i had a leak i couldnt see somewhere... which i did... HGF eventually, even though the car ran nearly a year on from that time.. without fault on emissions.. passing its mot...
the next mot after that it failed on emissions.. and i knew i had a leak i couldn't locate.. it was the head gasket..
thats now been replaced and dont loose coolant at all..
i think i should refit the gauge pipe, and see if that makes the pressure climb visible on the gauge..
of particular note. the vent caps are not reliably leak proof.. a fully working vent cap is designed in such a way it cant allow vacuum in the system. only the one i made by removing the vent in the cap and sealing it.. stopped leaks. a normal vent cap leaks.