Hello everyone, I'm a bit of a newb when it comes to oil and I'm here to learn from the best! I've got a 4cyl S10 with 140k miles on it. I've owned it for 3 years and bought it with 100k on the clock. I've been doing 3k mile change intervals with penz hm and a puro classic since I drove it home. I've just switched to maxlife on my last change a couple days ago because there was a bit too much startup noise with the penz and I've had a very slow leak that appears to be coming from the back of the engine block. No oil is burned between changes and the leak isn't even heavy enough to require any oil to be added over 3,000 miles. While I was changing the oil, I figured id pour a small sample into a glass jar and look at the condition and give it a smell instead of letting it all vanish into my dirty old drain pan. The color looked ok, but there was a bit of a gassy smell to it. I have a vacuum gauge installed and the reading at idle remains high(21" or so) and I've done a couple 'tests' using the gauge to get an idea of overall engine health. I think the rings are ok but I'm tempted to do a compression and/or leakdown test just to be sure. Any other ideas as to what may be causing this odor? Just to note, it's my dd and sees highway speeds/10+ mile drives daily so its always brought to operating temp each time it's driven Thanks!