After reading all the oil related threads on lotustalk, I found nothing decisive to make me want to get one of the various top oils over another, so I decided to do some research for myself. After checking the spec sheets of the various top candidates, Mobil, Amsoil, Havoline, Castrol, Valvoline, Royal Purple, and Redline, I still didn't find anything convincing enough to make me want to buy one versus the other. So I made a few calls.
First, I called Lotus USA, and spoke to their tech guy, who was very nice and helpful within the limitations of his experience and what it is proper for him to say. Basically, as you would expect, he said the Havoline synthetic 5W-40 is the oil that Lotus has done all of their testing with, and that they know is fine. He also said that Castrol synthetic 5W-40 was acceptable, and would not invalidate any warranty. He stated that the oil must be a
synthetic 5W-40 to maintain the warranty with no questions, and that other oils may or may not be an issue. I specifically asked him about Mobil 1 0W-40, since I personally think it's a great oil, but he recommended against using it since it was outside of Lotus's specs.
While checking the various oil companies data sheets, Valvoline's Synpower HST stood out with what looked like some very impressive specs. The specs were quite different from the non-HST Synpower. When I checked, no one had Synpower HST available, so I called Valvoline. They told me that Synpower HST is a special formula made to certain manufacturers' specs like MB and Porsche, and is not available on the retail market. Apparently, only dealers can get it, and only in bulk drum quantities. Also, as far as the guy I was talking to knew; they have no plans to market it through retail outlets in the future.
So in the end, I decided to go with the Lotus recommended Havoline synthetic 5W-40 since the difference in specs between the different oils wasn't enough for any to stand out, there would be no questions asked from a warranty perspective, and the price was right. I found the local distributor through the following link
http://www.texaco.com/worldwide/nort...er_locator.asp which I found on one of the threads here on Lotustalk. The price through them in 6 quart case quantities was $4.70 per quart.
The local distributor's service was outstanding! They delivered the oil directly to my house the next day with no charge for delivery.
They also faxed the data sheet for the oil to me, which is a little bit different from what was previously posted in this thread, so I've attached that, and the Valvoline Synpower data sheet as well.