I think what some of ya’ll have been describing may be “piston slap” and may not have anything to do with the valves or the lifters at all. Lemme ‘splain:
In cold conditions, my car (a ‘95 Honda Civic) makes a knocking sound. I have heard stuck lifter before but this sound is very different ... it’s much deeper. The colder the air temp, the louder the sound. What is happening (supposedly) is that the pistons skirts are shorter in modern cars as the engine builders are looking to get more power through the reduction in reciprocating mass. These shorter skirts wear faster and under cold conditions, the shrunken, slightly worn aluminum pistons are allowed to rock back and forth in the cylinder making the “slapping” or “knocking” noise. Once the motor begins to warm up, say 5 minutes, the pistons expand and fit tighter in the cylinder. That’s why the noise disappears gradually over the first few minutes. Altogether different are noises which last for mere seconds which could be attributed to lifters being pumped up and restrictive oil filters.
I have heard other theories about piston slap involving the rings losing their sharp shoulders (allowing the piston to rock in the cylinder) as well as wrist pin wear. I just don’t know enough about these to describe them in much detail.
It’s the design of the engine which allows this to happen after a few years ... but some oils seem better at preventing it and others allow it to manifest sooner. Earlier versions of Mobil 1 (their tri-synthetic) had a weak, emissions-friendly anti-wear package with few metallic additives. Cars which are ...
1) Prone to piston slap (by design) and
2) Life-long users of Mobil 1
... seem especially prone to this highly annoying noise.
It’s odd, though. I used Mobil 1 almost exclusively up until 100,000 miles and my car never burned a drop of oil ... even while it knocked so loudly bystanders were sure it was about to throw a rod.
Stuck lifters I have heard make a distinct clicking sound upon start up after the engine has been sitting for a while ... even in warm weather. And, as the lifter unsticks itself, the noise goes away suddenly. A stead “tick, tick, tick ...” and then relative silence. Just normal engine noises like the whine of accessory belts. The two phenomena can’t be mistaken for each other, they are too distinct.
The only thing I have found which really makes a difference (for sure) in quieting down piston slap (once it has manifested itself) is Red Line oil ... even their 5W30.
Right now, I am using Schaeffer Supreme 7000 synthetic blend and will be sending away a sample in another week or so to be tested. This car is currently making a new ticking/knocking noise so I can’t say for sure whether the Supreme 7000 is as effective as the Red Line or not. It’s just not a fair/even comparison.
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Bror Jace