Bringing a US-titled 1986 pickup back from Mexico after decades there: do EPA and DOT rules even apply since it started out American?

There are two separate questions here, and they resolve differently. Age is what exempts the vehicle from EPA and safety-standard compliance. That does not depend on where it has been registered since, only on how old it is. It does not exempt him from paperwork: the forms confirming the exemption still have to be filed. Duty is the separate question, and the exemption does not touch it: duty applies to value above the ordinary personal exemption of $800, the same as any other returning good.

The number that actually matters here is 25: once a vehicle clears that age, NHTSA treats it as exempt from the emissions and safety-standard rules that would otherwise block a newer import. Past that, this stops being a compliance problem and becomes a logistics one: he still has to make the declaration at the crossing itself, in person, with the paperwork in hand. Tell him to bring the original title, the export papers and the current Mexican registration together, rather than assuming the exemption alone gets the truck through.

I hadn't run into the 25-year exemption before this thread, so thank you both. That's useful outside this specific case too. The part I'm still not clear on: does the exemption apply automatically once the vehicle clears that age, or does he have to actively claim it on the declaration, the way you'd claim a preference under a trade agreement? I ask because 'exempt' and 'exempt if you remember to say so' are very different things to get wrong at the border.

To mark the contrast: we would not treat this as returned-goods relief at all: that relief exists for a defined window after export, and this vehicle has been away for decades, well outside any window our authorities would recognise. What he has found instead is closer to how we treat a genuinely old vehicle under separate rules of its own, not as something coming home. Worth knowing if he, or anyone reading this, deals with something away for far less time.

That's the answer I needed. Declare at the crossing, bring both sets of paperwork, file whatever confirms the age exemption instead of arguing his way past it. I'll tell him it really is this simple. Nothing here needed to be complicated.