Steve,
I have been buying my 0/20 Mobil 1 at Walmart in one quart bottles for several years now. I use 3 1/2 quarts per change so I buy 7 quarts at a time.

Mobil 1 is my preference. I don't know if there are better oils than Mobil 1, but if there are, I don't really care because I get good results with what I have been using for years.

I change my oil religiously every 25,000 miles, whether it needs it or not.

Dan

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Mobil-1 Extended Performance (now with a Tan Gold colored Lid and only about $3 more expensive in the 5 Qt jug then the standard Mobil-1) is also guaranteed for 15,000 miles. I have 9000 miles on my current oil change and it looks like brand new oil. Castrol Edge (Gold Bottle) also is guranteed for 15,000 miles. For now the filter for the 2010 Prius might be dealer only I believe I read it takes a cartridge filter.

Special note I would follow the 5000 mile intervals while in your powertrain warranty.

Do any of you with the long drain intervals do oil analysis. 25,000 miles seems a bit long, even for Mobil 1. Amsoil maybe, but not Mobil 1.

krousdb plans to analyze the current oil, and I am advocating the TBN test because that is more of a concern in my mind) than shearing out of the viscosity range.

I will be sending a sample in in a few weeks after my next change. Why would you say it's OK for Amsoil and not for Mobil 1?

Mobil 1 may not be a true blue group IV synthetic. Amsoil is, but I don't think they get their group IV oils AMA certified.

I currently run the regular Mobil 1 5W-30 with a puralator no slip grip oil filter. I was thinking of switching over to the gold cap for the 15k interval between changes. Will that oil filter I'm using last 15k, and if so, can I maybe get 20k out of both the oil and filter? Will using the same oil for over 6 months be an issue too?

Two keys to oil, first use good oil. Mobil 1 is probably the best commercially available oil, Amsoil and Royal Purple are said to be even better, but not as commercially available. Second, Always, and I mean ALWAYS use a good filter. Stay away from Fram if you plan to go long intervals, or replace it every 3K. Mobil1, and K&N filters are identical, and very well made, WIX filters are also very good, probably the best on the market. Something I found very funny, I bought a Mobil 1 filter for the TCH, and a week later a John Deere filter for my x500. They were both the same exact filter, down to the part numbers stamped on the case, only the DOM was different.

I have done oil analysis on my truck and cars for the first few changes to know just how long I can go between changes, which on a F350 Diesel is expensive, so I want the oil to last as long as possible. I easily got 9500 miles out of Dino in the diesel, and in the gassers, I got 15,000 out of Mobil 1 before deciding to change it, and there was still some life left in it. Remember the key to long oil life is a good filter, and change them out frequently. If you want to go 15K between changes, replace the filter every 5K.

Not sure how puralator stacks up, but it got pretty good reviews [ame=http://www.amazon.com/Purolator-PL14610-PureONE-Filter-Pack/dp/B000GIVEII/ref=sr_1_1?ie=UTF8&qid=1257350102&sr=8-1-fkmr0]Amazon.com: Purolator PL14610 PureONE Oil Filter (Pack of 2): Automotive[/ame] . If I were to go 15k with mobile 1 (are we talking the extended performance gold cap?), when I change my oil filter, do I have to drain out the oil then put it back in or can I just remove the oil filter? I have never done the latter so don't want it to come gusing out on me. Also, what is a general test I could perform say after 10k to make sure the oil ius still good. I don't even know what it would cost or where to go to get it tested. Thanks for the info so far!

I haven't heard anything bad about the Purolator, haven't heard anything outstanding about it either. Its a matter of how much media is in it and how small of a particle it can filter out, down to <5 microns is good.

Replacing the filter is simple enough, on a cold engine, all the oil will be in the pan except for what is in the filter and valleys that didn't drain down into the pan. Just remove the filter as normal, and if the filter is positioned where the open end is facing up, fill it with fresh oil, and install it, run the engine until pressure builds and top off the oil as needed. If you run the engine first though, you will lose more oil as it drains down from the head.

Good to know, I think I'll stick with mobil 1 puralator, or k&N if the price is right. Were you talking about mobil 1 extended performance in the previous post? And if not, is it really worth the extra $4 per 5 liters?

Mobil 1, the original. The only way to know for sure if it is worth the extra money is with an oil analysis. After running 10K with Mobil 1, have an analysis done. if it comes back safe to run another 5K, then the answer is no. If you run the extended, and do the analysis, and after 15K comes back that you can run another 5K, then yes. I have been running Mobil 1 for years, and every one of my engines has been CLEAN, no sludge, no deposits, looks as good as the day they were built. For me Mobil 1 is worth the extra cost.

Based on info from the oil filter study I'd say if you're planning on extending the oil change interval, change the filter only on the old interval. The study showed most filters are mostly plugged by about 1500 mi. The oil circulates via the bypass. A -larger- filter is not practical. There isn't room for it.