I've come to notice that the oil runs great for the first 2500 miles, then it starts to eat it (not burn it, but it starts getting low). I'm guessing that the oil is breaking down? anyone else?

 

no its not breaking down. when oil breaks down it starts to get alittle bit of a burnt smell to it as the viscosity leaves it kinda like burnt tranny fluid that comes out of a cooked tranny, atleast thats what I've always heard. My car has been running mobil one for awhile and its always right where I fill it to after 1000 and 1500 miles. At 3000 its about a half quart below where I fill it to sometimes and sometimes its still right on the money. I believe it has to do with the pcv system and how many WOT blasts that there is. I may go through a couple oil changes and never see a change in the level and then be about a half to three quarters low on the next change and not lose any to speak of on the next couple afterwards. Its weird like that.

 

i have a catch can, so unless the oil is evaporating it couldnt get into the intake. I think i'm gonna pick up a breather too, just to see if that helps any. I'm still curious to see why the last 500ish miles the oil is lost quicker though.

 

Even synthetic oil has a volatile component that will evaporate over time. This accounts for practically all of the missing oil in most cars. My cars and trucks use about 1/2 to 1 quart every three or four thousand miles.

Some oil gets by the rings and is combusted. What's left behind becomes ash. Regular oil leaves a larger amount of ash, synthetic oil leaves less. Before the days of detergent additives and synthetics this ash and other products would stick to your engine parts rather than become suspended in your oil. That becomes sludge and varnish. The only way to get rid of it was to change your oil very regularly This is where the old "wisdom" of 3000 mile oil changes came from. It used to be mandatory or your engine wouldn't last very long at all.

Now, with modern additive packages, it becomes less important to change oil at 3000 miles or below. However, you just can't stop some people from changing even before 3000 miles. The soot and combustion by-products are suspended in your oil, to be trapped by your filter. Soot is pretty small and isn't trapped as well as other bits. That's why your oil looks black over time. You can have dark to black oil and yet still have a significant portion of the oil's additive package still available, making your oil look icky but still be quite functional. Modern fully synthetic oil can last over 8-10 miles with oil filter changes and top-off oil. Get enough filtration and it can last last farther. Then, time and the robustness of your additive package become the limiting factor.

Some LS1s are known to have oil consumption problems. Mine doesn't, so I haven't had to know a lot about it. Many do, though, and can be better explainers of it than I can.

 

I've been putting in a lot more WOT time since I added headers and a Predator tune.
Since then I've seen my oil level drop between changes. I find that I need to add 1/2 to 1 qt after about 2000-2500 miles with a lot of WOT time. I've been running Mobil 1 5W30 since I got the car in 2000. No smoke or hint of oil in the exhaust, so I don't think there's any blow-by.