I'm a Service Training Instructor for Ford. My prime areas of instruction are drivability classes on both gas and diesel engines. I own and drive a 1999 Power Stroke plus I teach and drive the latest stuff for the company, such as the New 6.0L. I've been running a synthetic oil since 17k and Amsoil Series 3000 5W-30 since 38k. I currently have over 85k on the truck. If the gentleman with the '99 would look on page 36 of his Power Stroke owners guide, he will find Ford's specification for engine oil. The first one is "WSS-M2C171-C". That is listed also on the back of the Amsoil bottle that I have in front of me. The other specification is API CG-4/SH, the bottle currently has CH-4/SL, which is newer and better. I don't know what it takes to get the authorization to stamp WSS-M2C171-C on the bottle, but I'm quite sure it didn't come cheap or easy. With that on there, you have Ford's blessing to use Amsoil Series 3000 in your Power Stroke. If someone in a dealership questions you, show them your owners guide and the bottle. I'm almost certain that they'll change there tune. If not, ask to see a regional rep. A little about the API rating. There are a lot of oils out there with just an S* rating, or an C*/S* rating, but very few with an C*-4/S* rating. This engine does require a lot of Anti Foam additives, because of the fuel injection system, and the -4 is your clue that oil has plenty of them.

2nd topic, The oil pan is the same size on all Power Strokes from 94 to 03, on 250's-550's, which is a 15 qt pan. The old IDI 7.3l was a 10 qt pan. Marketing strategy in the early years, to bring it more in line with the old engine costs, was 12 qts. (When they went to 14 or 15 qts, all they did was change the dipstick.)That strategy failed, partly because you were 3 qts low on additive package and partly because the silicone used in the oil pan gasket would leach the anti-foaming additives out of the oil until about the 25k mark. Ford has a test in their PCED called an oil aeration test, that checks for the depletion of the additives. Our 94 training vehicle would be depleted in about 2k. My 99 was still good at 5k on Motorcraft oil. I've currently have 14k on the Amsoil and it still passes that test with flying colors. I'm running the Motorcraft FL1995 oil filter (which is a 3 micron filter) and an Amsoil by-pass filter, which brings my system up to 17 qts, plus the 3 in the high pressure oil system, that you mentioned, you can't get out. At least, not without a lot of work. I've been changing the oil and sending in oil samples about every 10k. This is the first time that I didn't change at 10k. My oil samples have been looking great and I looked under the valve cover with a bore scope last fall, to see if I was building sludge with my new oil change intervals. I was a little reluctant, because I've had several Ford gasoline engines over the years with over 200,000 miles on them without ever removing head or pan, all with 4k oil and filter changes. The last one I signed the title over at 230k and the engine only used a qt every 2k, when I got rid of it. This 99 represents my first diesel and my first use of synthetics.

3rd topic, oil thickening; I did my first oil sample at 17k with 5k on the Motorcraft 10W30 in the crankcase. It had thickened to about mid-range of a 40 weight oil. What has really impressed me about the Amsoil Series 3000 5W30, is that every time I've had it checked, with 10k on the oil, it was still mid range for a 30 weight. That’s partly what drove my decision to just change the 2 filters, add oil and try another 10k. Old habits die hard, so I'll probably change the oil anyway this time around.

4th topic, oil change intervals; I can't advise you to go beyond the guide lines spelled out in your owners guide, due to warranty, but I have noticed a few interesting things by looking around. Remember, mine currently requires 17 qts with the by-pass filter. If you go to Navistar's website, you'll find that their version holds 18 qts and has a recommended 10k oil change interval. The Power Stroke in the F650/750 series holds 20 qts and has a 10k oil change interval.