Guys i'm looking for some advice. I've a 2008 Fatboy with only 5,000 Km on the clock. Its been run in on the Harley 20W-50 and i've had one service which again the Harley 20W-50 was used. I personally feel that using a 20W-50 lubricant in the Irish / British climate is not a good idea as its to heavy an oil and takes to long to get to a temperature that enables the oil to circulate properly at start up. I was looking to switch to Mobil Racing 4T 15W-50 but mentioning this to a dealership sends them into overdrive. The are totally against the idea of a bike that has been "run in" on a mineral oil being switched to a synthetic oil. Personally i can't understand this, this is certainly not the case for cars. They also claim that a 20W-50 engine oil perfect for our climate. Could anyone shed a bit of light on this ? Has anyone had any experience (good or bad) with changing oils ? Thanking you all in advance !