Automotive Oil Change Monitor

An automotive dashboard monitor for oil and oil filter condition has been invented. An alternate version of it displays a percentage of remaining use before service is appropriate.

The device has red and yellow warning lights to show the need for maintenance. The circuit is very inexpensive and could be added to all new vehicles for less than $10. It is based on a common Motorola MC68HC705 computer chip, with very few extra components, and a specific software program.


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There are three conditions that the device independently monitors, that each can represent deterioration of motor oil.
  1. Actual contamination of the oil and filter due to use of the engine. This is the monitor that will normally be the dominant factor in vehicles that are driven a lot and regularly at highway speeds.
  2. Amount of elapsed time that the engine is actually operating. In city driving, consistent low speed driving can contribute acids to the motor oil, even if the contamination due to usage (above) is not such that the monitor above would be alerted.
  3. Amount of actual days (by the calendar) that have elapsed since the oil and filter had been changed. Vehicles that are driven very little often have their oil contaminated by moisture condensation inside an engine that is seldom used.

This concept was invented and Engineered by February 1998. This presentation was first placed on the Internet in July 2001.

The first of these monitors has certain details that will not be described here, but can be described to anyone who is interested in producing or marketing such a device.

In all three internal monitors, this device keeps track of the present status of that monitor and matches it against a pre-set value, to establish a percentage used up. For example, if the third (calendar) monitor was pre-set for 9 months (273 days), then at 91 days after an oil change, that monitor would determine that 91/273 or one-third or 33% of the oil's useful life had expired. Therefore, it would retain a remaining life figure of 67% for that monitor. The circuit then compares all three percentages of remaining life and determines the LOWEST of the three. If that percentage gets below 20%, the yellow light comes on. If it gets below 0%, the red light comes on.

In the alternate version, all of the above still applies, but there is an additional digital readout that continuously displays that 'lowest of the three monitors' percentage level. That feature would add about $2 to the manufacturing cost of the device.

If there is interest in manufacturing or marketing such a device, please contact me regarding the remaining details and the programming software for the Motorola chip.

This device is an invention of mine. The text on this page are protected by US Copyright laws and the preliminary paperwork related to filing a Patent on this device has been filed with the USPTO.

This invention was first designed in February 1998. It was first placed on the Internet in July 2001.

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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago