coolant drops sporadically within 3-4 days

Hi my c3 06 1.4 coolant drops sporadically within 3-4 days. I topped up my coolant to the max level and in about 4 days it goes fully empty. I have checked underneath the car and on the drive too there are no visible leaks and near the coolant reservoir. I have replaced the radiator cap, thermostat and housing but still to no avail. The head gasket was replaced last year so I can rule that out. Could this be the radiator or water pump?

Jjb0800 wrote: ↑Wed Apr 13, 2022 4:03 pm Hi my c3 06 1.4 coolant drops sporadically within 3-4 days. I topped up my coolant to the max level and in about 4 days it goes fully empty. I have checked underneath the car and on the drive too there are no visible leaks and near the coolant reservoir. I have replaced the radiator cap, thermostat and housing but still to no avail. The head gasket was replaced last year so I can rule that out. Could this be the radiator or water pump?

Hi

You can't rule out a head gasket failure when the coolant drops sporadically within 3-4 days and you have done the other checks for leaks.

You should do a head gasket test (here) to be sure and save a lot of time changing bits that have not failed or waste time.

A radiator can leak and you can see this when the engine is hot and the bonnet open.
The water pump can leak, you need to take the cam belt cover off to see.

Should I do a coolant pressure test first and then do the headgasket test?

Jjb0800 wrote: ↑Wed Apr 13, 2022 4:31 pm Should I do a coolant pressure test first and then do the headgasket test?

It doesn't matter what order you do the tests in, but it is important to do tests to save changing parts that are not faulty.

Jjb0800 wrote: ↑Wed Apr 13, 2022 4:03 pm I topped up my coolant to the max level and in about 4 days it goes fully empty. I have checked underneath the car and on the drive too there are no visible leaks and near the coolant reservoir.

If you are loosing coolant into the engine at that rate, the engine should run rough at idle.

Jjb0800 wrote: ↑Wed Apr 13, 2022 4:03 pm The head gasket was replaced last year so I can rule that out.

You can get damage (corrosion) between the water galleries and the combustion chamber on the lower face of the cylinder head.
The TU3 engine has "wet liners". The head gasket forms a very thin seal around the top lip of the liners and it would be easy for the gasket to fail there if the surface is not prepared correctly.

As Arfur says, you need to be sure that it's not the head gasket, if you cant find any other signs of coolant leakage.