2000 Astro Oil Pump Ticking On Start Up

[CHEVY1]

Hello

Just Recently The Following Has Accured. It Does Not Happen Every Time When Starting. There Is A Ticking Noise From The Back And Below The Engine After Start Up. It Some Times Last Seconds And Others 1-2 Minutes. I Have Been Told It Is The Oil Pump And Screen Which Is Loctaed In The Oil Pan. Which In Order To Be Removed Must Take Doen Exhaust And Then Oil Pan Replace And Put Back Together.

I Have Been Told That This Problem Is Not Urgent Now , But If Does It All The Time Or For Longer Intervals Of 2 Or More Minutes It Is Time To Get Er Done.

Any Help On This Subject Would Be Greatly Appreciated

Thanks

[old_master]

The symptom that you're describing sounds like piston slap. This is very common on the 4.3 engine. The knock is only noticeable very briefly when the engine is cold. As the wear increases, the noise lasts longer. Piston slap occurs when the piston is at bottom dead center, (BDC) and starts to go up. The lower part of the cylinder wears and the piston wobbles trying to center itself in the cylinder. As it wobbles, the skirt of the piston slaps the lower cylinder wall causing an audible knocking sound. Piston slap is caused by insufficient oiling of the lower cylinder wall. It is most noticeable on a cold start due to the oil running off of the cylinder wall while the engine was not operated. After startup, oil is splashed on the lower wall and the noise stops. Depending on how severe the wear is, the pistons and rings must be replaced and the cylinder bores machined.

[CHEVY1]

I Appreciate The Info. I Had A Bunch Of Us Guys Standing Around It Yesterday. Monday Morning Was 20 Plus Degrees In The Morning. Van Started With No Noise. I Drove It 39 Miles Sat For 8 Hrs At Work. I Then Go Out To Start It And Tick Tick Tick Would Not Stop. I Got A Ride Home. Turned Ths Key This Mornig @ 40 Degrees No Noise. I Don't See How This Is Consistent Enough To Be Such A Big Problem? I Don't Really Know Much About Motors All Though I Heard The 4.3 Was A Runner.

No Way It Could Be An Oil Pump Like You Said And So Did The Guys.

I Have Now Been Told Pistons, Rod Or Lifter, Oil Pump....ahhhh
I Don't Know What To Do Or Where To Take It. I Have About 3 Weeks To Get It Done...

Thanks Again

[old_master]

Piston slap is noticeable immediately after start up, each time the engine sits 8 hours or more with ambient temperature below approximately 40F. The "slap" occurs for about 20 seconds, longer with lower temperatures. It is noticeable when the engine idles, and increases in intensity when RPM is increased. The noise usually is not noticeable while RPM is decreasing with closed throttle, (after revving). The sound is very different from a valve lifter "tick", and unlike the deeper knock caused by a worn rod or main bearing. Without engine disassembly, it is difficult even for an experienced and trained technician to differentiate piston slap from a worn wrist pin. The sounds and characteristics are virtually identical with one exception: a worn wrist pin will typically make noise even after the engine is warm.

General Motors recommends 5w30 motor oil in the 4.3 engine. If you are using 10w30, 10w40, or thicker oil, that may be a contributing factor making the noise more noticeable. The thicker oil takes longer to circulate and lubricate the lower cylinder walls.

[Blue Bowtie]

Originally Posted by old_master

Piston slap is noticeable immediately after start up, each time the engine sits 8 hours or more with ambient temperature below approximately 40F. The "slap" occurs for about 20 seconds, longer with lower temperatures. It is noticeable when the engine idles, and increases in intensity when RPM is increased. The noise usually is not noticeable while RPM is decreasing with closed throttle, (after revving). The sound is very different from a valve lifter "tick", and unlike the deeper knock caused by a worn rod or main bearing. Without engine disassembly, it is difficult even for an experienced and trained technician to differentiate piston slap from a worn wrist pin. The sounds and characteristics are virtually identical with one exception: a worn wrist pin will typically make noise even after the engine is warm.

Further, a wrist pin can sometimes be diagnosed separate from skirt slap by disabling the ignition on a suspect cylinder, or relieveing compression on that cylinder and running the engine. An astute technician can even use a stehoscope/probe through the spark plug hole on a fully warmed engine and differentiate skirt slap from pin boss wear. Although, performing that on an Astro would not be an easy task, and if you are fortunate enough to have an AWD version, if would be far easier to remove the oil pan with the engine in the vehicle (it's WIDE open) and diagnose the problem.



With the pan removed, checking skirt clearance with a feeler is cake. The W engien is not as prone to skirt slap in later versions as the early balance shaft models. It seems that 1995-97 were the more prone years, but it certainly can still occur.

General Motors recommends 5w30 motor oil in the 4.3 engine. If you are using 10w30, 10w40, or thicker oil, that may be a contributing factor making the noise more noticeable. The thicker oil takes longer to circulate and lubricate the lower cylinder walls.

Above 0°F (-18°C) the accepted lubricant is 10W30, according to the 2000 Astro Owner's Manual (Pub. 20STFF01). 5W30 is recommended below 0°F, and accepted above that temperature. Even though the filler cap reads "5W30" and it is accepted at all temperatures, I avoid it entirely. If I used mineral oil, I might xconsider it. Since I want my hardware to last until I'm ready for a change, I don't use mineral oil. PAO 10W30 (which is really misleading, since the antiquated SAE viscosity ratings don't apply well to synthetics) pumps, flows, and lubricates better than 5W30 or even 0W30 mineral oil in cold temperatures.

Be careful about "blanket" or "universal" statements.

I agree with the Master - an oil pump/pump shaft is a very remote possibility. That would also more likely be making noise at warmer temperatures instead of cold, and would also be serviced through the oil pan removal.

Another obscure possibility is loose flexplate bolts, but that again is less likely to be temperature dependent.

Whatever the cause, it is very unlikely that it will just go away by itself, and without problems. The longer you wait, the greater the risk of severe damage or failure.