Is the famous Fram "knock" at startup caused by the ADBV or low flow?

[Big O Dave]

With the Fram Extra Guard (PH series) of filters, I've personally experienced lifter noise at startup, and of course, I've read that it is a near-universal experience among those who've used Fram Extra Guards here at BITOG and also at other sites.

This is normally attributed to the ADBV, but after seeing the flow rates for these filters on the "Grease" filter study, I'm starting to wonder if this startup noise is really caused by low flow, rather than ADBV problems.

Thoughts?

 

[kanling]

If it is cold I think low-flow can cause startup noise...since the cold oil would be thicker and more resistant to flow through the media until it warms up a little.

 

[Ugly3]

quote:

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Originally posted by kanling:
If it is cold I think low-flow can cause startup noise...since the cold oil would be thicker and more resistant to flow through the media until it warms up a little.

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Would not the bypass valve have to fail in order for this to happen?

 

[ToyotaNSaturn]

I'd be willing to bet it's the ADBV. No oil to lubricate the top end at startup.

 

[T-Keith]

There is more to it that just the ADBV letting the oil drain, although that is a big problem. I've seen cars with an AC filter run silently, then switching to a Fram the noise comes and continues even minutes after startup. Since in grease's test the AC didn't greatly outflow the Fram I don't think that entirely it either.

It a certainty that the Fram ADBV allows oil to leak between the valve and the endcap and also pushes in to allow full bypass.

-T

 

[kanling]

quote:

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Would not the bypass valve have to fail in order for this to happen?

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I notice that the bypass pressures on "compatible" filters can be quite a bit different.

Wix 51348 bypass pressure is 8-11 PSI
while the Purolator cross #L10241 is 12-15 PSI for example.

It might be the case that the cold flow is lower than needed but that the pressure just isn't quite enough to open the BPV fully sometimes?

 

[Ugly3]

Oil pumps are "positive displacement pumps", the flow of oil at a given RPM is always the same, the only thing that changes is the pressure resulting from restriction.

 

[Schmoe]

What kind of engine is it? Like the Ford modular engines, most will make a little noise until the oil reaches the top on a overhead cam type of engine.

 

[kanling]

quote:

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Oil pumps are "positive displacement pumps", the flow of oil at a given RPM is always the same, the only thing that changes is the pressure resulting from restriction.

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Good point, Ugly3. There is a maximum pressure that the oil pump will produce before it limits out on pressure relief, though. I have no idea what that pressure would be, but is it possible that it might happen with a very restrictive filter with a very high bypass pressure?

 

[Ugly3]

Not real likely, most oil pumps go into releif in the 40 to 60 PSI range, the bypass on filters are generally below 20 PSID.