We Dug Into A Tesla Model 3 And Chevy Bolt To Learn Their Secrets

If you still don’t believe that electric cars are, at the very least, going to be a big part of our automotive future, then, well, I suppose have fun in your beautiful gasoline-soaked fantasy life. If you’re like most everyone else with eyes and brains, you know EVs are here to stay, and it makes sense to get to know them, deep down. That’s why when we heard that we could get access to three of the most popular EVs on the market, all torn down into their constituent bits, we knew we had to take advantage of this opportunity. And boy, did we.

The place that took these three cars — a Chevy Bolt, a BMW i3, and a Tesla Model 3—and so completely and carefully dismembered them is Munro, the engineering firm that major automakers turn to when they want to know exactly how their competitors are building cars, right down the last, tiny bolt and screw.

The three EVs that we had access to are an especially good selection, because they each represent a very different approach to building EVs. Of course, in an ideal world, we’d have had access to a few more. The Nissan Leaf, for example, may be the most common battery-electric vehicle on the road, so one of those would have been nice. The good news is that in general design and construction, I think the Leaf most resembles the Bolt, so it’s not like it would constitute an entirely separate category.

Also, it’d be great if we had access to a Volkswagen MEB platform, but since those aren’t available yet, I can’t really be too upset it wasn’t there. I think that new platform is quite similar to Tesla’s, but perhaps with a bit less tight integration of components, which means the VW platform by default doesn’t include a frunk (I think it’s possible it could, and the ID Buzz certainly shows it doesn’t need much of a hood) but could offer some improvements when it comes to serviceability over the Tesla platform.

I’m just speculating, of course. For the Bolt, Model 3, and i3, though, we didn’t need to speculate at all, since we could see everything. In fact we saw so much that our video editors made us dial back the intense geekery in some of the video, but I’m going to hand off to David to give you some really, really deep-dive stuff we couldn’t cram into the video, for sanity reasons.

David Tracy:

I won’t really get into too deep detail, as this is really just a high-level look at some of the differences between these three electric cars (ok, so the i3 is technically a hybrid since it has the range extender), but I will point out some of the fun things we saw but didn’t include in the video.

I’ve already made it clear how much I like cooling systems, and one thing we talk about in the video is how the i3 utilises a direct refrigerant cooling setup for the batteries, and the Model 3 and Bolt both send liquid glycol-based coolant into their battery packs. It is worth noting, though, that the Model 3 and Bolt also make use of refrigerant in what’s called a “chiller,” which is hooked up to the HVAC system.

Such a setup means the Bolt and Model 3's batteries are actively cooled, rather than passively cooled as would be the case if they just sent liquid glycol through a radiator at the front of the car. You can see the Model 3's liquid coolant-to-refrigerant chiller in this cooling system diagram, which I explained before in another post.

And here’s a look at the Bolt’s chiller, where refrigerant absorbs heat from liquid glycol that has passed through and absorbed heat from a heat exchanger in the battery pack:

The different ways that the vehicles warm coolant for the batteries is also quite interesting. According to Munro, Tesla uses a coolant-to-oil heat exchanger (shown below) on the drive unit for this task, actually “stalling” the motor to intentionally create heat in the oil—heat that then gets transferred to the coolant and ultimately to the batteries.

By contrast, the BMW i3 has little resistance elements on the base of the battery pack, just under the thin refrigerant-containing rectangular pipes that sit under the battery modules. You can see the full setup in this video, but here’s a look at the part of the system I put together on a desk at Munro:

Here’s a closer look (resistance heater on the left, refrigerant pipe on the right):

The Chevy Bolt is like the BMW in that it uses a dedicated high voltage resistance heater to warm up the batteries, except instead of sitting inside the battery pack, it’s a separate unit, and warms the liquid glycol coolant that goes into the battery (which contains pouch-style cells, which are known for their tight packaging advantages). The Bolt’s high voltage battery heater is shown on the right:

On the left in the image above is another high-voltage “PTC” (positive temperature coefficient) heater, which, like the battery heater, is essentially a heat exchanger between an electric resistance element and coolant.

Interestingly, the Bolt (and I believe 2014 i3 range extender model we looked at) use these high-voltage resistance heaters to pump heat into liquid coolant, which then gets sent to a heater core in the cabin just like one you might find in a standard vehicle with an internal combustion engine. (Fully BEV i3s, I’ve read, use heat pumps, which I described a bit in another article).

The Tesla Model 3, though, forgoes the liquid coolant, and just sends current to heating elements built into the in-cabin “heater core”:

Another difference Munro pointed out was that the Bolt and i3 use parking pawls as part of their gearboxes. These are essentially mechanical “locks” that keep a vehicle from moving when in “park.”

Here’s the i3's:

Here’s the Bolt’s inside part of its gearbox:

Munro says the Tesla Model 3 does not use a parking pawl, but rather relies on its electric park brake mechanism to keep the vehicle at rest when parked:

These are just a couple of the many, many differences we observed between three of the most popular EVs while at Munro & Associates — but weirdly, if you want to know which car is “better”, you’ll just have to drive one.

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