The coolant on this vehicle was a suspicious rusty brown color and of unknown age and composition so I drained it, flushed with a chemical cleaner and refilled with known high-quality coolant. This has to be done with a cool engine, of course, to avoid getting burned or sprayed with hot fluid.
Brown color could be from mixing different brands of antifreeze or could be caused by corrosion inside the cooling system. Volvo 850s have an aluminum engine block and aluminum radiator so there is not much iron in the system to rust. At any rate, the color and some mineralization evident from the thermostat replacement plus the uncertain age and quality of the coolant demand a good flush and fill.
The 850 radiator has no pressure cap to directly access the radiator; everything is done through the plastic coolant expansion tank:
Start by raising the front of the car and supporting securely on jack stands. Remove the splash guard under the radiator:
Place a catch pan under the radiator drain cock on the driver side (LH) and open the drain port:
Removing the coolant reservoir cap allows air to get in to drain smoothly. This car had an after-market radiator installed at some point, evident by the drain plug being different in size and type from a real Volvo part. It also looks newer than the rest of the car. I measured around 5 quarts from the radiator.
After draining the radiator, replace the drain plug and crack open the engine block drain plug accessed from underneath behind the engine towards the passenger (RH) side:
Coolant from the engine drain splashes all over the place so you need a large pan to capture it all. Better yet, stick a hose over the port to direct the coolant into a catch pan, which I didn’t do out of laziness. Didn’t get much coolant out of the engine block but it was good to drain out what was there.
Did this job along with the thermostat replacement (#58). At this point the thermostat was removed and the housing re-attached so flushing could occur with no thermostat in the way.
After tightening the engine drain plug, I added some Prestone super flush chemical to the reservoir, then filled with distilled water.
As mentioned in the previous thermostat topic, it is important to use only high-quality low-mineral content water in the cooling system. Mineral buildup causes chemical reactions and gums up the innards.
Closed up the reservoir and ran the engine for 10-15 minutes to get it all circulating through the radiator, engine block and heater core (put cabin temp controls on heat). That should effectively break up any gunk and rust and minerals in the cooling loop.
Waited for the car to cool down, then drained as before. After that, I refilled with distilled water only and ran the engine again to get one more good flush with no chemicals. Drained once more after cool-down. This is where I installed the new thermostat.
Now the car is ready for fresh coolant. Something so simple can be so controversial. Lots of discussion about best or proper coolant for Volvo 850s. Many people insist only real Volvo coolant should be used, or at least a particular alternative. Others say just use whatever. Strong opinions all around and much of it contradictory. I weighed opinions from reputable forum comments and decided to go with extended life coolant from a major supplier, Prestone for this job.
Mixed half coolant and half distilled water and filled the reservoir for the proper 50/50 ratio. Ran the engine until it got warm and then topped off the reservoir to keep it level. Also added more after it cooled off completely.
Of course after draining I re-attached the splash guard. Also disposed of used coolant properly, not into the sewer.
Cooling system should now be good for a few years at least, with a new thermostat and fresh, high-quality coolant after flushing.
$4 Flush, $13 Coolant, $4 Distilled Water
Coolant in the car is normally a mixture of coolant solution and water. Water is the primary ingredient and in some warm climates is all that some people run in their cars. Coolant keeps the water from freezing in cold climates, which is why many people call it anti-freeze. By an interesting property of chemistry it also raises the boiling point of the water (so does the pressurized cooling system), so coolant helps in both cold and hot weather. To call it just anti-freeze is not accurate; it is also coolant and the product you buy says both on the bottle.
Coolant also lubricates the water pump so if the fluid goes bad it can cause problems for the pump.
Extended life coolant adds corrosion-resistant chemicals which allow it to last up to five years, although many people change it more often than that.