There have been many "causes" of oil consumption, but I have only had experience with one of them. I wouldn't say that it's a failure of the 3.5L motor, it's just one of those things that you have to keep up with.

First off, stay away from Dennis Isuzu on Morse Rd. (I used to live in Columbus). They have zero clout with Isuzu, and they really don't care to work on them.

If you're not seeing the typical problems associated with a leak or 'burning' oil (out the tailpipe -blue smoke), there's another way to lose a lot very quickly. Our Dragon blew through a few quarts in one fillup (I check the oil at every gas stop). This just came out of no where -we drove it from Ohio to Alaska and didn't lose a drop. One day, it was just super low.

After jamming my head in between the engine and the firewall (on the passenger side) I found the source of the leak. It was a very high pressure jet of oil, it sprayed 1-3" before hitting the EGR pipe/exhaust manifold area and vaporizing. It made very little smoke. I was only able to see it with a flashlight at night. It was very cold (about 0F) and that helped me to notice the vapor. I also got a bit of hot oil on my hand -not the recommended method of finding a leak. I decided that a valve cover gasket/o-ring had failed. When it was replaced, all oil consumption ceased.

Get a new gasket from Merlin at St. Charles Isuzu -most likely the part will ship from Isuzu's warehouse in Cinci. It'll be on your doorstep in 2 days.