So the other thread is focussed on the "red" transmission. This is regarding the "blue" transmission, as in the color of the fluid.

I wanted to relate my experience if it may help any others. Have a 2015 C250 Coupe. In late 2020 (car was 5 yrs old, 40k miles) the service list in the cluster indicated #20, which is a transmission fluid change. (The indy shop even included a photo of the cluster info, so it's verified). At that time, I thought it was some sort of error, as I had understood that the blue fluid interval was 7yr/ 70k miles (which I do think some manuals out there state). However now I think the computer interval was going off a 5yr/70k mile interval, which is also posted in some manuals. I don't recall at the moment what my actual hard copy manual states, but I recall it being confusing or missing my particular transmission type.

So now more current day - car is about 9 years old, 65k miles. I knew I was past the 7 year interval, but from what I researched, I did not find any substantial recommendation to change fluid based on time alone, it seems all based on miles.

I had begun to notice at one particular road when I'd leave the house, the transmission would sort of "flare" at the exact same stretch of road whenever I had just left the house (engine was cold). This issue did not persist if the car was warmed up. It wasn't terrible, just annoyed me - felt like the car was almost in neutral for way too long before it upshifted.

So I had the fluid changed (including torque converter) and right away (as in the next time I had a cold engine and hit that one stretch of road) it was improved, but not 100% better. But a few months after, it now seems completely resolved. I don't drive the car very often as it's my wife's car.

TLDR - If I could go back, I'd change my blue fluid around 50-55k miles, which would have been 7 years for me, instead of waiting until 9yrs/65k miles. Service was about $590, including 9L of ATF and transmission filter.

 

At $590, that is certainly cheap insurance for your transmission.

If mileage and time duration are both given, then by definition, you use whichever one occurs first. For example, brake fluid change is recommended at two years with no mileage specified. The two-year interval is pretty much universal because of the tendency for brake fluid to absorb moisture (water) which leads to corrosion. To give you a reference, see below.

 

I get the whichever-comes-first thing.

For transmission fluid I couldn't find anywhere that said anything happens to transmission fluid purely based on time. So my interval would be 50k miles regardless of time.

 

Do what you want, but every 5 years means every 5 years. Apparently, fluids degrade with time once they are installed in the vehicle.


Page 18 of the attached document.

 

Since we’re tossing out anecdotes:
On our 722.9 transmissions we change fluid every 60,000 miles, which for us is about 3-4 years. Are we changing too often? Maybe. Have we ever had a transmission failure? Never. We retire vehicles at 200,000 miles or 13 years, whichever comes first.

 

I think that’s a great mileage interval. 60k is actually what my MB specialist recommended. For me it’ll take about 8-10yrs to get 50k miles on the new fluid, and that’s about the max I’d keep the car, so in all likelihood I’ll probably never change the fluid again.

 

Side note - This is why the MB maintenance guides are ridiculously confusing. If you follow that chart literally (the one you included above) notice the box is not checked (a dot actually) for the transmission service. So the 2015 service booklet is literally saying you don't ever need to change your ATF for any 2015 C-class. (And that 2015 booklet doesn't even distinguish anywhere between a W204 Coupe and W205). But if you look at a 2014 maintenance manual, it says 70,000 miles/7years for C-class W204/M271 vehicle. But apparently my vehicle computer must have been using a 5 year interval.

Again TLDR - a good interval for the blue fluid ATF (and filter) is 50k-60k miles. The "official" interval is 70k-77.5k miles.

 

i have 2011 c300 the degen mechanic from previous owner put red fluid in it. so now i got a massive shift delay on second gear shift when cold.