2002 Envoy 4.2L M1 0W-40 Euro/15W-50 mix 1,200 miles

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May 4, 2008
The story on this engine can be found here: https://www.bobistheoilguy.com/forums/ubbthreads.php/topics/5161992/1

Current mileage just over 292K, only rod bearings and lash adjuster replacement.

This is my DD, about 30 miles each way to work, 70/30 Hwy/Cty.

I wish I had done these UOA's earlier but short story....after the rod bearing replacement, I spent a week cleaning the piston crowns then filled with Supertech 5W-30 and idled for an hour or so then drained. Refilled with PUP 5W-30 and drove for 1,100 miles and started to hear a slight sharp tap, may have been an exhaust manifold bolt that backed out. Thinking the oil may have thinned I changed out the PUP earlier than planned at 1,100 miles and went with a mix of M1 0W-40 Euro & 15W-50.....6 qts 0W-40 & 1qt 15W-50.

I have a light piston slap (I believe) when cold then almost completely smooths out when warm which has been decreasing with mileage. The noises have come and gone, maybe the rings have cleaned up now and could be the result of hearing less noise.

I added the 15W-50 mainly because I thought I needed a dose of magnesium...maybe I don't.. and also to boost the viscosity slightly and again...maybe I don't need to.

I confess that I botched the VOA of the M1 home brew by not mixing all 7 qts and sampling from that batch. Instead I used two separate bottles and even though I shook them up, may not have drawn enough oil to get a good reading. I will redo the VOA next oil change.

My possible botched VOA of the M1 home brew, posted to help link the analysis of the UOA. I doubt the lab got this wrong.

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Here's the current UOA, the PUP 5W-30 is on the right of the grey column and the M1 brew is on the left. The M1 is still in the engine and will re-sample at 2,400 miles.

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In the UOA, calcium and magnesium seem lower than I'd expect and molybdenum is much higher. You've been getting some questionable results from Blackstone recently. I would try Polaris or some other lab in the future.
Originally Posted by JAG
molybdenum is much higher.

Yeah....that part also struck me as odd. I don't think I've seen any VOA of those two oils having remotely near those levels of moly, unless I missed something.

I agree it's worth looking into since this batch of UOA/VOA's I sent in has some noticeably skewed figures in some areas.
The only thing that comes to mind was having used the Permatex Ultra Slick for the new rod bearings. However that was with the initial fill of PUP 5W-30.

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