Toyota Repair: 1998 Toyota Sienna (XLE) Engine Oil Sludge, engine oil sludge, sludge problem

Question
My Sienna was manufactured 5/98. I bought it NEW. It currently has 21,163 miles on it and our local Toyota Dealer performs all of the maintenance. We use the van for plesure and vacations only so it stays in the garage alot. I have the oil changed at 3,000 miles or less. but most of the time I have the dealer change the oil due to time (six to eight months) because we don't dirve 3,000 miles in that time. Does or can oil go bad in that time? That is to say is six to eight months between oil changes to long if we only dirve the van to dinner on weekends? I don't think that I have a sludge problem now. However, how would I know, or find out? Based on our driving history do you think I will encounter this problem? At what mileage does this problem usually show up? My over all concern is that I will exceed the 8 years (2006) were Toyota will cover the repairs before I encounter any problems. Do you have any recommendations like don't wait 6 to 8 months between oil changes?

Thanks for your answers and any advise!

Harry  

Answer
Hello Harry, welcome to my expert page.
Mileage is the only thing that matters as far as oil changes are concerned, time has no effect on oil, you can leave it in the garage for a year or so without changing the oil, the oil will be in the same condition, the operation of the engine causes the oil to break down and possibly turn into sludge in extreme cases, as long as you change the oil every 3-4000 miles you will have no problem.