Thanks. I just wanted to ensure Puyapim and I had the same understanding as to what a harmonic imbalance is given his statement. It's been a few years since I took advanced dynamics in university so granted I'm a bit rusty, but like yourself I don't see how harmonic imbalance or vibration could be induced by cold temperatures.
My background is in engineering so I know where your coming from.
Over the years, car manufacturers have used different materials to soften vibration to the cabin and within the cabin.
From my experience working on cars since the 90s to now,
outside the cabin, outside the car,the dominate material used is a rubber base or something very similar. You would have these at most spots where one piece needs to move freely from another, but still be attached.
Examples,
engine -> body,
transmission -> body,
exhaust -> body,
suspension/differentials -> body,
suspension arms -> body, plus many others.
In cold temperatures it's naturally stiffer and would transmit more vibration to the cabin. Rubber base materials naturally break down with heat cycles, exposure to chemicals that break it down, and just age.
My experience with changing rubber bushings.
Older cars that we used to convert to dedicated race cars would have aged rubber bushings that created problems(another topic). We'd replace all of them with solid bushings or a much stiffer, less flexible, material than OEM. Usually we used Polyurethane so there's "some" vibration dampening and memory.
We got a better feel of the road (desired), but much more vibration was transmitted to the cabin from everywhere(less desired).
In the last 5-10yrs, there has been some impressive advancements in creating a quiet cabin and I imagine they've gone beyond the OEM rubber base material to more exotic materials or creative construction.
I had no clue Mazda used liquid filled bushings between the engine and body(which sounds great, but expensive).
If the claim is that it "freezes", then I predict it actually becomes solid (not just thick) under extreme conditions and that WILL transmit a LOT of vibration to the cabin. My guess is that what ever liquid they do use
I'm curious as to what the "band-aid", short-term solution would be and what technology other car manufactures use that are exposed to extreme colds (Alaska, Canada, Sweden, Finland, etc).
100% of the time, materials that work well between extreme hot and cold temperatures, increase in cost astronomically, if it's even possible. Usually it's more cost effective to use different materials for different environments.
I predict they will do a voluntary recall, or bulletin to the techs to replace/add blah-blah for people who have complaints, and then for the 2020 or next generation model, there's a different material for Canadian built cars with a higher price tag. I would be really impressed if a solution was already integrated into the 2019 model year truck.
Perhaps, the supplier who designed, built, and sold the liquid filled bushing to Mazda promised it reduces harmonics by xx% minimum from yy deg F/C to zz deg F/C and internally where they assemble it, Joe Assembler hates his job or is pissed at his manager didn't do his job to what the instructions say, "because it'll will work fine", "those stupid engineers don't know what they are doing", "Reduce my benefits/retirement? Screw you guys".
Therefore it's only a batch of bushings that are out of tolerance and not a poor design.