All the fluids in your Capri should be checked during the service. The cooling system is often neglected. I recommend using a 50 : 50 mix of anti-freeze / water year round. Make sure that the anti-freeze you buy is 'full strength' and not just summer coolant. This is just anti-freeze already watered down and why pay good money for water when it comes out of your tap for free? The anti-freeze must contain corrosion inhibitor. Do not be tempted to mix your own concoction using ethylene glycol as this will not prevent corrosion. I recommend you buy an anti-freeze tester. Don't pay more than £2 for one of these as the simple ones work fine. Top up the expansion tank to the cold fill level if necessary.
It is worth keeping an eye on the coolant level. If you are constantly topping it up and there is no sign of a leak anywhere, then this may be an indication of a blown cylinder head gasket. You should also consider changing the cooling fluid every two years. This is easy to do: simply undo the jubilee clip on the bottom hose of the radiator and pull the hose off. Let the fluid drain out fully. For a complete drain, there is also a plug on the engine block. It is located just below the exhaust manifold on the side of the engine and looks like a bolt. Undo this and another pint of fluid will gush out. If you splash any of the fluid on your car, was off with cold water as anti-freeze and paint don't mix!
It is a good idea to have a hose pipe handy so you can flush some clean water through the radiator. Replace the plug and bottom hose and fill with a new 50 : 50 mix using the radiator cap entrance, not the expansion tank. A useful tip here is to start the engine up and allow it to come up to temperature whilst topping up the radiator. As the thermostat opens, the level in the radiator will drop again. By the end, the coolant should be up to the brim of the radiator cap.