The new to me 1985 k5 is smoking after start up. It runs and smokes. Any thoughts? It cntinues after start up, it is burning oil. My mechanic wants to replace the motor, it's the orginal 1985 motor. It was supposet o have been rebuilt 4 years ago, but what can you believe from a seller. I can't afford a crate motor so we will probaly go with a rebuilt or a used motor.