Hello,
Draining a coolant system completely and flushing the system is not a very complex effort in my experience. One just needs knowledge about the location of various parts in that perticular vehicle.
I have done complete coolant flushes on my 91 Prado and 2004 BMW 545i.
The cooling systems are basically the same in all vehicles so, is the basic draining/filling process.
On Both vehicles , there are drain nuts on the lower side of radiator and at the engine block. Just remove them and the old coolant drains out.
at this point you can detach a few rubber hoses especially at the heater core side and run water from your garden hose through the system, you can also do backflushing i.e. run water the other way to help get the crap out. Make sure the heater valve/switch is on i.e. in hot position during the full procedure.
Maybe use some compressed air to get the remaining tap water out.
attach all hoses and tighten all bolts. And then fill with a mixture of 40-60% coolant diluted with de-ionized water. Use of proper coolant is important, although now there are universal coolants available.
Start the car and purge the system of air according to manufecturer's suggestions.
Keep monitoring the level after every driving cycle when the vehicle has cooled down i.e. morning before going to work.
It took me about 3-4 hours to so this and i also changed the thermostat(went 10'F cooler) new rad cap etc, new heater hoses). as long as you have access to basic sockets/tools and you/your mechanic can access/loosen tighten the drain correctly, you should be OK.
Thanks and take care.
