Truck: 1997 4x4 K1500 heavy chassis with 5.7L Vortec V8, 75000 miles
I bought this truck new and for years told everyone how they should've
bought a Chevy ...perfect all the time. In the last year however, I've had
to replace the alternator, serpentine belt, idler pulley, intake manifold
gasket, fix the hose fitting (crusty) on top of the manifold, egr valve,
replace front discs, calipers and pads etc. Whew!
Then, since the idle was ever-so-very-slightly rougher than when new, I ran
a bottle of Lucas brand fuel injector cleaner through it (full tank). About
1/4 of the way into the tank following that, I started getting very loud
lifter knock (scary loud) on the passenger side of the motor. Oil level was
fine and looked OK. Always have used Mobil 1 Synthetic, 5-30W as spec'd,
changed at 3k mile intervals. This oil was about 500 miles from a change.
The lifter noise would quiet down after running for awhile, or driving very
slowly with a very light pedal. Note that the coolant level was low and I
had not filled it since I was out of Dexcool, but the temp gauge said the
usual 185 F or so just like always.
Over the next week, it got worse to the point where you could hear loud
noise from the entire valve train under the valve covers on both sides of
the motor. So far, my mechanic (non-dealer) and the dealer had no clue and
neither did I. I was so busy listening to the noise (and worrying to death
about thousands of dollars in taking motors apart becoming necessary etc)
that I never did think to check oil pressure so I have no data on that, even
On a whim, I changed the oil with my usual Mobil 1 and put a new filter like
always (Purolator Pure One), filled the reservoir with Dexcool. The motor
still knocked and made noise. When shutting down, a bunch of the coolant
chugged into the motor so I refilled it. Again, a bunch of it went into the
motor. Topped off with water and it's been stable and quiet (no gurgling
The next morning, the motor started up and sounded brand new ...absolutely
no noise. Even the very light tick-tick-tick from the lifter that had
always made that noise right from the factory had gone away and the motor
even runs smoother than ever, even at idle. Like magic....
It's been fine since then and it's been about a week now. Once, it did
knock a little upon start-up and I noticed the oil pressure was at 20psi on
the gauge and the knock immediately quit as the pressure came up. My normal
oil pressure is one mark above the 40 psi when cold, and right at 40 psi
when driving. Now, the oil pressure is averaging one click above the 40 psi
mark when driving, and can be as high as 50-60 psi on start up ...higher
than it used to be, even with new oil.
My mechanic now guesses that I had a sticky oil pressure relief valve that
was recently sticking open. He recommends flushing out the motor (oil) to
clean out deposits and what not.
Sorry for the loong story, but I'm puzzled ...does the above sequence of
events make sense to anyone? Comments on what is or was wrong? Does it
make sense to flush out the oil to clean things out? Why did new oil and
topping off the coolant fix it???
Thanks a mil!