While nearly everyone knows that you’re supposed to change your car’s engine oil every 3,000 to 5,000 miles (or even more in the case of some newer cars), not everyone knows that you’re supposed to change your Jaguar’s coolant/antifreeze at regular intervals, too. Nearly every auto manufacturer has their own recommendations for how often this should be done, when it comes to classic Jaguars, we recommend doing it at least once every two years.
So, why is this important? Many people go years without changing out their coolant and their cars run just fine, so why can’t you do that with your Jaguar?
Since the XK-series engine was introduced in 1948, most Jaguar engines have been built with cast iron blocks and aluminum cylinder heads. This is a common practice nowadays, as the iron blocks tend to be more durable while the aluminum heads are lighter and more efficient. However, the disadvantage of this setup is that iron and aluminum react differently in the presence of an electrolytic fluid such as antifreeze. Because of this, corrosion tends to occur where the block and heads are in close proximity to one another—at the head gasket. Fortunately, nearly all antifreeze that you purchase at local auto parts stores contain corrosion inhibitors in them that helps to prevent this from occurring. However, these inhibitors are consumed with time and use, so while the coolant is still capable to help regulate the engine’s temperature for many years, its ability to prevent corrosion is greatly diminished.
This is an especially common problem in vintage Jaguars that may not be driven on a regular basis. Cars that aren’t subject to regular use and only have been driven a few thousand miles over a multiyear time span might have coolant that looks to be nearly new and won’t get changed for several years. Unfortunately, this often results in a significant amount of corrosion inside the engine, and specifically around the head studs. 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. 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.
Bottom line: Replacing your Jaguar’s engine coolant once every two years is a cheap way to safeguard against major engine repairs in the future.