The Challenge in Using Mileage for Oil Change

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Much like Idiot’s Lights, every car on sale today comes with a period which, according to the manufacturer, engine oil needs to be changed.

For my daily driver, this is 5k miles.

However, as I sat in traffic today with the vehicle idling for many minutes, a thought struck me: this engine oil change metric is dumb — and is likely to cause more harm than good, if you live or commute in traffic-prone zones or generally, idle your engine a lot.

This is how it pans out.

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5k Miles Means 5k Miles Driving on The Road!

The concept of 5k miles for oil changes means 5k miles when the vehicle moves, which makes sense (at least, on face value).

This is why, in the owner’s manual, there’s an express injunction to start the vehicle, engage it in drive, and start driving, almost immediately, being careful only to make certain that you don’t push it hard when still cold.

The logic, as can be seen, is simple: the manufacturer is eager to avoid raking up time not covered by the actual movement (which is likely to be missed).

However, this only mitigates the issue, as it is — it doesn’t completely solve the problem.

So, if it doesn’t, what does?

Do Not Change Your Engine Oil According to Mileage: Do This Instead

Instead of relying on good old mileage to change your engine oil, switch to Engine Time (E/T) — which is a record of how long the engine has been on in a cycle. 

What this little counter on the instrument cluster does is that once the engine fires up, it starts counting and whether or not you move, it continues its duties, so far as the engine remains on.

This makes perfect sense since engine oil keeps circulating and never stops, even when you idle or are stuck up in traffic.

How to Keep Track of Engine Time as an Oil Change Indicator

As much as keeping track of engine time as an oil change indicator is preferred to miles logged, it is much more challenging to keep this metric and tally things up.

This is for the following reasons:

1. Most older vehicles do NOT have this function.
2. This is a temporary memory-based metric; anything that plays with the starter battery distorts it.
3. Once it reaches 99 hours, it resets back to 01.

To avoid these challenges, assuming your vehicle has this function, simply log things down once ‘99’ is hit and a reset occurs, and then, tally everything up at the weekend — or month-end, whichever is preferred. 

Some other vehicles, such as the modern Hondas, have a sort of engine oil ‘health’.

This system uses a myriad set of metrics to determine when your engine oil is due — and this includes miles logged.

Interestingly, one of the metrics used for this purpose also includes the time the vehicle remains ‘online’, E/T (engine time) as this ‘health’ depletes even when the vehicle is stationary.

If you use a modern Honda, you don’t need to bother with either your mileage or engine time: just stick to the recommendation and you’ll be fine.

How Many Miles Is an ‘Hour’ in Engine Time?

There’s another challenge that presents itself with this system of relying on engine time to change engine oil and not mileage covered: how many miles is an hour?

This is challenging — but largely depends on your driving reality.

If you drive in a busy city exclusively and idle a lot, an hour translates to 20–40 miles with an average of 30 miles.

If you drive exclusively on the freeway, an hour translates to 60–80 miles with an average of 70 miles.

If you do a healthy mix of city and highway driving, an hour translates to 40–60 miles with an average of 50 miles.

Note that the above are fair estimates that may vary widely, depending on your unique case and driving habits so this should be taken for what it is: fair estimates.

So, assuming you drive a healthy dose of city and highway driving, 5,000 miles (suggested OCI interval)/50 miles (average miles covered in an hour of E/T) = 100 hours of engine time (E/T).

In such a condition, changing your engine oil should be done at 100 hours (or six months — assuming this is what your manufacturer recommends), whichever is first.

What About the Time Factor?

Once in an engine, engine oil degrades — whether used or not. 

For this reason, it makes sense that the six-month interval (or whatever your manufacturer recommends) be held sacred.

If you’re interested in pushing this time forward, be sure to get special engine oil that permits this reality, such as an extended-performance brand like Mobil 1.

Conclusion

The process of logging your E/T manually to determine when your oil change period is due is superior to the conventional system of relying on mileage in the sense that it (actually) covers the time the vehicle is on — not just when it is moving (something the ‘mileage system’ does not). 

This accounts for idling and traffic situations, situations that are very hard on the engine and unfortunately, are not conventionally considered when the business of changing engine oil comes up.

Don’t fool yourself, however: manually logging your E/T is hard work and requires some level of dedication for it to work.

However, if you’re serious about making sure that your engine lasts the longest, then, this method is a no—brainer.