Removing a stuck steel bolt from an aluminium engine block requires patience and skill. Aluminium engine blocks can easily be rendered useless through reckless attempts to remove stuck bolts. A steel bolt gets stuck after some time because it has fused with the aluminium block through galvanic action. Although this happens slowly and at a very small scale, it is enough over a period of time to seize the bolt permanently. Remember that in performing the extraction procedure, you have to exercise a lot of patience so as not to induce further damage to the aluminium engine block.
Apply penetrating oil around the stuck bolt. You want the area soaked so use plenty of oil. Allow several hours for the oil to work itself into the threads of the bolt.
Fit the locking pliers very tightly around the remaining part of the bolt and apply counterclockwise pressure on the bolt to unscrew it. Sometimes, it helps to give the pliers a sharp rap with a hammer in the direction you want it to turn to jar the bolt loose.
Heat the steel bolt (with the propane torch), not the aluminium, until it starts to glow. While heating the bolt, tap on it to help break the fused area. Wait 15 minutes and then reattach the locking pliers again. Try turning the bolt again in a counterclockwise direction. In some cases, it helps to try to turn the bolt in a clockwise direction before applying a counterclockwise force. This procedure does not always work on the first try. Repeat this step up to 4 times to try to get the bolt out.
You will need to go to a machine shop if the procedure in step 3 does not work for you. There are other methods that can be tried but the skills and equipment required are beyond the realm of the average DIY person. Nitric acid reportedly works well in freeing steel bolts stuck in aluminium but the acid is not readily available as it is an industrial substance that requires special handling. Bolt extraction kits or easy-outs sometimes work but sometimes don't. The tapered structure of the extraction bit tends to force the remaining bolt outward, which ends up freezing the bolt in more. When you force it more, the extraction bolt can snap off, aggravating the condition.
Aluminium will belt before it starts to glow so be very careful when you use the torch. Heat the steel, not the aluminium.