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I'm betting your engine is sludged up by the previous owner using low-quality oils and/or too long of oil change intervals and the detergents in the "good" oil, your Valvoline Synthetic, are breaking up the sludge.
My '08 must've had a little build-up in it cuz ever so often, maybe 4-6 times between 5K-mile OCIs, it had a lifter ticking for a few seconds after a cold start. I used Mobil1 for the first change or two after I bought it then Pennzoil Platinum ever since. I can't recall the last time it ticked and the old oil has been coming out noticeably lighter.
Just my theory.
I've been looking into this more. Because the bypass is built into the adapter, the oil filter itself has no bypass.
I forgot what oil filter I used last summer, but it was from Canadian Tire. I usually get Wix, but CT does not have Wix so I had to go with a different brand that time. I would not have purchased Fram, I doubt I would have gotten Motomaster. This leaves K&N, Mobil 1, or Quaker State. I'm pretty sure it did not have the welded nut on the end which eliminates the K&N. That leaves Mobil 1 or Quaker State. I suspect I got Mobil 1 which is an "extended performance" filter.
This is where things get interesting. The regular duty oil filters (Wix 51042, ACDelco PF46) have a filtration efficiency in the range of 20-30 microns. None of the "extended performance" filters have a filtration efficiency listed anywhere on their respective websites that I can find. However, they seem to advertise that they can get away with longer service intervals. The only way you could get away with longer service intervals would be to allow better flow as the oil gets dirtier. Either the surface area would have to be greater to collect more particles, or allow some larger particles to pass through the filter. Or, there may be some other way that I'm not familiar with yet.
When I switched to Valvoline synthetic and the Wix 51042 2 years ago, my oil pressure started dropping drastically and I had a cold engine knock that lasted progressively longer. I changed the oil and filter and found the filter was all sludged up inside. After the oil change, my oil pressure returned to normal and was pretty good for the next few months. Then we pulled a 3500 lb trailer to Kamloops which involved some 12% grades. I would hold the engine RPM's around 4000 to keep fluids moving faster to help with cooling. I never actually overheated, but the engine temperatures did rise from the usual 95°C to about 110°C. When this happened, I made every effort to reduce the engine temperatures (turned off the AC, turned on the heat until temperatures dropped). After the trip, the oil pressure had dropped from the normal 40 psi to about 30 psi. Time was short, so I purchased the oil filter from Canadian Tire and only changed the filter. This returned my oil pressure back to the 40 psi. It remained at this 40 psi until Christmas time when I changed the oil.
It was this oil change that I found the really bad sludge. I was shocked that my oil pressure was showing normal with such bad sludge. I has assumed that the Canadian Tire oil filter had a bypass, whereas the Wix and ACDelco have no bypass in the filter. That assumption was incorrect. All filters for the 5.3L (for the 2002) have no bypass. What I think was different is that the oil filter I used was the extended performance filter.
At this time based on what I know, I will not be using any sort of extended performance filter. "Extended Performance", "Heavy Duty" etc may not mean better. Unless some one can teach me otherwise.
As for the source of sludge, it could have been increased oil temperatures on the trip to Kamloops, it could be a head gasket leak allowing coolant in. I have ordered an oil test kit to test the oil. There is also a test kit to test for combustion gases in the coolant. I will see if I can get some one to test that for me, or I might get a kit.
I'm betting your engine is sludged up by the previous owner using low-quality oils and/or too long of oil change intervals and the detergents in the "good" oil, your Valvoline Synthetic, are breaking up the sludge.
My '08 must've had a little build-up in it cuz ever so often, maybe 4-6 times between 5K-mile OCIs, it had a lifter ticking for a few seconds after a cold start. I used Mobil1 for the first change or two after I bought it then Pennzoil Platinum ever since. I can't recall the last time it ticked and the old oil has been coming out noticeably lighter.
Just my theory.
Can't remember if we talked about this before but is there some reason you went with the penzoil over the mobil?
I agree with this that the sludge is from the previous owner, but I am partly at fault myself. I should have changed the oil right after my Kamloops trip. My Tahoe does not have the oil cooler, so I'm pretty sure the oil got cooked a little even though it was Valvoline synthetic. Either that, or the trip cleaned out a ton of sludge.
I see you're in LA. Cold for you is warm for us! Dry for us is Noah's flood for you!
My current concern is that I'm leaking coolant into the oil. If I am, it can't be much. I don't have any drivability concerns at all. I have an occasional miss that may be a failing coil (I have yet to swap coils to check). If the current sludge is due to a coolant leak, I will have to fix that soon unless I want to be replacing an engine. What shocked me this winter was the sludge I was getting, but the oil pressure was normal. I'm even wondering if the filter media was faulty.