I have a 01 blazer with the 4.3 vortec on it. It has 145K miles.

I have noticed that about every 1000 miles my oil level goes from the "max at operating temperature" lower down to the tip of the oil dip. The engine IS leaking from the timing cover and other places but I am not sure if it is at that level. The car doesn't leave a single drop of oil on the garage parking, it's just that the underneath is all oily. I was wondering if it could be burning small amounts of oil that the cat converter would take care of because the exhaust is clean. Any ideas?

Also, if it is burning oil, how can I figure out of its due to the valve covers or the cylinder walls are gone?

 

I am willing to bet that your oil cooler lines are leaking, they always leak.