I was in Harpers Ferry WV last week and on a couple of mornings it was snowy/icy and the temperature was in the low teens. The first morning when I started the engine, after a few seconds I heard a rattling/vibrating/rumbling sound. At first I wasn't sure it was coming from my car because several other cars were starting up around me so I turned off the engine -- the noise stopped. When I turned it back on, the noise was back, but not as loud. I thought it might have been something like the wipers trying to move but were frozen, but I didn't have the wipers on. I can only hear in one ear so I'm not good at locating the source and direction of noise, but I felt the sound was more likely to be coming from the underside or outside rather than the engine, although I didn't feel any vibration in the seat. Anyway, after I finished cleaning the snow off the car, the noise seemed to have gone away completely and I drove off with no problems. 10 minutes later when I arrived at my destination, I tried to open my window to show my ID, but all the windows were still frozen shut -- that's how cold it was. At lunch time when I restarted the engine, I heard the noise again, but not as loud. It stopped as soon as I started driving. The noise was there again when I started up the next morning, but quickly went away. What do you think could be causing this? I am going to be out there again all week and I'm a little afraid about my car having a breakdown -- although the weather is not supposed to be as cold. I never had a problem during the winter last year, but I don't think it was ever that cold.
It's probably normal. The Prius does just fine in cold weather. I'm running mine at 0F with no problems currently. It warms up fast too! But only if you're driving it.
I don't know.... many of us have started and driven our cars in single digit temps, well, at least I have and there has been no noticable "noise" from the engine. If I heard something like that, I'd take it in. It maybe even something like a mouse or squirrl making a nest under the hood, who knows? Bottom line is, that kind of unusual sound, car under warranty, be on the safe side, get it checked out. But only you can be the judge of whether or not the sound sounded bad enough to take in or not. Good luck!!
If its new check the motor oil level. Then next cold one before starting open the hood. Then start the car and as soon as possible get out of the car (make sure parking brake is on!) and listen in the engine area and see whats making the noise. Is it the engine itself or maybe coming from the Inverter (the big aluminum box on the top of the engine on the right) I bet the inverter is not happy with the single digit stuff. If its the motor and the noise is not out of hand like scraping etc just complaining cause its so cold you might want to go ahead and change the oil into a Mobil One 0-20 weight alot of people are running. Easier start up in cold weather. I live in FLA so have not experienced any cold weather yet. Today its a sunny 79 out.
Thanks for all the suggestions. Yeah, I'll definitely check under the hood the next time. I didn't do it when it happened because by the time I got all the snow and everything off it seemed to be all right. Pretty disconcerting -- especially because I was away from home and far from a dealer. It seemed to be just complaining!
Just a hunch, since your weather is typically warmer than that week, I would bet that the dealer or your oil change place used 10W30 oil (which is in spec for a Prius for warmer weather, but NOT for that cold weather), and that "after" the engine warms up, everything seems O.K. If you've got more cold weather coming, perhaps this week, get your oil changed, make sure to specify 5W30 oil, and get the filter changed, too. And yes, 5W30 can be used year-round.
It does sound like the oil is too thick. This is another reason why I do my own oil changes. The dealer and especially the Qwick Loob type places use a "bulk" oil delivered by a large truck. This mystery oil is pumped into a tote bin located either outside or in some dank corner of the shop. The obvious reason to do so is the huge cost savings over purchasing individual litre bottles of oil. You have no control over what viscosity, brand, or quality of oil is used in a bulk system. You especially have no control over what - if any - contamination control is used For example, the first oil analysis I did in my Prius, after a couple of dealer oil changes, had alarming results. After chasing a lot of dead ends, I finally managed to snag a virgin dealer oil sample. That stuff was garbage, very poor quality, and contaminated to boot I have experience with industrial process control, so I'm well aware of the steps one must take to prevent contamination of a bulk process oil system. At the top of the list is the use of a dessicator on the tank vent system I checked and the dealer had a simple inverted pipe for the vent, though it did have a screen to keep rats and mice out. All the moisture, dust, dirt, etc, was constantly being drawn into the tote bin and contaminating the oil. I've noticed the same issue at Qwik Loob type places I chose to use Mobil 1 0W-20 year round in my Prius. With up to 16,000 km oil change intervals, I've had very good used oil analysis reports. With my FJ Cruiser, it appears the 4 litre V6 is much harder on oil, in particular a conventional 5W-30 will quickly shear down I'm currently running Mobil 1 5W-20 as a winter oil in the FJ. I'll probably run Esso XD-3 0W-40 year round, as I had very good results from that oil Remember that in cold weather, oil viscosity is critical. A conventional 10W-30 should not be used in temps colder than -25 C. A conventional 5W-30 is unsuitable in temps colder than -30 C. Synthetics in those viscosity ranges should be good to -35 C or colder A 0W-40 or 0W-30 is by definition - according to the SAE J300 spec - suitable at -40 C. It is up to the manufacturer to determine the oil BPT (Borderline Pumping Temperature), which is the point the oil has a MRV viscosity of 60,000 cP or higher Mobil 1 0W-40 is rated by Mobil of having a MRV of 26,000 cP at -40, so it is entirely safe at that temperature. Mobil 1 0W-20 used to be rated 12,000 cP at the same temp, so it is clearly capable of faster cold flow If you have a choice of using a viscosity "lighter" than recommended - say a 0W-20 - or one that is marginal at the ambient temperature expected, always always err on the side of running an oil too "thin." Cold start oil flow is far more important to the motor than any possible increased wear once at operating temperature. In many cases, once the ambient temp is -25 C and colder, the motor will not reach operating temp anyway, so the lighter oil is prefered
