Can I use my existing 3-prong dryer outlet (NEMA 10-30) for EV charging?

Short answer: you can adapt it, but not at the full 30A. Continuous loads, which EV charging is since it's hours at a steady draw, are supposed to stay at 80% of the breaker rating, so a 30A breaker gets you to 24A continuous, not 30A. The bigger issue isn't the amperage though, it's that a 10-30 has no separate ground: the neutral and ground are the same conductor at that outlet, which was legal when your house was built but wouldn't pass inspection on a new circuit today. It'll work. Whether it's the setup I'd want long-term is a separate question.

Been running a Tesla 10-30 adapter off my old dryer outlet for about three years now, derated the same way quietwalrus described. No trips, no warm plug, no issues I've noticed. Not saying that settles anything for OP's specific outlet, just that it's not automatically a disaster in practice.

Appreciate both sides of this. For the neutral-fault scenario gravelfox88 is describing, is that something a regular multimeter check would catch, or does it need an electrician's tools to actually verify the connection is solid?

For what it's worth, the Tesla 10-30 adapter is a real listed product, not some third-party workaround, and the equivalent adapters other manufacturers sell for their mobile cordsets are built the same way. It's engineered expecting the derate to 24A that's already been mentioned here; the adapter itself won't pull more than that regardless of what the outlet is rated for. The grounding question upstream of the adapter is a completely different layer, and the adapter can't fix that part.

Anyone know if this matters for homeowners insurance? Not the electrician-safety angle, more whether an insurer could point to a non-code EV setup if there were an unrelated electrical fire claim somewhere else in the house.

To put some numbers on what's already been said here: NEC 210.19(A)(1)(a) and 210.20(A) both apply the 125% continuous-load rule, which is where the 80%-of-breaker-rating derate comes from. A 30A circuit tops out at 24A continuous whether the load is a dryer or an EV, and that part isn't really 10-30-specific. What is specific to the 10-30 is NEC 250.140, which used to permit the neutral-ground bond at dryer and range receptacles on existing installations but hasn't allowed it on new installations since the 1996 NEC cycle. That's the actual dividing line between a 10-30 and its replacement, the 14-30. A 14-30 looks similar, still 240V/30A, still a dryer outlet, but adds a 4th, dedicated ground conductor, so there's no bonded-neutral question at all. There's also a cheaper option worth knowing about: since EV charging doesn't use a neutral at all, some people convert the same wiring to a 6-30 or 6-20 instead, two hots plus a real ground, no extra conductor to pull. If you're using an existing 10-30 occasionally, the adapter is a known, listed way to do it derated. If it's a daily setup for years, either the 14-30 or the 6-30/6-20 conversion removes the grounding question instead of just living with it, and both are usually smaller jobs than a full new EV circuit since the wire gauge and breaker are already sized right. Worth getting quotes on your options before deciding.

Had almost this exact situation in my last house, a 1970s build with an old 10-30 in the garage nobody used. Had an electrician swap it for a 14-30 instead of running all new wire, since like Marcus Chen said the existing wire and breaker were already the right size for it. He ran an actual ground conductor to the box too, not just a new receptacle face. Total was a little under $400 including the new breaker, done in about two hours. Cheaper than I was expecting going in, and it meant I never had to think about the adapter question again.

Kind of a dumb question but how do you actually tell a 10-30 from a 14-30 just by looking at it? Every picture I search up online looks about the same to me.

Not a dumb question, they get mixed up constantly. Count the openings: a 10-30 has 3 total, two angled slots plus one round one, while a 14-30 has 4, an extra separate slot for the dedicated ground. If you're only seeing 3 openings on the outlet, it's the older 10-30.