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New noise after oil change


jdarwin
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I've searched around the forum but did not find an answer so I'm putting this out there: 1976 purchased in May this year. Changed the oil recently and there is a knocking sound that now occurs at idle. Was not apparent before I changed the oil. It does not begin until after 10-15 seconds of running. It then slowly goes away as the engine heats up. I used 20w50 Valvoline as recommended on this site. Also, a Mann oil filter from Autohausaz. I re-adjusted the valves last night and that did quiet some of the valve chatter but the knocking noise is still there, albiet maybe not as pronounced - again, until the engine is warm and then it is only very slight. I've read were the Bosch has an anti-drain feature. Could the lack of this feature cause this? It has a Bosch filter on it before the change. I'm not certain of the oil brand / weight that was in the car previously. I've e-mailed the PO to determine. Thoughts?

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From your description sounds like piston slap. As the pistons warm they expand and the noise diminishes or disappears completely. Is the noise as apparant on restart after the engins is warm?

No. If I shut down for less than 30 minutes, no noise upon startup. If indeed piston slap as you describe, it is odd that it did not do this prior to the oil change (or is it?)

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Guest Anonymous

My '76 makes that noise on startup occaisionally. I go through the vacuum lines at the dist. for leaks and correct hookup. I think the noise comes from excess timing advance until the retard vacuum gets at the proper level. Look for a leak in the retard line.

This is if you still have a vacuum advance on your dizzy.

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If you're using a heavier weight oil than you were before, it could simply be the lack of lubrication on startup. I can't say this enough- NO oil protects an engine sufficiently at startup. The thicker the base stock, the longer it takes to thin to a protective state.

I don't understand the point of a 20W-50 synthetic oil. It's a 50W base stock with thickness modifiers to make it act like a 20W at startup. If you're going to use a 50W oil, why not go to a 0W-50 or 5W-50 that will at least give your engine a shorter warmup interval to thin the oil to a lubrication state?

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If you're using a heavier weight oil than you were before, it could simply be the lack of lubrication on startup. I can't say this enough- NO oil protects an engine sufficiently at startup. The thicker the base stock, the longer it takes to thin to a protective state.

I don't understand the point of a 20W-50 synthetic oil. It's a 50W base stock with thickness modifiers to make it act like a 20W at startup. If you're going to use a 50W oil, why not go to a 0W-50 or 5W-50 that will at least give your engine a shorter warmup interval to thin the oil to a lubrication state?

Don't say NO oil protects at startup. Some oils have polarizing agents in them to cause oil films to hold to magnetic material like steel. (Don't get carried away with holding metal products. If there are metal products in the oil, there are other major problems). I had (and may still have) documentation from GM dated 1979 referring to this feature. There is also a site that sells a proprietary engine cleaner that disscusses this issue with regards their cleaning process.

Also don't categorize all oils multigrade oils as having viscosity improvers (termed above as thickness modifiers above). This is true with dino oils, but some synthetic brands will be in spec as a multigrade w/o VI improvers. However, those 5W-50s and 0W-50s won't be a natural multigrade. A 20W-50 or 15W-40 is about as much as you can squeek out w/o a VI improver.

Back on the original post question: It most likely is not the drainback feature of the filter. That rubber flapper you see in the holes (inlet holes) around the stud (clean oil outlet) is the anti-drainback feature.

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Don't say NO oil protects at startup. Some oils have polarizing agents in them to cause oil films to hold to magnetic material like steel. (Don't get carried away with holding metal products. If there are metal products in the oil, there are other major problems). I had (and may still have) documentation from GM dated 1979 referring to this feature. There is also a site that sells a proprietary engine cleaner that disscusses this issue with regards their cleaning process.

Also don't categorize all oils multigrade oils as having viscosity improvers (termed above as thickness modifiers above). This is true with dino oils, but some synthetic brands will be in spec as a multigrade w/o VI improvers. However, those 5W-50s and 0W-50s won't be a natural multigrade. A 20W-50 or 15W-40 is about as much as you can squeek out w/o a VI improver.

Back on the original post question: It most likely is not the drainback feature of the filter. That rubber flapper you see in the holes (inlet holes) around the stud (clean oil outlet) is the anti-drainback feature.

Key word: "Sufficiently." You still have a film, but flow is the key characteristic for continuous lubrication.

More later- too much to say at work.

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Actually after 36 years of ownership and driving the same car as a DD nothing surprises me with regards to maintenance anymore. I have made repairs on a certain area only to have something go wrong coincidentally on startup after the repair. If rod bearings are the issue, you might have oil pressures issues as well. But it still sounds like piston slap. Just a thought.

Earl

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It actually could be the anti drain back valve. It does help keep oil from draining in both directions (but acts as a check valve with pressure). If too much oil drains back to the pan, the engine will take a bit of time to make enough pressure, mine does make noise for a few seconds after an oil change even with cranking for pressure before letting it start, but with the anti drain back, it doesn't make noise until the next oil change.

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One more piece of info; although the noise appears after 10-15 seconds after starting, it will go away or dramatically diminish if throttle is added - say, 1500-2000 rpms. It reappears once back to idle and slowly goes away as the engine reaches operating temp. After driving for 15-20 minutes, there is no evidence of noise. Upon startup, it seems to be coming from the top/front of the engine.

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