Originally Posted By: CATERHAM
Originally Posted By: Swift101
My logic for using a heavier oil is to extend my OCI past 3.5K, preferably go to 5K (max allowed by Hyundai). I've seen many reports showing products like PP 5W-30 shear out of grade after 3200 miles. I know shearing might not hurt anything but I'm sure it's not ideal.
And your reasoning is entirely flawed.
Firstly, Hyundai doesn't even specify that synthetic oil be used, so electing to use a premium synthetic which is clearly more shear stable than the most shear prone API dino gives you an increased viscosity margin.
Secondly, it's not oil shear that you have to be all that concerned about to warrant running a heavier grade but rather very high oil temp's, and since you're not tracking your car extreme oil temp's aren't going to happen.
Finally, even a shear prone 5W-30 will still provide plenty of viscosity reserve. You're making the common newbie error that it won't, in effect second guessing the engineers, and therefore blindly assuming running a heavier grade will provide a lubrication advantage when the reality is the opposite.
The best approach one can take for a street driven car is to run the lightest oil specified for the engine and if a synthetic oil is not specified then use one for additional high temp' protection plus other benefits.
If you're serious about high performance driving then install oil gauges which will enable you fully monitor the operational viscosity of the oil you're running. In so doing, more often than not you'll find that a lighter oil grade than specified will often work optimally and very rarely a heavier oil grade even with track use.
I don't know if there is a reading comprehension issue here but I for one see the OP's logic as sound.
These are the facts that I get out of the OP's posts:
Hyundai recommends a 3.5K OCI for severe service driving and 5K OCI for normal service. Under the guidelines of "severe service" that is what the OP must follow based on where he lives, type of trips taken, etc, etc. So, under his service, with a 5W30 synthetic, at 3.5K OCI's, it has sheared down quite a bit, likely due to fuel dilution. He wants to push his OCI to 5K, even though the limit is 3.5K, and at that short OCI, he has found a considerable amount of oil shear. He wants to step up to the also RECOMMENDED grade of 5W40 synthetic such that he can extend his OCI's to 5K, despite severe service, and no doubt, lots of fuel dilution causing oil shear over that 5K.
What exactly is flawed about his reasoning? Nowhere did he ever mention high oil temps, or racing, etc. He is going up to a grade that is recommended by Hyundai in order to extend his OCI in an engine known for fuel dilution and extreme oil shear in normal, mundane driving.