I won't go into why this happened (long story) but my son's 2.2L S10 oil didn't get checked for about 4000 miles. He was driving home today on a 80 mile freeway trip when he noticed it felt like he didn't have full power, yet it would maintain road speed. The oil pressure which normally runs around 60 psi was at 50 psi (idle normally 20 psi was about 13 psi). Ambient temperature was close to 30F.
We checked the oil and it was down, possibly as much as one quart below the safe (hatchured area) of the stick. There was clearly oil on the tip of the stick (about half inch of it), and it did not smell burnt.
We added about 52 oz of oil (maybe less as spilled some in an overflow of filler tube) so that it was showing on the stick close the full mark. Hard to tell because of residue in fill tube (stick is in fill tube, oddly). Drove it about 4 miles and every thing sounded fine and he had normal oil pressure again. Can't discern any bad engine sounds.
I can explain the low oil pressure as the remaining oil would have run a lot hotter. But the feel of slight power loss is disconcerting. I am afraid he may have had some extra bearing wear if either the oil film was compromised and there was any metal on metal contact. But maybe just the thinner oil from extra heating resulted in more friction.
At any rate all seems good now. Any thoughts? What to do next?
The oil I added was close to a quart of 5w30 (minus spillage) and about 20 oz of zddp booster (@ 4700 ppm zinc, 4300 ppm phos, 7800 ppm calcium, and 28 cSt at 100C). My thinking was that the extra zddp might be needed at a time like this if there indeed was any metal to metal contact.
So, where to go from here? Not sure oil analysis is of much value since any damage, if done, is done. But how long should I run this oil, which had 5000 miles on it but is now about half refreshed? I was thinking to get it out of there in a few hundred miles in case there is extra metal residue in it. Then run one or two loads for say 3000 miles, before going back to a 5000-mile OCI.