Glad you found the mistake before it bit you.

Coolant loss and overheating have killed a lot of Volvo red blocks.

There is mention in the FAQ's about making up and installing a low coolant sensor circuit in these cars. It is nothing more than a float switch connected to a warning light in the dash area. If the coolant level in the reservoir drops down the light comes on. Even a catastrophic coolant loss is signaled before the engine can overheat.

All of our Volvos have had this sensor installed and it has warned us twice of coolant losses that had the potential to lead very quickly to overheating; once a ruptured heater hose and another a ruptured turbo coolant hose. Both instances had happy endings because of the early warnings.

Randy