Oil light on when car reaches operating temp then engine knocks

Your hearing lifter noise common in most cars in cold weather I have a 2001 sc1 same engine as yours here's how to get rid of that ticking sound go buy a quart of Lucas synthetic motor treatment change your oil and leave it 1 quart low add the Lucas synthetic oil stabilizer within 1 week you will not hear the noise agian reason your hearing the noise is there's no oil at the top of the engine on a cold start oil when cold is thicker hints why your noise in your engine what Lucas does is eliminate the dry start by the way my engine has 288,000 and does not use a drop of oil after you use this product you should use it every oil change you will see your car will thank you regards Chris

put an engine flush in first . run the engine on tick over .till oil is hot then drain it. do an oil and filter change may have a build up of carbon in the engine .the flush should deal with that .use 20/40 oil .

hello there
I looks like your oxygen sensor,Try to disconnect and then see what the car does?Let me know.You may need to adjust the fuel mixure,seem it is running a little rich that is why the car in idle goes up and down.
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Often a sticky lifter. Try an oil change with a premium oil of the right viscosity, and an additive designed for the problem.

the one thing in your statment is the knockes/knocking this what is known as the big ends and indicates the engine is under pressure and needs a lot of repair.If when you start the engine when cold if you stand at the back of the car and if the smoke coming out of the exhaust has a blue tint/ie like a old ladys hair tint ,as im sure you will see.[bottom line] the engine needs replaced.adrian,,,,

If this is a loud knock from lower part of the engine then its the crank bearings, I personally think that the engine is done.

this engine has forged pistons whitch expand more than hyper-u-tec-tic pistons when heated . this is normal for this engine . my brother has a chevy silverado 2001 1500 4.8Lwith 650,000 kms and he said his made that noise when it was brand new and the dealer said this is normal. the truck still runs like new with lots of power and it still makes that noise before it reaches operating temp then goes away.My brother uses lucas oil treatment and it helps quiet the knock a little when cold.

Does the oil light come on or the knock occur during the engine warm up after a cold start?
There could be a couple of problems causing the issue. You could have an oil pressure pump or pump pressure regulator sticking. I would have a mechanical oil pressure gauge installed and verify oil pressure at idle and 2500 rpms to make sure oil pressure is in normal ranges.
You could also have excessive piston rod bearing, crankshaft bearing or cam shaft bearing wear that will cause oil pressure to drop too low to prevent the rod knock your hearing at 2500 rpm.
You said a knock and not a ticking noise,so I don't believe a lifter is the issue at 2500 rpm.
Start with the oil pressure check and go from there.
Let me know.
Regards,

try running a higher viscosity oil.
Instead of 5w30 (W stands for winter or cold viscosity) try a 10W30 or maybe more like a 20W50 the higher number is when the oil heats up.
You may try and add a can of No-Smoke or STP oil additive since you recently changed oil.

Is there any smoke when you first start it? what is happening is the valve seals are probably worn and letting the oil seep past them. when your engine is first started it has no oil or very little oil at the top of the engine, thus causing the knocking noise. could be more but this is a most likely answer. oh and is you haven't changed your oil every 3,000 miles you had beeter start doing it.... answer knocking sounds usually come from bottom of engine try a better quality and correct viscosity oil