Sometimes either is a must do thing but... The smallest amount is all that should ever be used. I have tried to start two idi motors with either. One motor had so much either being sprayed directly into the turbo intake it was wet and dripping... No fire and no smoke... It was almost like the intake was plugged up and not sucking air... The turbo was spinning...
The other motor almost the same thing.... Turbo and no smoke and no fire.... Both motors didn't have a working glow plug system.... I still have no idea why those motors wouldn't fire.... About a glow system that wont work... The best place to check it is the main engine wireing harness plug. The two yellow wires on the end of it usually get corrosion on them. The it heats up the plastic plug... then it melts. A good place for an electrical fire under the hood. After a start check this plug... See if it feels hot or you see some melted plastic... then replace the feed wire to the glow plug controller.... After its wired directly you will never have a power issue at the controller again. I did this and several others with great results. Large speaker wire seems to work great... It has plenty of current carrying wires in it... Solder on the heavy lugs and its done....
