Optimum Sell/Trade Time

[Lubehead]

I've got a 2010 X535d. I love it and it's my work vehicle. It's my second E70, the first being a 3.0. I put an average of 25k annually on the truck, and it has about 56k as of today.

I'd like to hear opinions and input on what may be the optimum time to sell this truck and get into a new one. I know the diesel is good for a lot of miles and that ultimately it's the roll of the dice as to what maintenance costs I wil incur over the next, say, 50 to 100k miles. From a financial perspective what is the best case scenario? I know this has several answers and one is not necessarily superior to the other, but I think it may be an interesting discussion; i.e. should I always turn them over every 2 years and never be without a warranty or perhaps keep it till 75 or 100k or beyond expecting the residual value to still be significant enough to repeat and start again.

I have a very successful business associate who operates an aggregate company. He buys crushers, and sells them after 3 years. The first two years are warranted and the 3rd year they are not. He has an excellent reputation such that the seller of the new crusher gives him top dollar for the used which has a ready market. His philospohy is that every day down he loses about $15k so he operates on the basis of the least amount of downtime as he generally incurs no repair cost for the crushers he operates. This is a good analogy to what I am looking to do, just looking to fine tune the best point to obtain the lowest operating cost given my vehicle of choice.