In light of the healthy amount of discussion, and amount of repairs/failures that can be attributed directly or partly to lubrication on our little 1.4's, I offer a few observations:
First, my car's engine has been nothing but dependable, low-maintenance, durable, and consistent since I got it with 454 miles on the odometer. I attribute this strongly to my attention to what fluids go into the engine. The oil was changed first at 1,900 miles, then 6,000, and every 5,000 after that until 50,000 when I switched oils. (More on that in a minute.) It hasn't seen GM brand oil or synthetic blend since I used up my 2 free changes, during which time I observed slightly longer warm-up and cool-down times and other traditional break-in habits to some extent. It's also seen less than 30 gallons of regular grade fuel its whole life, most of the time drinking 89 with 91/93 every so often and a can of Seafoam in the tank every 10,000 miles.
I trusted and used Valvoline products for quite a while before buying the car - it's the brand (MaxLife syn blend) my dad used in his '97 Suburban from purchase (2006/170,000 mi.) to now, which sees it at 410,000 mi. and counting with no service to the long block and consumption of about 1,500 mi./qt. So I chose Valvoline SynPower from a combination of my confidence in its quality, and availability. The only time I've seen the car consume ANY oil is on long trips when conditions were particularly strenuous, causing only minor (maybe 1/8" on the dipstick) loss - otherwise, oil level is the same when I drain it as when I filled it. I've never done a UOA or added anything to the oil between changes, and use nothing but Wix or Delco filters. At 52,000 mi. I switched from Valvoline to Schaeffer's Supreme 9000 and extended my OCI to 7,500 mi. because I've had good experience (though limited) with Schaeffer lubes, know several savvy mechanics that use it exclusively, heard good things about their product on forums, etc., and it's more available where I live now in Kentucky than it was where I lived in Missouri. At that time the car was seeing roughly 75% sustained highway-speed miles with me at the wheel and I had no pause about running the oil that long - after all, it's a high quality full synthetic that I was draining at the interval the OLM would've had me draining a synthetic blend. However, the last couple months my wife has been putting most of the miles on the car, and having just poured in the third dose of Schaeffer's I'm going to start draining it at 6,000-6,500 for several reasons:
1. Upon inspection I'm seeing a few small traces of varnish developing under the valve cover.
2. Through observation of the economy pages on the DIC, it seems my wife averages 3-4MPG less than I would in the same conditions. (Bless her heart, her foot just isn't as steady as mine and she doesn't have the feel for the sweet spots in the power curve that I do.)
3. During the 5,000 mile OCI's the oil would be all the darker it was going to get by 3,000-3,500 - 60-70% through its life. Now with my wife's foot, more stop-and-go driving, and a 7,500 mi. OCI, it's turning black at least as quickly but staying in 50% longer and on toward the end of the change interval it feels, well, just less slippery. (That may be in my head, but what can I say. This engine runs like a Swiss watch and I'm willing to err on the side of caution to keep it that way.)
To lay out my reasoning (while not as educated and scientific as, say, Xtreme's opinion, but...) that's based on more than a little study, experience, and observation, here's a few points in Q&A format more or less as I mentioned them above.
Why was I so quick to get away from GM, and syn blend, oil?
While it may not necessarily be bad oil, the manufacturer has a vested interest in using not the best lubricants, but adequate ones. As long as their formulations and intervals keep the engine in one piece past the warranties, the longer the car lasts after that the more money they lose. When I bought the car I examined several points of the engine's construction - a turbocharged, relatively high compression, high-redline, small displacement mill that certainly has its work cut out for it moving a car that weighs from 3,400-4,000 lbs. depending on contents. Gas+turbo pointed me straight toward full synthetic, and I erred on the conservative side of the manufacturer's OCI recommendation and felt it was a very good decision but not so conservative that I was undeniably wasting oil.
If I put such a priority on good lubrication, why not use Amsoil?
I'm solidly of the opinion that Amsoil is the best stuff out there. Actually, too good for my car at present. If the car was driven very frequently on long trips, rolling the odometer like a slot machine in clean, economical, low-wear situations, a 10K OCI with Amsoil might be more economical and appeal to me more, but since the car sees more than a little stop-start, short trip use and the little 1.4 spends so long trying to warm up in cold weather (which would be over half of one of two annual 10K OCI's) running dirtier and contaminating the oil more, I'd rather flush the oil more often and doing that with Amsoil is just a waste. If this was a hi-perf. engine or it was tuned/raced, I'd be inclined to think differently, but compared to the stresses seen in racing it is just a stock, standard-performance engine that's designed to perform with much poorer lubrication than I already give it.
(However, for anyone who hasn't yet, or is on the fence about, changing their factory-fill manual trans. fluid to Amsoil, just do it. After some apprehension, research, and observation of others who changed the fluid, I swallowed the fears of a voided warranty and changed to Ams 5W30 synchromesh at 30,000 mi. and, after almost 40,000 miles, have no doubts it's the way to go. So put the pin back in your potential grenade M32 and get that nasty factory fill outa there ASAP.)
Why don't I use regular grade fuel?
Because the few times I've put 87 in it I immediately regretted it. Some Cruzers, even non-tuned, will run nothing but top-tier premium. Based on a lot of scientifically calculated, close observation running the car on premium vs. plus, I can't see much difference. I don't have an Ultragauge or anything where I can monitor engine temp, boost, and timing fluctuations related to octane, but I've paid attention and I've never been able to discern a notable difference in performance or economy between plus and premium gas. I'm not bleeding money, either, so the "peace of mind" (which I don't see much of in 91/93 over 89) isn't worth the 15-25 cent difference when I can't find anywhere near an equal reflection in gas mileage. However, this car has only reinforced my preexisting opinion of regular grade ethanol gas. Each time I've put any in it I've been surprised by how much differently the car performs, finding fuel economy trending 1-2MPG lower and disconcerting lack of power when I expected to have it. Feeling the car start to develop power as I accelerate to pass, then feeling it take a noticeable dive right when I need it to keep pulling to get around my "victim", forcing me to grab another gear to make sure I make it back into my lane in time, isn't a great feeling from a car I've grown accustomed to being very consistent and dexterous.
My habits and priorities are purely my own, disagreed upon by some and not practical for others. But I feel my car's exceptional performance and lack of need for repair in the face of the 1.4's debatable reputation is largely due to those habits and that's why I offer them in such detail for other owners. Happy Cruzing.:th_dblthumb2: