Driving from Antigua Guatemala to Guanacaste, Costa Rica

There are no freeways, it is mainly two lanes roads, cargo traffic on the main Pan Am Hwy or CA-1.

Just plan on border crossings taking time, as you ext one country and enter another...

You might be better served to read the website "Driving the Americas", since its is for people driving personal vehicles across the various borders in Central America and South America.

As long as you have the Original Title, in your name, same as your Passport, you should be fine. What plates are on it?

Do you plan on stopping along the way anywhere to see cultural, natural and interesting areas? if not, then there would be no dirt roads to encounter. From motorcycle blogs, the hardest or most frustrating border to cross is out of Nicaragua and into Costa Rica. Took a recent traveler 6 hours to cross....so plan accordingly (mornings) and don't drive at night...

99% of travelers to the region use the public transport, not a personal car.

There are no freeways, it is mainly two lanes roads, cargo traffic on the main Pan Am Hwy or CA-1.

Not true, there are sections with 4 lane divided highway, example is road from Antigua to Guatemala City, also in El Salvador.

Thats about 1000km if you go via El Salvador or 1300km via Honduras and the Pan American highway and its pretty straightforward either way. You'll only find dirt roads if you decide to detour off the highway and the main routes are in very good condition. If you live in Guatemala aren't you required to apply for a Guat driver's license after 6 months? Comprehensive insurance cover normally covers you for other CA countries, local liability cover does not. Cars on CA plates require special papers to cross borders- you need to apply for these at the National Registry detailing your journey and you'll be given a certificate to present at each border crossing. The pain is you have to stick to the dates you detail on the application. Watch speed limits vary carefully- nevertheless you will probably get stopped at some stage by cops looking for bribes. Smile, be polite, never argue, use your feminine charms but don't pay the bribes just say you don't have any cash. Take the ticket- the reality is they won't even issue it. If they talk nonsense about seizing your passport, plates or license say you will follow them to a police station to sort it out. They'll soon get bored and you'll be on your way. At borders use the "helpers" (kids) who for a few dollars tip will run your papers around the various offices. Take lots of copies of your passports and vehicle docs and keep an eye on your stuff. Have fun!

Thanks for all the info! I will take a look at that web site :)

The car has Guatemalan plates.

Thank you for all the info! You might be right about technically having to apply for a Guatemalan driver's license but I don't think that anybody does that in practice, and when I last looked into it it wasn't even an option without me getting residency here (I go in and out of the country on tourist visas, and I know people who have been here for decades do the same).

Your comment "Cars on CA plates require special papers to cross borders" struck me. I haven't heard this advice from anybody else! Where is the National Registry? What sort of papers would I need? Do the papers have a name?? Thank you for your help with this!!!

Its just that you said you "lived" there- its the vaguaries of actually being a permanent tourist that confuses the issue. Eventually having ownership of a Guat. registered car but driving on a UK license could cause you problems, who knows?
I'm sure you realize that these are major drug running routes plus they do not want to allow the free movement of stolen vehicles across borders. To prevent this cars on CA plates need prior permission to cross borders, foreign plated cars can cross with the title document in the drivers name. You can google the Registry. You need exit papers for the car- you buy the forms and stamps and fill it in with the dates you will be crossing the borders and present this together with your car documents, title, passport etc plus copies. They will issue a certificate that you will need to present at borders.
You say you "haven't heard this advice from anybody else" but if you know people locally who do this then why are you asking here?...I guess they'd be the best people to help you. I've only been driving around CA for a decade or so...some people certainly come and go freely with bribes and know-how (particularly those who have frequent business across borders who are well known) but I wouldn't recommend it to you for any number of reasons...

Why are you driving to Guanacaste? It is far less hassle, and much easier, to just take a bus...epsecially if you don't plan on seeing anything other than driving thru each country to the next border, as crossing with a vehicle, takes 3-5 times longer...

Thanks for the suggestion. We did consider the bus and plane as options. Taking a car is better for us due to the number of people, amount of luggage, flexibility and the various places we would like to be able to visit along the way.

Some interesting videos on YouTube. Maybe not the answers you are looking for but educational none the less.
https://www.youtube.com/watch?v=8S33VZfu2OA for example.