When considering buying a car on Ebay do not ever make an impulse buy.. It will surely end in disaster.
When a car is described as "good for its age" it means it has faults that are not detailed.
When a seller informs you upon being specifically asked if the vehicle's cooling system is free from fault that it is ok and in good order, then it should mean just that. Do not be afraid of asking the seller what their trade or proffession is, if they are a knowledgeable person who is from the motor trade then their description of "free from fault or ok" is admissable in court should the car fail to perform its normally expected duty.
Should the vehicle fail within a very short time period of collecting it, contact the seller immediately and ask them what they are going to do about it? Their stock in trade answer will be "it was sold as seen mate and what do you expect it to perform like its X years old" This is not an answer that you should simply accept! The protection of the Sale Of Goods Act 1973 covers your rights and the item sold should perform its reasonably expected duty cycle. It should "Do what it says on the tin".
Ask the seller is this their final answer on the matter?
Always correspond in text format never verbal.
Always keep the question and answer correspondance.
Do not be afraid to turn to the courts for an answer.