Originally Posted by Or
A cheap oil would be a bad idea, as the problems will get worse. As you know, they have oiling issues. The '97 much less so...
I have a '98 SLX, which has the more problematic 3.5l. It has more consumption issues vs a 3.2l because of bad drain design in the OC ring and piston skirt. The 3.2L you have is OK in this regard, but some internal passages are too narrow and create issues, which is common on both engines. Camshafts can get starved from this so it is not a trivial thing. More robust 10w30s (which is what Isuzu says to use) definitely are better than 5w30s and your climate does not demand the 5w30.
Since you are inheriting someone else's maintenance and have no idea what it is, it would be VERY wise to do an engine flush or two. I have had great success with idling with kerosene for 20 minutes before draining the oil. A blocked passage I had in the left cylinder head is now good. I've tried a lot of oils and I buy the Mobil 1 10w30 HM in spring and fall when on rebate (it is now), so it is $13/5 qts. and that feeds the beast nicely. I also add a few ounces of lubegard biotech and that has made a noticeable improvement. My 98 would go through 1qt in 400 miles like scrier said. BUT, with piston soaks and engine flushes, and a strong 10w-30, I now go through 1qt every 1200 to 1500 miles. 10w40 doesn't help and I've tried a lot of oils over many years and settled on the M1 10w30 HM as the best compromise in this engine. Given how cheaply you can get it buy shopping smart, it's also plenty cheap enough. My valve guides were also leaking a bit, and the M1 HM cured that with no other intervention by me.
You are probably loosing a decent amount of oil via the valve cover gaskets, spark plug seals, and cam shaft seals by 150k miles. It is almost certainly due or overdue for new seals up top. The 3.2l does not have the piston issues and excessive burning like 98+, so your losses are most likely leakage + normal consumption, and be manageable if you fix the leaks.
Who's running that special on M1? I will stock up.