I'm traveling from Guatemala to the US in March, my passport expires on August and my Visa is on that passport. I know Guatemalan citizens are not required to have the six month validity rule but I'm afraid the airline staff will not know this and won't let me board. So, should I renew my passport and take both the new and old one? Will it be a problem if the old passport is still a few months from expiring?
If you are concerned that there might be an issue you should renew your passport early. When your new passport is issued, your old one is usually made invalid. Even if it's not for some reason it's still OK to travel with multiple passports, as long as they are yours.
So, should I renew my passport and take both the new and old one?
I'm from Argentina. When your passport expires authorities give you a new one and they do not retain the old one in any case. I always carry both passports with me, just in case I am required to show the old one.
If you happen to have a US valid visa on your old passport, present both documents.
Will it be a problem if the old passport is still a few months from expiring?
No. Never heard that you need to wait until passport expires to issue a new one. It would be totally inconvenient.