Skip this post if you don't want to read all the ins and outs of crossing the Chile-Argentina border via Los Libertadores. I found it helpful to read about other travellers' experiences, so this is in the hope that someone doing a similar trip will be helped by the info.
The Los Libertadores pass winds up the mountain in a zig zag, with 29 hairpin turns up to the top. It's a well-maintained road though, and big lorries were easily clearing the turns.
Crossing the border was quite a convoluted process. The Chilean and Argentinian border guards are located at the same place, so you're allowed of out Chile and in to Argentina at the same time. Still, getting across the frontier involved jumping through several hoops.
1. At the first post, we had to show the dude our insurance document and passports. He asked how many passengers were in the van and gave us two copies of the same form requesting information about the vehicle and owner (I'll call this Form A) and a long strip of paper with space for lots of stamps (I'll call this the Stamp Sheet) -- it was to be stamped by everyone we saw so that the last person could check that we'd jumped through all the hoops.
We filled in both copies of Form A (Word Lens came in handy!) - think you're supposed to fill them in with identical info cos they keep one and give you the other. We filled in one each but no one seemed to care. We then drove on for quite a while until we hit the actual border crossing - if Mario hadn't been with us, we'd have driven right past it -- it's possible to do that so trucks with prior clearance can just go straight through. There's a sign in Spanish telling cars and buses to turn left in to the border crossing. Our van only just fitted under - we're 2.9m and the hut you drive through is 3.05m. Suppose if we'd been taller, we'd have followed the buses.
2. The first booth at the border crossing is for human immigration. We had to fill in the usual immigration form and also give them 2 x Form A, the Stamp Sheet, our passports and our Chilean landing cards. They kept the Chilean landing card, stamped the immigration forms, 2 x Form A, the Stamp Sheet and our passports and gave them back to us.
3. Next we rolled along to the vehicle immigration section. Here we had to present 2 x Form A, the Stamp Sheet, the vehicle owner's passport and Chilean tax number (RUT), the vehicle registration document and the document written by the notary saying Salvatore gave us permission to take the van out of the country. First the vehicle was allowed out of Chile - the Chilean rep checked everything was in order. She put my passport, RUT and vehicle registration document aside quite early on. She stamped and signed the notary document and kept it, then she stamped both copies of Form A and the Stamp Sheet and passed them to the Argentinian rep. The Argentinian rep then had to look something up on the computer but there was some problem with some sort of code which meant we had to wait ages, but eventually she stamped both copies of Form A and the Stamp Sheet, gave us one copy of Form A and the Stamp Sheet back and we were on our way. Oh yeah, while I'd been sorting that, Paul had allowed a dude in to the van to check for things like fruit, veg, meat and other products that aren't allowed across the border.
Then we were off. We didn't actually cross the border until some way away. The frontier is inside a tunnel and marked by little Chilean flags and Argentinian flags on the wall. Not very obvious and easy to miss.
4. Some way after that, there was police post where we had to give the officer the Stamp Sheet. And that was it - first border crossing of the trip done!