I know there has been a lot of talk about how oil color does not indicate the need for changing the oil, but one thing I noticed on my GM 3.4L this interval is that the oil turns dark in color and also seems to get thicker. By thicker I mean when I check the oil on the dipstick I can distinctly see a difference from the thickness of the oil when new (I guess viscosity may be a better word than thickness). Now I’m talking about my 2002 Grand Am GT with about 32000miles total and 2200 miles on this oil (it’s the 10W30 Valvoline dino oil put in by a garage). The car has been driven about 99% highway with very little stop and go (I’d say less than 5% of those miles). The car is also driven fairly easy (very little hard acceleration). I noticed that the oil looked new for about the first 1000 miles or so and definitely looked darker by about 1500 miles. When I checked the oil yesterday, it was pretty dark and noticeably thicker. The oil history on this car is dino oil (usually 5W30, sometimes 10W30) at approximately 3000 miles (it has gone up to 5000 miles once or twice in the past). Now I know I shouldn’t be going off the color of the oil to decide when to change it, but when I notice it’s thicker than new oil, I start to wonder if I should change it. I know that an UOA may not show high wear or anything, but I’m sure it would show a viscosity change from a VOA of the same oil (at least at cold temperatures). Also I'm planning on switching to a synthetic oil next oil change (in a month or two). Is this "problem" with the oil thickening better or worse for synthetic oils?