1991 liberty engine oil

[nala]

Is it true that if the wrong engine oil is used that it will cause the
engine to run irratically?

 

[Vema]

false:
oil that is fuel fouled will, so engine wear and how it is used ie short
trips long trip etc determines how soon the oil will deteriorate

 

[nala]

I have now discovered that it is true. I was using oil that was too
heavy-20w-50. Having changed to 10w-30 the problem has gone.