Just realised when doing a small top up to the oil in my 02 1.6V Focus this morning, about 200ml at the most, I'd put in the 15W/40 oil that was in the garage not the 5W30 that's in there – will this damage the engine at all?
Yep, you'll be fine until the next oil change. Even if you'd filled the whole thing up with 15w/40, you wouldn't self-destruct it. I had an old van that ran better on 20w/50 than the 5w/30 that was recommended for it. I did swap out for a thinner oil in the winter though.
I have cause I just have and I live in Arkansas where where most of the time its 80+.
Right now its only dropping to around 25 at night.
I guess I could put in some thinner on the first as I need to replace my oil pan. Just wasn't looking forward to changing my oil just yet but I need to do the pan so yeahh.