"knock" at 1100rpm ?

[90Haccord]

Just noticed something funny, my car is "knocking" when its started.
As with normal hondas, when I fire it up after its set for 24 hours with no operation it goes to 1100-1500rpm's to "warm itself up". During this period it sounds as if its KNOCKING that I've never noticed before.

Once its up to temp, and idles at its normal idle of 750rpm I don't hear it.

Only thing I've done recently is run a tank of shell v-power 93 octane through her. Switch back to 89 octane?

I could be making this up, but I'm 80% certain I never heard it before. Maybe its time to go back to 10w30 motor oil. Currently its using 5w30 with 228K on her. Thicker oil maybe needed?
Say 10w30 summer time, 5w30 winter time.

[champagneaccord]

The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.

[C91BLX7]

Valves probably need to be adjusted or just are noisy

[visualpoet]

It would help if you could get us a sound file to hear. Trying to diagnose a described noise is nearly impossible. What you consider a knock, I might describe as a solid tap and someone else might call a rattle.

[deevergote]

There's no reason to run anything more than 87 octane on a stock engine. The octane rating means nothing in that case, other than the fact that you're wasting your money.


Feel your spark plug wires when it's knocking. See if you can feel the knocking in any of them. If so, you may have damaged plug threas. Just a shot in the dark.

[johnl]

Piston slap?

I can't see it likely to be octane if it didn't 'knock' before on that fuel but does now. Maybe it's to do with piston / bore wear and the thinner oil you're now using?

Could be (?) cold (and worn) pistons being smaller diamater (before they expand with heat and become 'tighter' in the bores) rocking in the bores causing the 'knocking' sound (a kind of rattling?). This would be 'piston slap'.

The thinner oil (when cold) may be providing less of a 'cushion' between the pistons and bores so the noise made by 'rocking' pistons may be more evident than with a thicker oil (i.e. an oil that is thicker at colder temps as a 10W will be compared to a 5W).

???

[Losiracer2]

can you feel the knocking also or just hear it? I'd first go out and adjust your valve clearance. Its supposed to be checked every 15K miles, could just be the tapping possibly?

[90Haccord]

I don't feel anything, its just a slight "tap" but I'm sure it wasn't there before. Will try to get a video tomorrow, hell it could just be in my head. Although I'm pretty sure its a new sound.

Spark plug wires are brand new(NGK blue's)
Spark plugs are brand new (NGK v-power $1.59 at autozone)


I have no idea how to do a valve adjustment, what does it generally cost?

[Lroy onDA scene]

i think ur motor is going bad...mine would do that when i would turn it on and it would go away...next thing i know..its got worse and my motor messed up..i ran it without oil..id never refill it cuz it would leak oil alot

[johnl]

i ran it without oil..id never refill it cuz it would leak oil alot

I suppose that's one way to reduce an oil leak....

[deevergote]

Motors don't often "go bad" unless you do something stupid like let them run dry... Things fail, but drastic failure is usually due to negligence.



If it's a slight sound, it may just be valve tap. Have the valves adjusted, or learn how to do it yourself, and see if that fixes things. It may just be a normal noise that you've never noticed before. These engines are notorious for valve and injector chatter. Some is normal with age, some is just a sign of a necessary adjustment.

Piston slap is also a possibility, but that would require some pretty major wear to ve evident... though thin or low oil would increase that possibility, I would think.

However, changing from 10w30 to 5w30 shouldn't matter at this time of year. The first numer, the "w" weight... is the winter weight. That's the viscosity rating when the oil is cold. When the oil is warm, at about 100 degrees F, you're looking at 30 for both. It doesn't take an engine more than a couple minutes, maybe even less, to get up to normal operating temperature in the summer. That should have little or no bearing on your engine's operation.