I read this is not good. I have left over 5w that I'd like to use up. I wanted to mix it with the same Nulon but 10w but read it's bad for the engine. I couldn't work out why though?
When I have discussed very similar questions with oil techs in the past the answers they would give you, if they did reccomend against your proposal would be absolutely weak as water.
I asked them about a similar issue with trans fluid, doing a pan off service and fill with new fluid. The answer they gave was oh well that should be fine but we don't know what state the other left over fluid in the trans is, so we can't garantee the new fluids properties because it will be a mix of new and old blah blah blah ass covering load of crap. So you need to take it to a transmission shop and get the trans flushed and filled with new fluid to be safe and sure. Like what the heck I'm just servicing a 4 speed not building a formula 1 car.
So they would tell you, well we don't know exactly what mix you'll get so it might become a 7W38 or whatever and we haven't tested that grade so I'm not authorized to say...
They hate me cos I don't let them get away with taking the easy way out and half answering questions.
