I have a 1997 GMC Yukon w/5.7l engine, SLE package w/160,000 trouble free
miles.
During a trip to meet friends in Canada, my wife was driving and noticed the
temp
guage was pegged (260 degrees). She woke me up and we limped the truck a
half mile
off the QEW to a Tim Hortons where I opened the hood and saw steam, not
water,
blowing out of a crack in the plastic radiator tank next to the upper oil
cooler fitting.
The engine was HOT. It was pinging and rattling when we shut it down.
We went inside the coffee shop to eat lunch and let the truck cool down.
When the truck was cool we filled it back up with plain water and started
the engine
and noticed  a limp as if it was missing on one cylinder. We drove the 20
clicks
to our destination  carefully watching the temp guage.When it came time to
drive home,
about 250 miles, I added a bottle of barr's leak and made it home stopping
to add water as needed.
A new dual core radiator solved the overheating problem, but I have been
pulling my hair out trying to get the
truck to idle like it used to b4 the overheating.
The scanner says intermittent miss cyl 4., and I dropped fron 18-19 mpg to
16-17mpg.
New plugs, cap, rotor, & wires didn't help.
Compression ck shows good and even across all cylinders.
At hi idle the engine smooths out and runs better.
At cold start it seems to idle better than when it'swarmed up.
It doesn't seem to be an ignition problem, could the heat have damaged the
fuel spider some how? I read in this group that when the spider leaks it
dumps raw
fuel into the intake above #4 cylinder.
I have always used Mobil 1 in this engine and the oil looked good after the
overheating episode.
Comments? Ideas?
thanks
 JR