I have a buddy with a stock 1989 w250, 5 speed, with straight pipe. His truck makes a slight knocking noise while at cruise speed. Its not overly loud, and doesnt really change tone like a bearing. And no smoke such as a bad injector. i told him not to worry about it, 330k

Should he ?

 

It is very hard to give meaningful advice on a guestion such as your's without knowing a few things first. Does your friend run fuel additives? You say he is running straight pipe. That could mean the knock is really quite loud. A slightly weak injector may not smoke. Some knocks and noises do not necessarily cost money but then again it might just as well be looked into. It is the old pay me now, or pay me later. Has he kept a close watch on his mileage? Is he losing water? Is the engine harder to start? Is there oil in his radiator? I guess you get the meaning of all the questions. I myself, need a little more to go on to answer your guestion. Try and do a little trouble shooting without causing any great alarm. It may be just a tired old engine or a minor tune up.

 

Mine was knocking, a little louder than what your talking about, and it was a blown head gasket, though I do have a lot of performance mods.