It certainly sounds like it could be a blown head gasket that is allowing the car’s coolant to mix with its engine oil. A brown, oily looking fluid in the radiator is a sign that this may have occurred. Check the engine oil next. If it’s milky and discoloured, then that’s another sign of a blown head gasket. That said, just because there’s no evidence of coolant in the engine oil, doesn’t necessary mean the head gasket is intact.

So, before you rip into the engine and remove the cylinder head, make sure the gasket is actually the problem. This can be done with a chemical-based test which samples the coolant and determines whether there’s any contamination in it that can be traced to the engine’s combustion. If it’s there, then the head gasket is almost certainly faulty.

The 1989 Courier was available with a 2.0-litre diesel engine or a range of four-cylinder petrol engines ranging from 2.0 to 2.2 and even 2.6 litres in capacity. You’ll need to ascertain which engine your vehicle has and then obtain the correct workshop manual for that specific powerplant. The good news is that all these engines were relatively simple and changing a head gasket should not be too taxing for anybody with average mechanical skills.