PU 5W30, 5350 miles, 56076 miles TBSS

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This is an odd sample from my 2008 Trailblazer SS LS2 at 56k miles. Its the first sample that I've taken since 2011 since it was very consistent before. The high iron has me a little concerned. This may not be relevant, but the strange thing is that I sent in a sample for my 2009 Chevy Cobalt SS/TC just a week prior and it too showed high iron (although only 37ppm), which was not in line with the ~ 40k miles worth of prior samples that I have. Only thing that I can think of that the two cars share is the 92-octane fuel that I get at the local Shell station (oil is not same nor is usage). Could this be coincidence or is high iron suddenly in my fortune cookie? Some details on the TBSS usage - this is our fall/winter daily driver. Usually it sits in the shop over the summer months and only occasionally gets driven/started (maybe once per month). This oil sample was taken after largely sitting in storage for about 5-6 months over the summer if that makes any difference (vehicle was started and run to operating temp prior to sample FWIW). During this time it was started and driven occasionally (maybe every couple of months). The engine runs like a champ and when it is driven it is about 75% highway - no racing, no hard use, etc., and all stock internals. Any thoughts on why suddenly high Fe might show itself?
 

Fulton 1

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Originally Posted By: steve20
reference prior tests--boron = 300+ was this an additive you were using which came back to cause high Fe levels later on?
Nope. No additives used. For reference, the prior samples were as follows: 11/13/10 sample - M1 5W-30 02/26/11 sample - PP 5W-30 10/08/11 sample - PU 5W-30 There are some odd differences between this latest UOA and the one on 10/08/11, which was same oil type, same filter type, etc.
 
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Fulton 1

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Correction: the 02/26/11 sample was also PU 5W-30. I've never run PP in this vehicle. Nor used any oil additives.
 
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Fulton 1

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Interesting observation on the boron. The two samples with the higher boron levels were the old PU that I used to get in the the 5qt Walmart jugs. The most recent sample was the last of my PU stash, which consisted only of PU quart bottles, some of which I had picked up on closeout at Walmart and the remainder I had purchased at a local Autozone. There must have been a formulation change around that time. Do you guys think there's a correlation between the reduction in boron level and the increased iron number? At any rate, I changed the oil when I took this last sample and went am now using Redline 5W30 since that's what all my other vehicles are using and I have a large supply. My plan is to re-sample in a couple thousand miles and see what it looks like at that point.
 
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