So I lost my haynes manual and need to know how much an 86 2.3 isuzu trooper takens in engine oil?

The 2.6 is 4.5 quarts; so the 2.3 should be the same or right around that. If noone steps in with an exact answer, just start with 4 quarts and then fill a little at a time until the dipstick reads full.

Thanks strawmyers it was 4.4qts. So I went 3qts or royal purple 10-30 and 1qts of slick50 engine treatment, I really didnt need the treatment due to the fact I have a new motor but I fugured it would keep the internals cleaner longer.

Actually if you want to possibly ruin your motor you'll use Slick 50. Dupont, the originator of the Teflon additive that's in Slick 50, doesn't even recommended it for that useage. Of course they can't control what companies due with the additive once it's sold.

The teflon additive builds up on piston lands and gets caught on sharp edges in oil passages and your new motor won't benefit from that!

You'd probably be better served by using a quality synthetic oil. I've been using Rotella 5W-40 synthetic in my rigs and they run very well.

Here's some info on PTFE as an oil additive:

http://skepdic.com/slick50.html

Cheers..........ed