I have a 2008 Ford Escape with an inline 4-cylinder. I’ve had the car since last April and when the cold weather hit this winter (I live in Alaska) I noticed the vehicle starts to vibrate at speeds above about 50 mph. The faster I go beyond that, the higher the frequency of the vibration. It’s not a violent kind of shaking and there’s no pull on the steering wheel. However, it did not vibrate like this at high speeds during the summer. Also, on the few days when I’ve been able to park in the heated underground parking garage at my office, the car does not vibrate on my drive home. On the other hand, using the block heater when parked outside doesn’t seem to help the vibrating. I usually let the car run for a minute or two after starting it while I’m scraping the windows. Should I let it warm up even longer before driving? Is this a serious issue I should be concerned with? Will using a synthetic oil (i currently use semi-synthetic) help?
Have the tires very closely inspected for separations.
Check at a cold temp and at a warm temp and see if there are variations in the rubber structure.
The tires MAY need to be dismounted from the rims for a proper inspection.
There may be a difference in tire balance when cold or warm, I don’t know.
Find a well experienced tire man for this task.
Before you make up your mind, take the tire man with you and do a cold run first.
Go for a highway drive and warm the tires up, after the vibration starts, go back and take him out again and let him give you an opinion.
Other than that, something out of balance elsewhere could be the cause.
I think you are getting an ice and/or snow build up on the inside of your wheels that is enough to throw off your wheel balance and hence the vibration. When you parked in the heated garage the ice was warm enough long enough to melt off the wheels. When you park outside with the engine heater, the wheels stay cold and the ice stays on them.
If you are not driving to far every day, or even if you are and you use the brakes only a little the wheels may never get warm enough to melt the ice as you use the car. To get the ice off the wheels, park in a heated garage when you can or take it to a car wash and spray off the wheels. Alloy wheels have enough open space in them to do the spray technique easily, steel wheels may be more difficult to get the water into where the ice has built up.
How about rotating the front tyres to the back and back to the front. If the vibration changes, you know it involves the wheels or tyres. In cold country, you should consider the possibility that you may be getting frozen snow or ice on the wheel and it may melt off during the day at work.
How cold is it when you park the car outside? At about -15f the rubber on your tires gets too hard. This causes a flat spot. Not sure about your tires specifically but I used to live in wisconsin. One winter it was below -20 for about 5 days in a row. The car in the unheated garage got its tires so cold that for a 30 mile trip it vibrated like crazy. Could not drive over 45 mph. At those temps the tires do not really warm much. Do not worry much yet. When you have a spell of weather in the +10f and still have this issue then worry.
How about a little water in one or more tires freezing when it gets a chance. Have the tires demounted and cleaned out…External ice on the wheels could do the same thing…
I also think the tires are flat spotting - and the clue is that the problem disappears when the car is parked where it is heated. When you leave that heated garage, the tires are above the glass transition temperature, so the previous flat spot disappears. When you park in the cold with the warm tires, a new flat spot forms that can only be removed by heating the tires - and it is quite likely that the tire never get warm enough to remove that new flat spot.
I would suggest you inflate your tires a bit over what the vehicle’s tire placard says - and add more pressure to compensate for the difference in temperature between when you adjust them and the coldest temperature you are likely to encounter - 1 psi more for every 10?F.