Coolant Change Guidance - Volvo Penta 2003

[Ex-Calif]

It helps to read the book and know how much coolant capacity you have + anything added on like water heater.

If you haven't put that much coolant in is air in there and you aren't done.

[Neptune's Gear]

Others have given you good advice.
I have a 2003T, and have used these engines for nearly 15 years and 9500 hours. Here is my advice for this engine.
Flush with fresh water until it runs clear. Also, if it the 2003T model (maybe on the others as well, can't remember), there is a plug in the exhaust riser that comes from the head, just above where the tube from the thermostat goes in. That plug is an air bleed. Take it out, and fill until water/coolant comes out of there. Otherwise it will not be full, and will run with a hot spot there.

If the maintenance schedule is unknown, remove and mechanically clean the heat exchanger, and the oil cooler (behind the heat exchanger). a .22 cal rifle cleaning brush works well. Make sure that inside the tube between the thermostat and exhaust - there is a plastic insert with a small hole in it - it blocks easily - clean it out. Change the raw water impellor. Any one of these things can/will cause overheating.
When it's in bits, go to the volvo dealer and get some of the cooling system sealing rings - both the flat one, and the one with the groove in the center. You can bet that without some new ones, the cooling system will leak when reassembled. They are cheap, and can save lots of frustration!
If the engine is in good nic, they work well, although normally a bit smoky when cold.