I just purchased a used 2015 Prius C 104k miles and whenever I accelerate, I hear a faint rumbling sound from the engine. I hear it around 30-50mph. Could this be due to the cold New England weather? Also, I found it not as zippy as my 2013 Prius C in terms of acceleration. However, my 2013 never saw cold weather while it’s entire life was in Los Angeles. Could it possibly be a soon to be failed transaxle? I changed the cabin/engine filter and new oil. I’m getting the inverter/engine coolant, brake flush and transaxle fluid done. If the issue persists, could be it something more serious?
Transaxle failure is pretty darn rare in these. Toyota does not have a replacement guideline for the fluid in there- they say it's good for life. I think they might be right, personally. If you do decide to have it changed, make certain they use genuine Toyota WS fluid; accept no substitute. Are you certain that the noise is from the engine? You might try changing the monitor screen to show you when the engine is actually running, that might help you eliminate noise sources. Mostly a wild guess, but perhaps check on the wheel bearings. They can be a major source of noise and you could have one or more worn out by 104k. Toyota changed very little between the 2013 and 2015 model years, so it might be tricky to nail down the performance difference. That said, someone could've accidentally installed the wrong tire size on one of these cars and that alone would make a difference. Check the battery cooling fan under the left rear seat. Make sure it isn't blocked or full of pet hair or dust. There are several youtube videos that show how to gain access and clean it with an ordinary vacuum cleaner.
I had the brake fluid, inverter and engine coolant, oil change, both air filters, hybrid fan cleaned, spark plugs, and transaxle fluid all done. I no longer hear a any strange noises. It could have been the engine air filter as it was extremely dirty.
If i'm right, as far as i know, there has been no reported cases of transaxle failure on the Toyota Prius C.
Just keep it in perspective: Toyota has produced about 1.5 million Aqua/Prius c cars, but there are only a few thousand owners signed up on priuschat and far fewer are active today. So in the grand scheme of things, our sample size is too small to matter.
