Apart from the fact that your dog must never be left alone in the car in the sun (and not even in the shade), not even for a few minutes, here are some suggestions on how to avoid, or what to do if it happens, his getting sunstroke due to high temperatures.
Unlike us, dogs don't sweat, but cool down by breathing with their mouth open.
The first symptoms are breathing more quickly and if he slavers a lot.
You must do something at once. Should his body reach a temperature of 40-43°C he will go into a coma and could die very soon.
In which breeds of dogs is there a higher risk of this happening? Those with a short nose, like bulldogs, boxers and Pekinese, or those with long hair like Newfoundland dogs, Saint Bernards and collies. Needless to say dogs with cardiac and respiratory problems, as well as very old dogs, run a higher risk.
Here are some very important things you mustn't do if you want to avoid your dog getting sunstroke:
At the beach be sure it is a good idea to take him, and don't think keeping him under the sun umbrella will be enough. Wet his legs, head and belly. Make sure he drinks frequently.
Look upon you dog at the beach like having a small child. Would you take him there at noon?
Should it happen that your dog gets sunstroke, try to bring his temperature down and take him immediately to the vet. Here's what to do:
Once the danger has passed take him to the vet.
Advice and photos on behalf of Enpa Island of Elba