Electric fan comes on when hotwired, comes on with a/c, but not when engine gets hot, what part controls this? Of note, temp OK for up to 20 miles then begins to climb fairly quickly. Several months ago I added some stopleak to radiator, turns out was a leaking small hose, could the stopleak cause the temperature climb, must I remove lower radiator hose when flushing system or would the drain outlet be sufficient? Manual fan turns by hand with mild resistance. Thank you in advance!