Originally Posted By: Bloodknights
This is probably a dumb question but can a thicker oil then required cause your tranny to shift abnormally,or does one have nothing to do with another?
Yes, absolutely so. Engine and transmission problems are very closely related, as the two work in tandem. Thicker engine oil results in sluggish low-throttle response because of increased engine friction, which in turn results in harsher transmission shifts from first gear to second gear at low throttle. That's because the decrease of engine output power due to thicker, high-friction oil will affect your programmed transmission shift points, which assume a certain engine output power. You may not notice this in powerful engines or with small viscosity changes, but it's easily noticeable in my car when I use 15W-40.