Coolant Change Kills Corrosion Problems

Almost all automotive manufacturers recommend replacing or changing a car's antifreeze or coolant at some regular interval. For most Jaguars, this is to be done every two years regardless of mileage. Why is this important? Since the XK engine was introduced in 1948, Jaguar engines have been bi-metallic, i.e., composed of both aluminum and cast iron, usually in the form of an aluminum cylinder head and an iron block. When two metals of sufficiently different electrochemical potentials are in contact, either directly or through an electrolyte (such as water or antifreeze), significant corrosion will occur over time. Modern antifreezes contain a corrosion inhibitor which reduces this problem. However, this anti-corrosion additive becomes depleted with use and this is why the antifreeze needs to be replaced every few years. It also is why one doesn't want to use plain water in the cooling system.

It is fairly common on Jaguar engines which have not had the coolant renewed regularly to have cylinder head studs corrode completely in two, usually at the lower end of the studs where they thread into the top of the main bearing web. In many cases, this cannot be repaired economically. Additionally, as the six-cylinder XK head does not pilot tightly on the head studs, coolant flows between the stud and the hole in the head. In many cases, with neglected antifreeze servicing, it will be extremely difficult (or impossible!) to remove the cylinder head due to corrosion between the head and the studs.

The bottom line: replace your car's antifreeze every two years with any quality brand labeled as "Alugard" or "for Aluminum or Bi-Metallic engines." As the man in the oil filter commercials says, you can pay a little now or a lot later.