It was tested on a car that was blowing bubbles in the expansion tank (initial stage of a burnt gasket, followed by tightened collars, soap in the oil cap, and finally soap in the oil dipstick when the problem worsens). The liquid turned yellow, meaning exhaust gases were passing through!
HOLTS Wondarweld was tested, which repairs coolant leaks in the engine block, head gasket, radiator, etc.
A retest was done and the liquid remained blue, meaning the problem was fixed and the repair kit works!! The only drawback is that the black funnel needs to be sealed tightly in the opening of the radiator cap (in open cooling systems) to prevent the escape of exhaust gases, either by cutting it slightly from the bottom or by placing a small bag externally, and with caution because the thermostat must be open for accurate measurement and with a little gas! There is a risk of burns.
At some point, the coolant will rise and then the color of the liquid on the dipstick should not be taken into account, but before this happens.