I got my car back from the shop, and quite frankly, it seems peppier. The car runs faster, the needle looks faster and I can feel it in the seat of my pants... Does Oil have this much of a profound effect?

Find out what grade oil your shop used. If you regularly use 15W-50 and your shop put in 10W-30, then there would be a significant difference (5%+) in engine acceleration. However, if this is the case, the car shouldn't use an oil as thin as 10W-30 (which many corner shops use by default) in ambient temperatures over 40-50deg F. I'd ask. Also, the thinner oil may not protect your engine as well as a higher viscosity would.

Also on a side note, some people notice increased power when they change to synthetic, but I'm sure you'r shop would have asked or told you about that.

ATLD

Nah, my car gets its oil from a dealer, 15w-40 all the time.... I don't even think 10w-30 is a endorsed oil for a diesel like mine.

The only way oil would make a really perceptive diff,would be if you spilled it on a steep mountain downhill and than drove the car on it.

I recently changed my oil with Castrol 20w-50 and my 82 seems to have had a signifigant increas in pep. At 241,000 miles, I believe the thicker oil is best...At least in the warmer SoCal climate.

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1982 300D Turbo "Helga"
380,000 miles

New oil of the save nominal viscosity may make you feel that.

As old gets old, I think its viscosity increases (thickens) due to soot, and wear particles, and other stuffs.