I am inclined to say it is the motor, as I have had block heater in a car and it starts ok even at 46 below. Block heaters do nothing for the battery, but I have seen battery blanket warmers.
Both really. The engine will be stiff in the cold. Both the oil will be thicker and clearances between parts tighter. So more power will be needed to crank the engine.
Cold will slow the chemical processes in the battery. So it will deliver less power.
It’s a double whammy.
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Where are you that it is 46 below ?
Describe “not start.”
I’m sure someone(s) will be sure to correct me if I’m wrong, but the clearances will be larger / looser in the cold. The metal shrinks. That actually could affect spark plug gaps nehatively if they’re on the highest side of the recommended gap range.
Grand Forks ND, -92 with wind chill it was! "“The coldest temperature we have on our record is 40 below zero which was measured in February 1996.”
Well our local news said -46 But close enough? Wife and I walked up to a corner bar just to say we did. It was exhausting. Parking lots had outlets in the apartment complex for block heaters. Blue cords that stay flexible in the cold a necessity.
I think you’re right now that I think about it again. I must have been thinking about my own clearances between joints and muscles when I wrote that!
LOL. I get that!
Luckily the car doesn’t know anything about windchill. You have to be a warm blooded mammal for that to apply.
But -46 is plenty! Welcome to the arctic. So on the no starts, what is the scoop? No crank at all? Weak crank? Or good cranking, but not firing up?
10 below, unfortunately Toyota Rav4 2 year old replacement battery was 580 cca I think . Aargh, aargh then start. WI now, ND everyone installed block heaters, 2003 Windstar and 2003 trailblazer came with one. No one local or dealer I have found that will do it
I heard you can put a frying pan under the oil pan to keep it warm… 
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Ok, cool. (Literally). But still wondering what “does not start” means…
Never said did not start, said “Aargh, aargh then start.” a quote from previous statement.
Grand Forks has never seen -92 wind chill. The coldest wind chill ever record for Grand Forks is -65F.
From the National Weather Service:
For the Grand Forks International Airport (KGFK) the coldest wind chill temperature (WCT) on record for the period from 1948 to present were on February 1st and 2nd, 1996. The coldest WCT was -65 F at 9 am CST on 2/1/1996.
I was in Montreal years ago with a late 60s Ford, when the temps dropped to -35C (-31F). No cars were starting. Those were raw temps - not wind chill.
The garages we called said they won’t even bother to come out unless the car was garaged, as they had wasted enough time with futile efforts trying to start cars.
On day 3 of the cold snap, it warmed up to -24C (-12F). And after several iterations of me:
a) putting the battery in warm water in the bathtub,
b) recharging the battery,
c) drying the flooded spark plugs on the gas stove,
d) and using more ether,
the car finally started.
Today’s thinner synthetic oils and fuel injection sure makes starting cars on cold mornings much easier.
On a different, but “cold” related note, the coldest I ever slept outside in a tent was -20F, raw temp, no wind. It was up in the White Mountains of New Hampshire several miles in on the Appalachian Trail. We were all glad when the next night’s temps only dropped to -6F.
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Batteries lose quite a lot of cranking power as they get colder. It is a chemical process that suffers when cold.
When the engine gets really cold, the current needed to crank it goes sky high because of the thick oil. High current draw and low current output is a recipe for no-start
A block heater thins the oil to reduce the starting current. A battery heater increases the cranking current available. Either may be enough to get the car started. Both most certainly will.
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I was going by the subject line of your post - you know. Where it says “car does not start.”
I know the diesel forklifts we used when I was doing the forklift and stuff thing, when the temp dropped below freezing, they were a pain to start, all had block heaters (heated coolant) but they do burn out… We would have to point the torpedo heaters directly at the engine blocks…
BTW you also had to warm up the hydraulic fluid by running the boom out and in about 10 (or 20) times or it would snap a 2" piston rod on the rear tolt cylinder on the big Lull’s if the boom was raised, the single rams weigh about 250#'s, fun job replacing by yourself… lol
No gas, we had electric 
You brought back memories of doing all the same things to get car started in 3 to 4 days continuous -26F at night warming up to -10F during the day.
One time, I had 4 or 5 slugs of frozen water come shooting out of the gas line when I disconnected it from the carb and cranked the engine.
The most desperate was exactly as you described. Removing frozen plugs to warm them in the oven and dry them out.
Go out, force door open with both hands, sit on rock hard seat, vapor from breath fogging interior and windshield, insert key and pray. The slowest RRRR-RRR-RRR turning over praying it would start. Numerous applications of starting spray. I’m surprised a rod didn’t come through the block once it started…
Ah, the good old days!
Many decades ago I helped a professor doing some research in Massena NYfor a couple weeks in feb. Some mornings it was -50. My professor had visited there many times in the winter doing research and was ready for it. Every evening he’d drain the oil out of his truck and bring it inside. Then in the morning pour the warm oil back in. This was before multi-viscosity oils were in wide use. He learned that trick from the locals.
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Wouldn’t an engine oil heater be easier?
In my youth I’d bring the car battery into the house on really cold nights. That did the trick for me.