Loud noise from ICE when first driving in cool/cold weather.

probably the inverter, happens from time to time.

 

Check the oil in engine and inverter. H

 

My 2006 started doing the same thing last winter. Kind of a screech/whine when accelerating when the temperature is below 50F or so. It stops if I back off the throttle a little. It goes away after I've driven for a few minutes. It seems louder and lasts longer the colder it is outside, which isn't surprising.

I had the water pump and belt replaced some time ago, but I don't think this started right after that. Plenty of coolant in the inverter and oil in the engine.

Now that summer is almost over I'm assuming this will start again, so any help figuring it out would be greatly appreciated.

 

I've noticed this too in the last month when started below 50F. I did have the recall on the water pump completed but I don't believe that's where the noise is coming from; it sounds like it is from the passenger side and increases with ICE acceleration and then subsides within a couple miles, but always less than 3 minutes. I thought perhaps my oil filter was placing excess pressure on the oil pump when it is cold because this is a 15,000 mile oil change interval with 12,000 miles on the filter (Mobil Extended Performance 5W-30 and a 15,000 mile filter). I just changed the filter only tonight, so tomorrow morning will tell. I very much doubt that this is the issue because I doubt the Prius can create enough dirt to clog a filter in 12,000 miles. The car has 110,000 miles, inverter coolant level is fine as is the oil level.
I'm surprised we don't see more posts on this.

 

Is it possible that the serpentine belt is slightly loose? It should deflect ~0.5" when 22 lb of pressure is applied at a point midway between the crankshaft pulley and idler pulley (the longest belt run).

 

Thanks Patrick! I was mulling that this morning as the noise was there on startup this 29F morning and, as the previous posters stated, both had recently changed serpentines; I also had changed mine 12,000 miles ago when it was warm. I'll check that next.

 

Thanks, Patrick. That was it. The belt didn't feel that tight, so I tightened the tensioner a third to a half turn. The sound has not come back in the past two very cold mornings.

I still can't believe that's all it was. I guess I've never heard a serpentine belt slip. It sounded nothing like the familiar squeal of a loose v-belt.