my experiance/understanding of the "the relatively high temperatures involved with fork lift engines they have a tendency to seize into aluminum cylinder heads" is not actually "high temp" (and really forklifts and cars all run at the temp the cooling system is designed for) as much as it is that on some engines, the last bit of threads on the spark plug extend into the compression chamber, and after some time, they have a tendency to build up the same hard carbon depostis as the rest of the compression chamber. This is not a problem with the K21 and k25 engines as their last few threads do not extend into the compression chamber, but was a problem with the 4g series Mitsubishi motors. a coat of nev-r-seize (anti seize compound) on the spark plug threads before installing them makes a huge difference when removing them later, but this is -not- recommended for the k21-k25 engines as it can effect actual heat level of the spark plug, creating a cooler spot in the combustion chamber.