Originally Posted By: bigblumer
You can't compress a fluid, so its not the oil. One brand of oil can't compress more than another. If you see a drop in pressure, you have a mechanical (parts-related) problem somewhere, rather than a hydraulic (fluid-related) problem, assuming you have enough oil in the pan.
That's not really true. It's not compressibility that matters, it's the viscosity. If for some reason the viscosity was less than it should be then you could get reduced pressure.
Like "zerosoma" said above however, in all the tests we've seen from places like PQIA the major bands (including valvoline) are always in spec for both additives and viscosity specs. It's only off brands like for example the two that zerosoma mentioned that sometimes have way off spec viscosity.
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If the problem happened at the exact same time as the oil change, then I would start with changing the oil filter. Its a cheap way to rule out one of the causes to your issue.
Yes, this I agree with.
The other thing is that the OP still hasn't told us what brand/viscosity oil he was using previously.