I had planned on keeping my Tahoe "forever", so I really babied it. Mobil-1 oil every 4,500-5,000 miles (oil monitor usually still 40%), coolant flush and transmission fluid change every 3/36, etc. The engine starting drinking antifreeze just about the time it crossed 100,000 miles. I was adding well over a quart per month. My local shop did a leak-down test but couldn't find any problems. They replaced the overflow bottle cap and told me to monitor the antifreeze level.

I did some Internet research and discovered these engines are prone to head cracking (GM TSB says "porosity" develops). My heads were the dreaded 706 Castech heads, so I started looking for symptoms. Sure enough, there was a puff of white smoke when I started the truck. I hadn't noticed anything unusual when I changed the oil, but I looked under the oil fill cap and found the dreaded foam. I had always heard you shouldn't put new heads on an older engine and both my trusted mechanic friends agreed. I ended up putting a Jasper engine in the truck with a new water pump, engine mounts, and other consumables. A mere $4,000 later, my truck was good as new for at least a few months. This was the only engine failure I have ever had on a vehicle in 30+ years of driving and, ironically, it was on the vehicle that I maintained the most fanatically.