instead of citric flush please simply remove the drain plug from the radiator, with thermostat removed and hose connected to radiator let engine idle. Keep close watch on rusty liquid once the color change to clean water. remove the hose, shut down engine when radiator drain flood stops. use air blower over the radiator neck to further drain left over water from engine. wait for few minutes re-install the thermostat valve.
Start the engine, using coolant top up radiator intermittently till such time it starts to flood,
meanwhile wash the Reservoir bottle (aka expansion tank) with bottle brush to remove gunk, wash again with dish washing liquid, so its clean from all rust layers, do not over flood the bottle keep it at TOP MARK Level with coolant and cap it,
check for spring tension of the radiator cap, if rust or broken replace OEM NEW cap with exact same mark 0.2 / 0.9. Keep a strict watch on engine temp for few runs and check level of reservoir at cold engine only.
