[Mark_T]

From what I understand, if your AOS is bad then it will be difficult to remove the oil cap due to excessive suction. I don't know if hot/cold makes a difference, but I would venture to guess that if your AOS is bad and you have thick smoke billowing out the pipe, it might not be a good idea to keep it running long enough to warm up. I also don't know what amount of suction, if any, would be considered normal, but perhaps someone else can answer that.