Over the past 5 or so years of reading and posting on these type of Isuzu boards, I have seen way to many blown engine/mega oil eater posts. Keep the EGR, PCV, EGR tube and rings (with Chevron Techron or sea foam) clean. Keep in mind of the 1qt/1k spec in your manual. Where is that oil going if there is a spec like that? Carbon build up. So keep the inners clean an you'll keep on Troop'en for a long time.
http://www.geocities.com/endre_rl/isuzufaq.htm#faq4
My truck seems to use a lot of oil, why?
Oil usage. Yep Isuzu states that 1qt/1000miles is within spec. So the key is to keep an eye on your oil. The most common ways to decrease your oil consumption is to clean your EGR valve and tube, EGR port (behind the intake butterfly) (link to a how to clean the EGR), replace the PCV valve. Also, trying to keep the rings clean (add Chevron Techron Concentrate® every 3k, and once a year add a half can of Sea Foam® to the oil (following the directions). Dirty rings (holes in the rings) are the main cause for oil usage. The 98-mid00 have fewer and smaller drain holes in the rings as compared to the 93-97 3.2L rings. The second part of 2000 Isuzu put in rings with more and bigger holes, but there still seems to be many 2000-2002 Isuzu’s that use oil.
Oil usage commonly increases while driving the truck hard, including during highway interstate conditions. If your taking a cross country trip, check your oil every time you fill up with gas.
If you take many short trips with your truck, make sure you change the oil at least every 3k. If you don’t run the truck (or any vehicle) at least 30 minutes every time it is started up the oil breakdown products are not able to boil off and can cause sludgeing (which can clog those oil rings).
The Isuzu service bulletin regarding excessive oil consumption (> 1qt per
1000 miles) is service bulletin # IB00-01-5002.
As for Oil useage, I was reading my CD manual last night, and it stated the following reasons for increased oil consumption: 1. Dirty EGR (system) 2. Dirty PCV 3. Carbon up piston rings 4. Long highway trip 5. Towing