24 minutes ago, TomsFocus said:

I think you're missing the point here lol.  

If you buy the pre-mixed berry screenwash, expecting it to protect to -10, just pour it in and it'll do that...

If you spend more on the concentrate, expecting it protect to -10, and then dilute it by 25%, it's then only good for -7.5...dilute it 50% and it's then only good to -5c.  But they still write '-10' on the front.  You'd have to use it neat, costing more than the ready mixed, to get that -10c protection.  

Just checked my garage, I'm using the Halfords -20c 5l concentrate which I bought on offer at £4, being in NI, I should be just fine LOL

I just checked the foot well and no signs or smells of it leaking. So what else could cause it to drop that much without anything obvious showing? The cap was slightly lose when I touched it but it’s quite lose anyway as it’s a new one. It clicks into place when screwed all the way 

Back to the OP's original question on coolant loss:

There could be 2 reasons for the "loss":

1. A leak. If not obvious, have a pressure/vacuum test carried out on the system.

2. Air trapped in the coolant system after the water pump was replaced, has gradually moved to the coolant tank, and the tank contents has replaced that air. A common occurrence on cars, if not bled fully.

Not sure what you mean by "The cap was slightly loose when I touched it but it's quite loose anyway as it's a new one".

15 minutes ago, YOG said:

Back to the OP's original question on coolant loss:

There could be 2 reasons for the "loss":

1. A leak. If not obvious, have a pressure/vacuum test carried out on the system.

2. Air trapped in the coolant system after the water pump was replaced, has gradually moved to the coolant tank, and the tank contents has replaced that air. A common occurrence on cars, if not bled fully.

Not sure what you mean by "The cap was slightly loose when I touched it but it's quite loose anyway as it's a new one".

I bought a new cap and it’s not very stiff when doing it up. It does click into place thought  when tightened. When I touched the cap I noticed it was a little loose but not enough for evaporation to occur I wouldn’t imagine. I’ve driven 50 miles since topping it up yesterday and it doesn’t appear to have dropped

2 minutes ago, Jason87 said:

... When I touched the cap I noticed it was a little loose but not enough for evaporation to occur

Highly unlikely a 'cap' would be the cause of that much coolant loss, I too was told that when my system starting losing fluid until the matrix fault reared it's head...

Have you checked it's not the coolant tank itself that is leaking? I've had to replace this on mine as it had some hairline cracks on it.

Mechanic said it’s the thermostat housing I believe which is common on these?