I read somewhere that you could use stimpaks on Dogmeat but I don't know how.Anybody?

VATS him, to check his health. Then talk to him. There should be an option, but only if he's hurt, to give him a stimpack or two to get him healed.

Right. You can administer a stimpack to him any time, even when both of you are in the thick of battle, simply by talking to him. I think it restores his health completely.

I also herd that he heals himself after battles, not sure but I never use health on him and he ain't died yet

All companions will automatically heal after combat. Your companion could be nearly dead, and all you have to do is pick a fight with a rad roach, and afterward, your companion will be fully healed.

I got a message that his limb was crippled but when I talked to him I didn't get an option for a stimpak but I didn't get a chance until after the fight.I guess he healed himself by then.

Correct. All followers heal themselves after combat. However, it is ONLY after combat. If Dogmeat triggers a landmine with no enemies about, he will go into his next battle hurt.

Oddish-your signature made me giggle.

Thanks... I have a whole list of 100 or so weird and wacky activities, but it's in a topic that's slipped into dead post oblivion. But another good one was about Dogmeat:

#88 - Give Dogmeat a less derogatory name. How would you like to be called "Strange Meat Pie"?

Sometimes a stimpack or two is the difference between life and death for your four-footed companion. Or to put it another way, between having Dogmeat and a piece of dog meat.