Aigh! I even forgot tranny fluid.
Since late models have synthetic ATF... it is questionable... I suppose like
15000 miles as suggested in Mercedes Maintenace schedule. That is almost 7 years at
The idea is to keep a simple interval based on mileage/time.
Engine oil is no choice but every year.
All other fluids can be changed at say evey 5 years.... Once every half decade is good rule of thumb and easy to remember.
Some fluid will almost never be changed... like how many of you every changed differential fluid? Differential fluid last like 100,000 miles... or Amsoil say 50,000 miles... but at 2500 miles a year, it will take good 40 or
20 years before you get to it... I supposed 10 years is enough for differential fluid.
You just need to create your own 'maintenace' schedule. Even I don't drive much these days... and synthetic fluids are expensive. It is not to say that synthetic is not worth it... it definitely is worth it.... change oil once a year (10K miles) instead of 2, 3. or even 4 times a year dino.
The whole key is NOT to waste the resource... why throw away oil when you don't have to. It is still good to use.
This is where oil analysis laboratory comes in. I never used it but I can see how it can save you money and time over long haul... why throw away your money when you don't have to.
If you only have one or two cars, it is like I could just use that money to buy more fluids. If you maintain 5 cars, those money is huge. at $7 to $10 a quart and times 5 cars and number of bottles you need.... whoa.
Hope these insights helps.