3.5L Oil Consumption issues
Here's a paraphrase of something Jerry Lemond wrote in a forum topic titled: "Rotella T Results for Oil Consumption" from Aug 25, 2007 on this issue.
Starting in 1998 on the 3.2 and 3.5 Isuzu made the oil control rings less thick to decrease friction. They also drilled only 2 drain back holes on each side of the piston (inside the land). Why do we need holes inside the lands of the oil control rings? The oil that lubricates the cylinder wall comes from the crankshaft rod journal, where there is a hole drilled to align with a hole that’s drilled on an angle in the connecting rod that goes all the way through and exits near one of the rod bolts.
This hole is drilled and aligned in such a way that it only delivers oil on the cylinder walls as the piston is coming down from TDC and only on the major thrust side of the piston (which is the intake side of the piston), and why some pistons are directional and one of the reasons they have FRONT markings on them). As the piston descends the oil control rings job is to scrape the oil off the cylinder walls but leave a small amount for lubrication. If carbon begins to build up in the oil control ring area the rings are not free to move and function as they should.
The cure is to use a hi detergent oil but that will not break down the carbon in just 1 or 2 oil changes, it takes a lot more time. Rotella oil is a high detergent oil but it could take 8-10 oil changes before you see an effect.
In 2002 Isuzu addressed this oil consumption problem in the 3.5L by drilling 4 oil drainback holes. If you compare a late 3.2L side by side with a late 3.2 or 3.5L you’ll find a height difference. The 3.5 has a longer stroke, so the pistons are shorter in order to fit in the same deck height, the piston pin had to be relocated higher and the skirt was shortened by about ½ an inch to keep from hitting the crankshaft. The older engines had a 4mm wide oil control ring and 4 very large drain back holes on either side of the piston, the late engines have a 3mm wide oil control ring.
From J-Dawg dated Mar 27, 2008 of same thread:
If you are having problems with oil consumption, here are some commonly recommended steps:
1) replace PCV valve and air cleaner element
2) clean EGR system -- both valve and feed pipe that runs into the intake manifold. Check the FAQ or search for procedure. Be sure to clean the pipe.
3) Run a high grade full synthetic motor oil.
4) Run a high grade full synthetic diesel-rated motor oil.
5) Run a Seafoam or Auto-RX or similar oil treatment.
6) Perform a compression & leakdown check.
7) Rebuild engine and clean or replace pistons with newer designed OEM replacement pistons with larger and more oil drain back holes (your 2002 should already have them).
psguardian on Oct 22, 2010 in a thread titled "Burning Oil Fix for Late Troopers" said:
Issue: 3.5L burns an unnatural amount of oil, even with good maint.
Cause: Piston design flaw, the recess for the oil scraping ring only has 4 drain holes.
Fix: late production in '02 Isuzu changed piston design to include 10 drain holes in the oil scraping rings recess. (plus regularly changed oil)
Apparently the later 3.5L (some say later production 2002, others say all 2002 models) with the increased number of drain holds have a PCV valve that screws in. The earlier ones pressed into a rubber grommet.
