Which is correct, Preventive or Preventative maintenance?

This car could have used a little more TLC.

There are a number of language experts who see a decline in the quality of our language due to things like texting and the internet. This problem of misusing language, however, precedes the digital age. In various parts of the country people say they will borrow you a dollar when they mean lend. Other words frequently mixed up include accept and except, principal and principle, stationary and stationery, and a host of others.

So what is it when we come to preventive maintenance. In many places we see preventative maintenance, and in others it is the shorter preventive.

According to Wikipedia (with a disclaimer that the article needs verification for accuracy) the proper word is preventive maintenance.

Preventive maintenance (PM) has the following meanings:

1. The care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.

2. Maintenance, including tests, measurements, adjustments, and parts replacement, performed specifically to prevent faults from occurring. 

The primary goal of maintenance is to avoid or mitigate the consequences of failure of equipment. This may be by preventing the failure before it actually occurs which Planned Maintenance and Condition Based Maintenance help to achieve. It is designed to preserve and restore equipment reliability by replacing worn components before they actually fail. Preventive maintenance activities include partial or complete overhauls at specified periods, oil changes, lubrication and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn parts before they cause system failure. The ideal preventive maintenance program would prevent all equipment failure before it occurs.[citation needed]

There is a controversy of sorts regarding the propriety of the usage “preventative."

In point of fact, whatever you call it, the real question is, are you doing it? Routine checking of fluid levels and tire pressure are just two of the responsibilities that come with owning a car or truck. The best way we know to make sure you change your oil at proper intervals is to park your maintenance information in MyAMSOILGarage. You can store maintenance for all your vehicles in one location, get product recommendations and email reminders that it's about that time.  Best of all, it's free.