Road trip from Sydney to the north in 3 weeks in July. Where can I go?

Welcome to the forum.

For fairly good weather for camping - not exactly warm overnight, but not freezing - you need to get as north as Byron Bay. That will take you two days of easy driving. From there you can enjoy SE Queensland, including the Gold Coast, Sunshine Coast, and as far as Hervey Bay, perhaps for a trip to Fraser Island.

Beaches in SE Queensland can be extremely pleasant in winter, but the ocean will not be exactly warm, although plenty of people do swim at that time, on nice days.

If you pushed hard you could go as far as Airlie Beach, and enjoy sailing the Whitsundays, plus a trip out to the Barrier Reef - however with 19 days round-trip, you will be rushing through very good destinations on the trip both up and back.

It is over 2,000 km each way to Airlie Beach (without any diversions), which realistically means 4-5 nights each way. With just 19 days I would probably go no further than Hervey Bay / Bundaberg.

Become familiar with Google Maps, using the Directions function.

I agree with #1, it’s a long long way to drive to Airlie Beach and back and there is plenty to do along the NSW and southern Queensland coasts.

Where do you think it would be possible to camp without freezing?

What’s freezing for some is nice for others!

For climate data using google choose a town and type in “climate town name” and select the bom.gov.au site (they are the government meteorology site), For example I’ve chosen a town on the NSW north coast of Grafton –

http://www.bom.gov.au/climate/averages/tables/cw_058024.shtml

Then you can check the average daily max and min temperatures.

So when I travel overseas I use my home town average monthly min and max temperatures as a reference point.

For a Great Barrier Reef experience you could try something on the southern end of the GBR like Lady Elliot Island – not cheap but maybe a bit of a splurge event!

http://www.ladyelliot-island.com/

I can second Lady Elliot Island - not cheap but a good experience if the weather gods are kind to you.

It really depends on what your priority is and if it is Airlie Beach, you could head that far first, http://www.travelmate.com.au/map/ will show you the quickest route which is going inland - 1900 km. and 20.5 hours driving, something you could do easily enough in three days, even two if you had to.

The inland route does take you via some very different terrain to what you see along the coast or even closer to the coast, it being very flat country along most of the Newell highway north of Narrabri, a bit on the boring side but at least you can say you have seen a part of Australia many people do not even envisage.
If you settle on three days, I'd probably vary the route a little for something softer on the eyes and head up the New England Highway, the Royal Hotel at Tenterfield (~660 km. from Sydney ) great value at ~ $40/n, last time there for a single and it will be quite cold overnight going either inland route.

Anyway, three days to get there and however many days you want there ( you do realise they had a cyclone in March ), maybe 4 days would be enough and then you have 12 days in which to plan your return which is reasonable enough to pick a few spots to stay a day and a couple of nights with travelling on alternate days.

That's all fine in theory, but it is a really featureless drive up the inland route ... and cold as well.

It's up to you - if Airlie Beach is an absolute priority, it would probably be a lot cheaper to fly and leave that car at home, and use it for some days in a wide arc around Sydney.

You do not say Nicof whether you are hiring a car or have your own for with the former there will be restrictions on where you can go, usually hired normal 2wd vehicles being restricted to sealed roads and with quite a few national parks there can be unsealed roads involved.

For instance, if you chose to head north via shortest route to the New England Hwy. and on to Tenterfield, directions will be along Bucketts and Thunderbolts Ways, that being some truly spectacular countryside, far better than what you see going up the more southern part of the Pacific Highway.

From Tenterfield, if you continue on the New England Hwy. past Toowoomba and on to Monto via the Burnett Hwy., that is a distance of 600 km., there being lots of interesting towns for breaks along the way. About 30 km. north of Monto there is the picturesque Cania Gorge which has a a great small camping ground ( and also cabins ) or if still on the chilly side there is also a good value Grand Hotel in Monto.

https://www.npsr.qld.gov.au/parks/pdf/boyne-valley-parks-map.pdf shows the many NPs in the region between Monto and Gladstone but some do not have sealed road access, that applying to many NPs so if you have a hire car, it will be best to choose your route and NPs with any restrictions that apply.
Monto to Airlie Beach is about 760 km. going inland and it'll be about the same cutting back inland to Rockhampton so doing some overland exploring will mean some extra driving but not a huge amount and you will see some great countryside.

I suggest you just stick to the Pacific Highway / Bruce Highway along the coast (more or less) - whether it is a private car or a rental.

The inland routes have some occasional nice sites, but most of it is through fairly uninspiring Australian bushland. The coast road has access to some truly iconic places, for much of the way (except for the last 750 km to Airlie Beach - which is mostly canefields or scrub).

A great advantage in travelling up and back by different routes is that not only can you see different parts of the country but if you stick to the Pacific and Bruce Highways for both ways you will encounter very heavy traffic conditions in quite a few places, between the Gold Coast and Sunshine Coast in particular because of commuting people do into Brisbane and ten you also have a few regional centres in both states as well as major roadworks in northern NSW that you will need to contend with.

Going that route just once when you are taking your time on a return is more than enough and there are many beautiful areas of landscape you will find along the New England route, driving with far less to minimal and sometimes near zero traffic is far more relaxing.

If you returned from Airlie Beach along the coast, there are a number of places that might be of interest, quite a few National Parks including Cape Hillsborough, perhaps have a day trip or overnight at Great Keppel Island ( there being secure parking close to where the ferry departs and transport to terminal included ), Rockhampton has a Botanical Gardens with small wildlife section that includes freshwater crocodiles and further south 1770 allows you to do a trip to Lady Musgrave Island ( small island and lagoon on southern end of the GBR ) , Google Fraser Island Tours to see a huge range on offer and from Hervey Bay you can do whale watching tours.
From Sunshine Coast to the Gold Coast is heavily developed and you will need to use caravan parks for camping in that region and likewise for Byron Bay.
Travelling south of Byron Bay, there are a number of National Parks that you could consider camping in as you make your way back to Sydney.

Thanks to everyone for replying!

I've decided to travel to Noosa instead of airlie Beach, because of the distance.

So, you think it's possible to camp for free in my trip? I have found some national parks in Google.