Maybe once or twice, but from current personal experience, you can change nothing but oil in a 4.6 for over 140,000 miles, never look at the coolant or the tranny fluid or plugs or fuel system, and let it sit in a field for 18 months, then gas it up and get it running about 19 hours a day again, logging more than 75 miles each day in 4x4 low range, and STILL not check or change any fluids in it (besides the oil and filter), and it will perform like it did when it was new. I don't think the 4.7 or the 4.8 could do that, nor do I think the trannies behind them would hold up as well as my 4R70W has so far.