On my 1997 4Runner, I have noticed something since I've moved from the deep South to upsate NY. When we get particularly cold days, single digits or below, I'm having a loss of power brakes for about the first
30 seconds of using the car. The brake pedal hardly depresses at all, and it takes a very strong pressure l to stop the car. After pumping it for a bit, things seem to normalize and work OK. This is worrying for 2 reasons; if it occurs at another time, it would be BAD, and if someone borrows the car, they may not expect it. The reservoir is full and the car is regularly maintained. Can someone advise?