Engine failures and oil change intervals - data from Polish workshops

[NRohirrim]

Hi.

I went to my colleague, who owns 2 workshops, and gathers a lot of data about cars that are repaired by him and his crew. I made a small graph based on this data.
Entry points: 195 cars, 2 - 26 years old that arrived with major engine failures between 2013 - 2024 (I could collect more data up to year 2005, but I wanted to focus on more modern cars that used more modern oils).
Data is gathered precisely by him, since he has a policy that he gives discounts for his services, but only if the oil is changed in his workshop before every 10 000 km* / 12 months*, whichever comes first (and he also gives warranty for rebuilding engines by him / warranty for labor for putting new engine for another 100k km (62k mi) / 3 years, but only if oil later is changed before every 8000 km** / 8 months**).

Major engine failures in the cars below 200k km (125k mi) driven, with reported oil change intervals:
- over 15k km (9k mi) - 72% (16 cars)
- 10k - 15k km (6k - 9k mi) - 14% (3 cars)
- below 10k km (6k mi) - 14% (3 cars)

Failures in cars that drove 200k - 400k km (125k - 250k mi) with reported oci:
- over 15k km (9k mi) - 62% (94 cars)
- 10k - 15k km (6k - 9k mi) - 27% (41 cars)
- below 10k km (6k - 9k mi) - 11% (16 cars)

Failures in cars with over 400k km (250k mi) driven with reported oci:
- over 15k km (9k mi) - 14% (3 cars)
- 10k - 15k km (6k - 9k mi) - 59% (13 cars)
- below 10k km (6k mi) - 27% (6 cars)

*in the case of full synthetic; in the case of synthetic blend - 7500 km / 9 months
**in the case of full synthetic; in the case of synthetic blend - 6000 km / 6 months

 

[fantastic]

First thing I notice...
Over 15k km under <125k have the highest engine out of your 3 brackets (<125k, 125-250, >250k)
but then...
10-15k km greater than >250k have higher engine failures the higher the mileage out of your 3 brackets (<125k, 125-250, >250k)
Lastly...
10k km & below between 200-400k are higher engine failures the higher the mileage except for the lowest mileage <125k

Interesting data none the less. Thanks for sharing your local shops data.

 

[Jetronic]

First thing I notice...
Over 15k km under <125k have the highest engine out of your 3 brackets (<125k, 125-250, >250k)
but then...
10-15k km greater than >250k have higher engine failures the higher the mileage out of your 3 brackets (<125k, 125-250, >250k)
Lastly...
10k km & below between 200-400k are higher engine failures the higher the mileage except for the lowest mileage <125k

Interesting data none the less. Thanks for sharing your local shops data.

the shorter oci are overrepresented at higher mileage, because the long oci never made it there, they died before

 

[dbias]

the shorter oci are overrepresented at higher mileage, because the long oci never made it there, they died before

Exactly. Survivor bias.

 

[NRohirrim]

Indeed. Cars that have changed their oil less often than at least every 9k mi (15k km) very rarely make to over 250k miles (400k km).

 

[LongTime_Lurker]

It’s impressive that this shop collected so much data over this period. There is always the bugbear of correlation vs causation and lurking variables that we don’t see or have control over. I would be curious to know whether the individuals that went with the shorter service intervals have a different mindset or approach towards vehicle care in general.