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Color of oil doesn't mean much; some engines will cause oil to darken rapidly while others go for thousands of miles before it gets dark. Sorry to disagree with you but any synthetic will easily surpass the 5K mark and still be good to go. Still, the only thing that really matters is what you feel comfortable with. :)
 
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Some customers have asked me to chime in, so here goes!

Stick with the factory-recommended oil during your warranty period, for all the right reasons. Once you're "on your own", so to speak, there's good reason to shift to 10W30 or 10W40. The engine's internal clearances will accommodate it, and we've had great success with it, on everything from stock to high HP Ecotecs. Plus, shifting to a non-Dexos blend gives you the opportunity to enhance zinc content, always a good thing as today's oils have been largely stripped of this helpful compound.

The relatively thin stock oil weight is mostly an effort to reduce parasitic drag, thereby increasing not only power, but also fuel mileage, as well as reducing emissions. The gains run from scant to slight, but in this game, the OEM's like GM (our engine's supplier) must play every avenue technology offers in order to be competitive and comply with federal standards of fuel mileage and emissions. The advent of super-lightweight oil has been made possible by modern engine manufacturing materials, techniques and tolerances, which have improved markedly in recent decades, as have the chemical dependability of the oil blends. This improvement in engine technology has allowed lower-viscosity (thinner) oils to be employed, which is to say that with the contemporary engine technology of 30 years ago, this would not have been durably possible.

Today, the engineers can play that card. However, their motives and prerogatives can differ from ours. Whereas they need to hit those standards, and will employ thin oil to do it, we can hedge our bets a bit, by going a bit thicker. Ultimately, the efficiency losses are quite small, and of no real concern to the average enthusiast. While the standard 5W30 does a passable job on average-duty engines, when an engine is run hard, with the generation of more heat in the oil, which affects operational viscosity as well, with the added heat thinning the oil...going even to 40 weight is a reasonable change on engines that will see elevated oil temperatures from such hard and/or high performance use.

Oil itself is an immensely complex subject, a wonderful matrix of dozens of different chemical molecules in addition to its refined crude base. There is much to know about it if one seeks same, but for the purpose of our discussion, let's focus on weight for a moment.

5W30 means a weight of 5 at low temperatures (W for winter) and a weight of 30 in typical ambient temperature (for instance 70F and up). The clever compounds within it will vary the viscosity in a proportional fashion relative to ambient temperature. Multi-weight oils were developed some time ago to address the lubrication needs of the cold engine vs. sub-freezing outside (ambient) temperature. Standard single-weight oils slowed to molasses-like movement in the cold, and engine life was affected.

As such, 10W30 will flow slower than 5W30 at the winter end of the range, but as Slingshots aren't typically sparked up on zero-degree mornings in Billings, Montana...this really isn't much of a concern. That's effectively what the 5W is intended to suit, and since we're rarely if ever going to be there, going to 10W on our cold end isn't an issue.

However, even 10W30 is still only 30 weight at operating temp, so it's no different than the 5W30 there. Thus, while an upgrade to 10W30 makes some sense, as the sloping of viscosity variation from cold to hot is still thicker overall, what I prefer is 10W40. With it we can also address the hot operating end of the temperature range, as well as the fact that we will typically be adding more heat to our oil via vigorous use and/or performance enhancement, which would further thin out a 30 weight. At that point the 40-weight will maintain better oil pressure when hot, and better shear protection under extreme pressure.

FAQ: So, once my engine is out of warranty, and fully broken in, 10W40 eh? How can I be sure that it works before I do it to my engine?

FOA (frequently offered answer): In our programs, we've been doing it for 15 years with GM's Ecotec, and have amassed a substantial amount of empirical evidence which supports the notion. Engines we've run for years at high output have been dismantled, inspected for wear, and were so good they could be put right back together, bearings and all. It works, especially once an engine has enough miles on it for the internal clearances have reached maximum oil flow. The flow of oil through an engine increases as all of its internal lubricated clearances "open up" as the initial wear takes place. Once we are out of warranty, the engine is fully "clearanced" internally, and can benefit from the slightly thicker 10W40...especially if you are going to work it harder than just putt-putting about!
 

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Sorry to awaken a REALLY old thread, but Amazon Basics 5w-30 full synthetic is dexos approved and is a re-brand of a very very old and experienced oil company. Project Farm (You Tube) did a bunch of oil testing and reviews (including sending oil samples to Black Stone labs) and Amazon Basics full synthetic beat I think everyone but Penzoil... Kind of cool
 
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