Knock Sensor problem and DEX-COOL!

[roaddirt]

In some of GM forums I saw several threads describing Knock Sensor problem caused by DEX-COOL coolant.
Normally internal portions of Knock Sensors are seated in “water pockets” in engine.
After removing sensors, owners found “water packets” dry due to coolant sludge plugging holes from which coolant comes to pockets. This will cause improper Knock Sensor signal and cause spark timing problems, mostly spark timing retards when you do not need it.
Does anybody know more about this issue?

[bignoisey]

Since the subject of Dex-Cool was brought up..... The label under the hood and the owner's manual say the stuff is OK for five (yes 5) years. I was a little suspicious that that might be a bit long and the sludge described in the other guy's cooling system seems to confirm that. Does anyone think we should change it out earlier than 5 years? Does anyone besides me even own a car that long any more? I have a 2000 Century with a intake manifold coolant leak, so mine probably won't even make it for 5 (if I ever get around to fixing the leak).

[pcv]

Depends on where you live and driving conditions, I'd recommend every three years, flush the cooling system. Otherwise, everytime the coolant appears sludgy, flush it and replace with new dexcool.

[roaddirt]

Originally Posted by bignoisey

Since the subject of Dex-Cool was brought up..... The label under the hood and the owner's manual say the stuff is OK for five (yes 5) years. I was a little suspicious that that might be a bit long and the sludge described in the other guy's cooling system seems to confirm that. Does anyone think we should change it out earlier than 5 years? Does anyone besides me even own a car that long any more? I have a 2000 Century with a intake manifold coolant leak, so mine probably won't even make it for 5 (if I ever get around to fixing the leak).

My 1999 Century with 40K has lower intake manifold oil leak as well. It seems to be common problem with all 3100 engines for years and GM does nothing to fix the flow. Does anybody have an idea how much they charge to replace lower intake manifold gaskets?

[bignoisey]

I was quoted a little over $400, for my 2000 Century 3.1 but the service guy apologetically said "But the gaskets are pretty expensive ya know". I'm going to do my own when I get the time. You'd think GM could build engines right by now, huh? Does anyone have suggestions for preventing intake manifold coolant leaks from recurring once we do all this work? I'm not going to do this every 40-50K miles.