I'd say it is ok. The spec says it should be 3.8 - 4.5 mm, but I think the concern is that when it is getting worn-out it will stick-out more than the 4.5 mm and not putting proper tension on the belt. Although sounds weird that it is only sticking-out 3 mm. Is the tensioner brand new? FYI, here is a link to a good procedure for the belt change:i installed new timing belt , water pump, pulleys and tensioner. it is measuring 3mm. is that ok?