I had no problem but decided to do an all fluids change including oil, and hygroscopic bake fluid. Vacuum through the dipstick did a good half on gearbox then replace with recommended. Loosened bottom hose OUT with engine running, heater matrix wide open, fan full belt and hose pipe at the same rate IN did the job. It looked like Heinz main course soup - lots of square carrots - do NOT back-flush alloy rads !