Why is my dog drooling?

I have a pitbull puppy. Almost a year old. He weighs about 58 pounds. He only drools mostly when he is outside but I've seem him drooling inside a few times. This happens when I'm taking him outside to the bathroom or when he goes on a ride with me in the car. Sometimes the top of his head like pulses I guess you could say. I'm pretty sure that he's healthy as he's been to the vet quite a bit and the only thing wrong with him is that he has dry skin. He ate a box of rat poison a few weeks ago but we got everything taken care of and he had an allergic reaction to the Vitamin K shot the vet gave him but he had been slobbering before all of that. Any ideas on what it might be? I'm sure if the vet saw something he would have said so in the many times we have been. We plan on getting him fixed here pretty soon. Thanks all in advance.

pits do normally drool over excitement or waiting for food it is normal for them to do this. I love this poem and since you have a pit thought you would also.

what dog do i speak of?????????????/

Their love is like no other; their heart is pure as gold.

Yet while going on a friendly walk, they're faced with stares of cold.

They're so very close to human, in how they act and what they do.

Unless you've known their devoted love, it's impossible to explain to you.

They are greatly more misunderstood, than any other breed.