hydraulic lifters tapping at highway speed

Iíve got a 95 5.7 L Chevy Box truck (FI), only about 50k miles
Runs great all day on local roads, but as soon as itís on the highway
(over 55 mph) for a few minutes, the lifters atart to rattle.
There is no drop in oil pressure, and the oil Iíve changed the oil every 1,000 miles three times.
Once itís off the highway, a few miles later itís back to normal.
There is no drop in performance, so it must be a lifter that collapses when it gets hot?
Any ideas/suggestions?
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your HEARING SPARK KNOCK !!
Tor wrote:

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Spark knock .. a 10 year old truck with only 50k is probably all Carboned up!
Tor wrote:

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Get a can of "top engine cleaner" from your local GM dealer Part # 1050002. I havent tried it yet, but I am going to run a can thru my Seville STS with 165K
Like 6 or 7 dollars and suppose to remove all the carbon and other crap from the top end of your motor.
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something wonderfully witty:

All it did was make mine worse. Instead of tapping, they started sticking.
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get a spray bottle with some water and mist it in the intake. better than most snake oil. The steam with break down the carbon. Only real proper way to clean it is pull the heads but then you find broken stuffs and you go broke.
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I went to straight 30 wt HD oil and my lifter noise went away. Good Luck....Pete in MS

http://www.autoforumz.com/Chevrolet-hydraulic-lifters-tapping-highway-speed-ftopict106173.html
http://www.autoforumz.com/eform.php?pI4766
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