We are flying into San Jose, and driving up to Arenal and then down to Manuel Antonio.
I would like to fit Tortuguero into the intinery, but wasn't sure if this was too far out of the way. We are visiting for 8 nights in April.

I would say that it would be to much for only 8 days, especially with Arenal and MA already scheduled. Tortuguero is in the upper Caribbean part of CR, and you can only get there by either boat or plane, which can take up to a day with travel. I personally would skip MA and go to Tortuguero, but that's just my opinion.

I agree with ewesthoff. Too much for 8 days. I have not been to Tortuguero yet (would definitely like to check it out sometime...), but did really enjoy MA on our first CR visit.

Arenal and MA fit nicely into an 8 day trip, and you'll get the contrast of volcano and beach. I'd stick with your original game plan and keep Tortuguero on the back burner for another time.

I'd stick with your original plan - it's an easy trip for a first-timer and will give you a lot to see and do; it's what we did for our first trip. Adding Tortuguero would be too much for 8 days.

Arenal and Manuel Antonio will take care of 8 days. I'd save Tortuguero for another time when the turtles are nesting--Tortug. is a great area, lots of wildlife to see, but the turtles are a big draw--truly amazing. July-October. . .

Keep in mind you may need to stay first and/or last nights near the airport depending on arrival/departure times. . .

Have fun!