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Knock on Start Up?

T

Tony_SS

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Location
Washington, MO
When I first start up I hear a couple knocks, for only a couple seconds, then it goes away. If the engine is warm (lubed) it doesnt' do it when I restart. Do I have a stuck lifter that knocks until its oil? Or what else could it be? TIA.
 
what year is the motor? how many miles? when's the last time you changed the oil?

My burb used to do that, it had 260k on it, the knock wasn't as bad right after an oil change, and then i was living in Phoenix, so in summertime i wouold run 20/50 wt oil, which also seemed to help alittle.

lifters will be a high sounding tick, this knock is either a piston slap, or more likely bottom end noise. I never worried about it since it was a high mileage motor, i just kept the oil changed/clean.
 
1990 350, factory engine 168,xxx miles. I just changed the oil but didn't know the last time it was changed before that.

Should I still use the 5w30 oil?
 
in your climate i wouldn't go any thicker than 10/40, the 5/30 will get to the bearings and get everything oiled up alot faster though. I was just never a big fan of running a thin oil in a high mileage motor, pluas as mentioned, i daily drove the Burb in Phoenix HOT summers alot, so the 20/50 did it's job as far as i am concerned.

I heard from somewhere once, that in extreme heat, the oil will actually break down a full grade during continous driving, like i used to do out there.

I just had a brand new motor installed in the burb 2 months ago, just now switched to a full synthetic oil, just the little bit i have had it, i will continue to keep running it. May be an option for you to consider.
 
Likely piston slap or rod bearings. If you have the funds, a tear-down and refresh might be in order. A rebuild is generally cheaper before you throw a rod ;)
 
Mines been knockin on start up for the last 100k miles....it has 268k on it. As soon as its warm, it goes away. Im just waiting for it to stop workin, so I can put in my new motor thats been sitting and waiting.
 
Chaddy said:
Mines been knockin on start up for the last 100k miles....it has 268k on it. As soon as its warm, it goes away. Im just waiting for it to stop workin, so I can put in my new motor thats been sitting and waiting.
Click to expand...

Thats what I like to hear! What kind/brand of oil are you running?
 
valvoline 10w30. When it was my DD, I would change it every 2500 miles. Now I just do it every spring.
 
Chaddy said:
Mines been knockin on start up for the last 100k miles....it has 268k on it. As soon as its warm, it goes away. Im just waiting for it to stop workin, so I can put in my new motor thats been sitting and waiting.
Click to expand...


Same here. My Suburban knocks on start up every morning. But as soon as the oil pressure comes up, it goes away. I bought Fillmore last year and the odometer read 25,000, but I'm not sure if it's 125,000 or 225,000. And I use Valvoline 10W40.

I'm not too concerned about it because every Chevy I've owned has done this.
 
I had a friend with a 94 chevy truck with a 350, his knocked on startup for proabably about 100k too. It must have been main bearings cause rod bearings wouldn't have lasted that long, or could have been a worn thrust bearing. Make sure you are using a good quality oil filter with the drain back valve.
 
It's probably a main bearing. As long as the knock goes away after 3 seconds or so I wouldn't worry about it. My 2000 silverado has had the knock for over 100,000 miles and counting.
 
I've had a few GM engines that sound like a woodpecker for a few seconds on a cold start,and I never lost much sleep over it if it went away quickly..its just a bearing on the loose side getting pressurized with oil after it starts,which quiets it..

I have found a nearly clogged oil pump screen on a few engines I had that did this,and after I replaced the screen and pump it stopped doing it..(had the oil pan off to replace the timing chain on one engine,the other one the pan rotted thru)..
I find the #1 main bearing on many Chevy V8's gets the most wear,due to the strain of the v-belts and A/C pump,plus it being the farthest one from the oil pump and starves the longest before oil gets to it..its probably the one that raps and then gets quiet!..excess end play can do the same too..
 
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