If you guys are using mobil 1 or anything else that is not a true synthetic then I would change every 5k miles as it is somewhat synthetic and lasts longer than conventional oils. If you use any of the true synthetics like mobil 1 extended performance, ams oil, motul, redline then I would go 10k miles. Changing oil nowadays every 3500 miles seems a bit excessive unless you are using oil that costs $3 a quart, but it is your car and it doesnt hurt to change it early.
This has been discussed in several other threads over the years. While it is true that
most Mobil 1 oils sold in the US now contain Group III components (severely hydrocracked mineral oil), in addition to Group IV PAO and Group V Esters, I am not sure about the information you presented on other motor oils (even though I realize it is taken as gospel on other forums).
Redline also has substantial Group III components.
Amsoil makes three different "synthetics" and only one of them uses
only Group IV and Group V, and it is not API certified, and does not meet Hyundai specs for that reason. This is the classic bait and switch routine, where the only oil performance reports they publish are for the highest quality one, which most people don't buy because it is very expensive and not API certified.
I don't know about Motul.
Most synthetics sold in the US, including those from Pennzoil, QS, Castrol, Valvoline, etc, have
no Group IV or V components (except maybe very small amounts in the additive package), and are entirely Group III. Mobil 1 is mix of Group III, IV, and V.
The amount of Group III, IV, and V components in Mobil 1 varies by the viscosity and the name of the product. For example the Mobil 0W-40 is entirely Group IV and V since it is designed for use by German cars. Although Mobil 1 Advanced Fuel Economy oils have some Group III, they have more Group IV and V than most regular Mobil 1. As noted, Mobil EP has a higher amount of Group IV and V, but I believe it has some Group III also.
Due to advances in refining technology, Group III synthetic (severely hydrocracked mineral oil) can be made to closely resemble Group IV and V synthetics in terms of chemical structure and performance. Shell (including Pennzoil subsidiary) now makes Group III entirely out of natural gas. As you said, these are fine for 7500 mile or less oil changes, and significantly outperform conventional Group II motor oils as specified by Hyundai.
Hyundai, fearing that consumers will think that their cars will cost too much to maintain, still only requires Group II conventional oil. Toyota and Honda now require synthetic in almost all their vehicles, since they specify 0W-20 instead of 5W-20, and 0W-20 is only available as a synthetic.
