I don't know if my engine will last 500k miles, but we have 160k miles on ours and it is running great. On our gas motorhome, I needed a valve job after 70k miles, and I would have really started to worry about the engine if I had gotten anywhere close to 160k miles. Our transmission went totally out at about 80k miles. On our current coach, the engine and transmission is not even on my worry radar. Right after we bought our coach, I asked (out of curiosity) what the engine replacement coach was--Caterpillar quoted me $25,000 for a core exchange in 2001 for a 3176 (10-liter) engine.