The anti-freeze on my '99 Mustang Cobra 4.6 litre DOHC had not been changed since new, so I set out to change it. Draining the radiator and removing the drain plug from the driver's side of the block went well. But the drain plug on the passenger side of the block is in a tight little spot up behind the motor mount and inaccessible to any wrench I've ever known. Not wanting to tackle removing the motor mount or the starter, I refilled the engine with new anti-freeze. I drained about 10 litres, while the system has a capacity of 13.3 litres.
My questions are: Is draining and replacing three quarters of the anti-freeze good enough to renew anti-corrosion protection?
Next time, how would I go about removing that hidden drain plug?