link doesn't work.

btw; if an airfilter is closed, the motor will run richer and therefore run cooler. rich means less air (since it can't breath, it's getting less air) a clean filter means more air, so leaner, which means more heat. You don't tune an engine with an airfilter, but you do tune an engine with the airfilter on, so if it ran okay with a clean filter, it will run richer with a dirty filter if the same settings are used.

it might be running hot because he's always on the gas he never lets off.

i think that might be why

I know that this is an old topic, but did you figure it out? If not there has to be an airleak, or resistence in the driveline, one wat to find out is to put your motor and fuel system in your dads truck and see if it works or gets hot. If with a full swap it still does, then its in the drivetrain

I would think its something with the bearings or the o-rings.