I'm working on taking off my exhaust manifolds and replacing them with headers. The only problem is I'm havin trouble gettin the old bolts loose. I've been spraying them with penetrating fluid everyday for a week before I even attemped to turn em loose. I'm also worried about breaking the bolts and reallly digging myself a hole. Any tips or ideas?
If your truck is higher mileage and has never had the manifolds off, I suggest leaving it alone. You don't want broken bolts in the heads. Its a 50/50 chance you will break one or more off in the head. In my opinion its not worth it. They only way I would consider headers is if they were going on a fresh motor or the heads were already off to be reworked.
Use an air chisel and put force directly on the head of the bolt as if you were trying to push it into the cylinder head. Make sure you use a blunt tool when doing this. I got 13 out with my fingers this way two snapped and the other took some heat. Using a right angle drill you can drill and tap the bolts easily do all the work from the wheel well with the plastic liner removed.
Also, pb blaster is the best penetrating oil out there! I agree with leaving them alone if they are not cracked or broken. But with the plastic wheel wells out and you can get an impact on there then that's easily the best option. Hopefully you don't have real rusty motor because if you do then those bolts are more than likely soft and thin And you will break them.
Use the "Freeze-Off" nut&bolt loosening agent. I have had luck heating the bolts up and then spraying some of the "freeze-off" on them to help expand and contrct them, breaking them free. As White Max said about AeroKroil, try that as well!! It's expensive, but it does work. Keep sparying them and then drive for awhile. Let it cool down and spray them again. This heat and cool cycle along with some penetrating lubricant will be your friend in safely removing the bolts.
I had 107000 on mine when I did the headers. I drove the truck for a while, and while it still hot, I put pressure on them to TIGHTEN them and then loosen them. No need for any PB blaster, they all came out easy, except the last one. I knew would break anyway due to corrosion.