Posted by chriscase on Saturday, July 09, 2005 at 3:10PM :
In Reply to: 318 with a cracked head? posted by Jim on Saturday, July 09, 2005 at 2:13PM :
If it's not using water mysteriously (no leaks) then it is probably not a cracked head or blown gasket. Running rough could be tons of things: burned valve, bad plug, bad plug wire, bad carb, bad cap, bad rotor, bad brain, bad karma, bad hose, bad hose job, bad gas,bad burrito......
Check the cranking rhythm by grounding the distributor wire so it won't start. Then crank. If it has bad compression, it will have a definite rhythm- ni-nit-nit-nit-nit-yump-nit-nit nit. The yump could be the dead hole, only 10# shy on a compression test. Otherwise, a bad head or gasket can let in enough water to make it run rough, yet still test OK on compression. Usually a bad head/gasket will make it over heat. If no overheating, it may last a long time, no way to tell. Hoe expendable is the engine? The longer you run it, the more damage done internally.
At the tune up shop, we used to test heads/ headgaskets with the smog machine sniffer. There shouldn't be any hydrocarbons in the radiator.