Coolant concentrate

Q I would appreciate your advice. I have a 2016 Vauxhall Meriva B with the

1.4 turbo petrol engine. In preparation for winter, I checked the antifreeze concentration with a refractometer. It showed protection down to -10°C

(it should be in the region of -30°C). Rather than draining and refilling the system, I propose to empty the expansion vessel and fill it with undiluted antifreeze and let this mix with the coolant in the engine as I drive the vehicle. I realise that I may need to do this a few times to get the coolant up to the required concentration.

My question is a bit like ‘how long is a piece of string’ but, based on your experience and assuming at least one journey a day, how long would you estimate it will take for the undiluted antifreeze in the expansion vessel to be completely mixed into the rest of the coolant circuit? Also, I cannot find a figure for the coolant capacity – do you know what it should be? Robert Talbot

A The coolant capacity of the system is 6.2 litres and the expansion tank is in the main flow of the cooling system, so any coolant added into the tank will quickly be distributed around the system.

A two- or three-mile drive should see any new coolant fully disbursed into system.

However, your Meriva should be fitted with a drain tap at the bottom of the radiator which would allow you to drain off the required amount of coolant, allowing you to top up the system and correct the overall mixture in just one operation.

According to my calculations, two litres of antifreeze should restore the coolant to the recommended protection temperature. The coolant drain tap can be located at the base of the radiator, where you'll find a small outlet to which a hose can be attached, making the process quite simple.

One word of advice I would give to anyone attempting a similar operation is to not attempt to drain the system by removing the small hose on the top of the water pump. This attaches to a plastic outlet and is prone to breaking.