Sorry for being long-winded, but I feel all is pertinent info, there's a lot of maintenance pics but just hoping to possibly answer as many questions as possible beforehand. I've had a few threads on this in the maintenance section but this will be just for the oil. Brief history, 2002 Envoy, currently I'm at 290K, I bought this new and used Mobil 1 5W-30 for almost all of the first 200K. I developed a slight lash adjuster tick when cold then tried a few other oils...some T6, some HM 5W-30, but mainly stuck to the Mobil 1 5W-30. Over the course of the last 30K, the motor went through a short series of occasional ticks and taps, nothing major. Around 260K I installed an oil catch can, this may or may not have caused a few issues but it certainly didn't help in the end. During my OCI's of about 4-5K miles, the can would catch about 4oz of oil, and at each OCI, I would dump the oil and move on. After about 4 OCI's, the can would catch less and less, until there was enough to cover the bottom of the can @4K miles. I didn't notice much difference in the noises until about 280K. There was some more pronounced tapping noises and a more prominent hard tap when warm which gave me concern. At this point I tried a dose of MMO, then some Rislone...seemed to help a little but the hard tap just lingered. Recently around 287K I checked the large fresh air port for the PCV on the valve cover and discovered there was practically no vacuum. I investigated further and discovered the port at the crankcase was plugged up, turns out there was a small filter in the lid of the catch can that plugged up thus causing a total PCV clog. I was also hearing a much more intense knock from just a hard tap when warm, at that point I drained the oil and discovered a very light silver streak on the surface of the oil, so that's when I decided to stop driving it. Good thing I did as two rod bearing halves had a small chunk taken out but no damage to the journal. I have since fixed that problem, currently using the stock PCV system, valve train was very clean, bottom end not too bad, I suppose the rings were caked a little as I developed a mild piston slap when warm. Valvetrain @ 288K Piston #1 was the worst as far as buildup: After the B12 and GM TEC: After 2 tanks of Costco 87 and 2 treatments of Amsoil PI, roughly 600 miles: Cyl #4 rod bearing had the highest wear based on plastigage @ .003: Cyl #5: Cyl #3: None of the rod journals had a mark on them, all looked like this all the way around. Cyl #2 had the worst scuffing, Cyl #4 was close: https:/
I changed out the rod bearings @ 289K, they were pretty much at .003 where max wear limit is .0025. The hard tapping noise was much less but some was still there. I pulled the plugs to find carbon on all the crowns, during that week I soaked the rings with B12 about 3 times, followed by some GM Top Engine Cleaner in the aerosol can. Since the piston soakings, the hard tapping or light knocking has almost gone away. Only very mild piston slap when cold, and when warm, very light piston slap and you have to know its there to hear it....this is progressing week by week for the better.
Once I cleaned the ring packs, I ran some PP 5W-30 for about 2 days then drained and refilled with PUP 5W-30, the PUP has been in there for almost 900 miles and the motor sounds real good, any internal noises have diminished so much that again, you have to know you're listening for something when it's hot.
When starting up cold, there is a few min where the piston slap is audible and likely due to some skirt wear, this is where my question is about going to a slightly higher weight oil. The slap, or tap, whatever it may be....likely slap, doesn't seem to fully go away. The slap comes and goes and from when I first drove it with the PUP, the slap was noticeable all the time to the untrained ear, now it has diminished about half of what it was. Right after the soaking, I could hear the slap just slightly inside the cabin, now I have to try to hear it and really it's almost inaudible.
Will it ever go away...probably not, but to the point that the motor can live for a while longer that's hopefully what I can accomplish.
So my plan is to use the PUP 5W-30 for awhile longer, drain and refill with PUP 5W-30 and get some UOA's at 500, then maybe every 500 for awhile. Should I stick with the PUP or maybe go with M1 0W-40 or a 10W-40 for the summer? The manual calls for 5W-30 or 0W-30 so the 0 weight is allowable but have to factor in mileage. I'm very curious as to what the next 2-3K miles brings to the table.
I'm upset at myself for not checking the lid, but it was down and out of direct sight....the kicker is the motor could have been fine if I left it alone..hard to say but lesson learned.
Very curious to what you all recommend given these conditions, MPG is as good or better than it has ever been, motor runs very smooth. Compression before the ring soaking was between 197-210 PSI with 197 on Cyl #4 which had the very light thrust-side cylinder scuffing. I haven't done a subsequent compression test yet. www.youtube.com/ watch?v=iDBpzP4QbaY