Originally Posted by Brian Carlton

It all depends on the condition of the engine. Since the SD got the rebuilt head, the light is an accurate indicator of how long the engine needs glow to start. Even at very cold temperatures, it will fire right off at the end of the light. Sometimes, I'll play it safe and wait an extra ten seconds, but I don't honestly believe the engine needs it.

This engine has never failed to start in about one second, after the new head was installed, independent of ambient temperature.

It was, by far, the best investment I have ever made in the vehicle.