Electric Motor Winning? & Gas mileage dropping

Is the morning noise continuous? How long does it last?

No warning lights on the dash?

How many miles on the car? What kind of maintenance? Have you changed the transaxle oil? Spark plugs? Coolant? Checked all fluid levels?

Do you watch the state of charge of the hybrid battery on the display? Any change there? Any fan noises coming from the vent in the back seat?

The hybrid electric motor system (two motors, actually) is engaged all the time, and there aren't any "gears"--it's a continuously variable transmission. There's no clutch. The hybrid system chooses engine input based on load demand and state of battery charge. If something has changed with the battery or the engine performance, things will sound different.

 

You're due for plugs, transaxle oil, and coolant if you haven't done that. Change the PCV valve when you do the plugs, it's cheap and it's right there. Another general tuneup item is cleaning the throttle body and MAF sensor, good info here on how to do that easily.

Do you know where the brake accumulator pump is and what it sounds like? Rule that out for your noise, because there's a warranty extension on that. If you haven't flushed the brake fluid, get that done. Be sure whoever does that is Prius-knowledgeable, there are specific tools and processes.

Another common noise on cold start-up is the CHRS pump, but that should only be 15 seconds or so and when it fails it's more like a squeal. And that will be affected by old or low engine coolant.

Sometimes a failing three-way coolant control valve will give that pulsing noise. Mine went for years like that without a code or a symptom. That's near the left headlight, see if you can find the noise under the hood there.

 

Keep checking the level in the radiator daily (you can leave the black plastic cover off for the week) for the next week and top up as required with the correct Toyota SLLC or equivalent. Don't mix other brand coolants unless you are 100% sure they are compatible.

 

I have a similar situation. I drive about 600 miles every week. Including 2 long 250 mi highway trips.

It's a 2005 w/ 230k mi. The only thing I've had to replace was a bad coolant diverter valve at 178k.

This last week I experienced this unusual scenario. I drove the majority of the trip with the battery level in the Green 1 bar bellow full. The consumption level never indicated a any regeneration. My mileage was lower than usual, however, it was -1F to 6F for all of the drive. I expect poor mileage when it's this cold but this seemed lower than typical. The battery level would not drop to the Normal 3/4 bar level while driving.

No warning lights or MIL condition.

I wondering if the severe cold is primary reason for this? Or is it an indication of something else going on?

Any suggestions or firsthand experiences would be appreciated.


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